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PATH: Diagnostics > Diagnostic Routines > Powertrain > Engine Controls - 5.0L
and 5.7L > DTC P0420 Catalyst System Low Efficiency Bank 1 (Over 8600 GVW
(C6P))
DTC P0420 Catalyst System Low Efficiency Bank 1 (Over 8600 GVW (C6P))
NOTE
Applicable vehicles:
 Chevy Pickup, GMC Pickup, Suburban, Tahoe, Yukon (VIN C/K)
DTC P0420 Catalyst System Low Efficiency Bank 1 (Over 8600 GVW
(C6P))
Click to Enlarge
Circuit Description
This diagnostic test is designed in order to measure the efficiency of the threeway catalytic converter (TWC) system. Catalytic convertor efficiency is a
measure of its ability to store oxygen after converting the levels of
hydrocarbon (HC), carbon monoxide (CO), and oxides of nitrogen (NOx) to
less harmful gases. The control module is able to evaluate the catalyst
efficiency once the vehicle has met the enable criteria and the vehicle is at idle
instead of the steady cruise speeds used in the past.
Once the conditions for running this diagnostic trouble code (DTC) are met,
the control module commands either a lean or rich air/fuel ratio depending on
the current state of the exhaust oxygen level. The control module issues a rich
command if the exhaust is currently lean, or a lean command if the exhaust is
currently rich. After completion of the first command, a second and opposite
command is issued.
For example, if the control module were to command a rich mixture, the
upstream heated oxygen sensor (HO2S) voltage would increase immediately.
The rich mixture is delayed in reaching the downstream HO2S due to the
conversion process occurring within the converter. The higher the efficiency,
the more the delay before the rich or lean mixture is detected by the
downstream oxygen (O2) sensor. As a result of the lower conversion efficiency
within a damaged or poisoned catalyst, the delay in the rich or lean mixture
reaching the downstream O2 sensor is significantly shorter. This DTC
monitors the amount of time required for both the upstream and downstream
HO2S voltages to cross a calibrated voltage threshold in response to the rich or
lean command.
Conditions for Running the DTC
 No active secondary AIR DTCs
 No active CMP sensor DTCs
 No active ECT sensor DTCs
 No active EGR DTCs
 No active fuel trim DTCs
 No active IAC DTCs
 No active IAT sensor DTCs
 No active MAF sensor DTCs
 No active MAP sensor DTCs
 No active O2 sensor DTCs
 No active transmission DTCs
 No active EVAP system DTCs
 No active TP sensor DTCs
 No active VS sensor DTCs
 No active misfire DTCs
 The engine speed is 1,000 RPM or more for more than 40
seconds since last idle period
 The engine has been running for at least 360 seconds and the
long term fuel trim is stable
 The predicted catalyst temperature is at least 390°C (734°F)
 The system is in closed loop
 The BARO is 73 kPa or more
 The IAT is between -7-117°C (20°-167° F)
 The ECT is between 75-117°C (167-243° F)

The engine has been idling for less than 120 seconds
 The actual engine speed is within 100 RPM of the desired idle
speed
Conditions for Setting the DTC
The VCM determines that the oxygen storage capacity of the catalyst has
degraded below a calibrated threshold
Action Taken When the DTC Sets
 The control module illuminates the malfunction indicator
lamp (MIL) the first time the diagnostic runs and fails.
 The control module will set the DTC and records the
operating conditions at the time the diagnostic fails. The
control module stores the failure information in the scan tools
Freeze Frame/Failure Records.
Conditions for Clearing the MIL or DTC
 The control module turns OFF the MIL after 3 consecutive
drive trips when the test has run and passed.
 A history DTC will clear if no fault conditions have been
detected for 40 warm-up cycles. A warm-up cycle occurs
when the coolant temperature has risen 22°C (40°F) from the
startup coolant temperature and the engine coolant reaches a
temperature that is more than 70°C (158°F) during the same
ignition cycle.
 Use a scan tool in order to clear the DTCs.
Diagnostic Aids
The use of fuel with a high sulfur or lead content can degrade a marginal
converter's performance. Be sure to check fuel quality.
An intermittent may be caused by any of the following conditions:
 A poor connection
 Rubbed through wire insulation
 A broken wire inside the insulation
Thoroughly check any circuitry that is suspected of causing the intermittent
complaint. Refer to Intermittents and Poor Connections Diagnosis in Wiring
Systems.
If a repair is necessary, refer to Wiring Repairs or Connector Repairs in Wiring
Systems.
Test Description
The numbers below refer to the step numbers in the diagnostic table.
3. This table checks for conditions that can cause the three-way
catalytic converter efficiency to appear degraded. Inspect and
repair exhaust system as necessary. Refer to Exhaust System
Inspection in Engine Exhaust.
6. Before the three-way catalytic converter is replaced, make sure
that the following conditions are not present:



Step
Misfire
High engine oil consumption or coolant consumption
Retarded spark timing or weak spark
Action
Value(s)
Yes
No
Go to
Step 2
Go to
Powertrain
On Board
Diagnostic
(OBD)
System
Check
WARNING
1
Important: Before clearing the
DTCs, use the scan tool Capture
Info to save the Freeze Frame and
Failure Records for reference. The
control module's data is deleted
once the Clear Info function is used.
--
Did you perform the Powertrain OnBoard Diagnostic (OBD) System
Check?
Are any other DTCs set?
2
3
4
--
1. Check the exhaust system
for the following
conditions:
 Leaks
 Loose or missing
hardware
2. Repair as necessary.
Refer to Exhaust System
Inspection in Engine
Exhaust.
Did you find a problem?
--
1. Verify that the correct
original equipment threeway catalytic converter is
installed.
2. Check the converter for
the following:
 Dents
 Severe
discoloration
--
Go to the
applicable
DTC
Go to Step
table
3
Go to
Step 5
Go to Step
4
Go to
Step 5
Go to Step
6
Step
5
Action
 Holes
3. Ensure that the oxygen
sensors are properly
installed and that the
wiring connections are
properly retained and not
damaged.
4. Repair as necessary.
Refer to Exhaust System
Inspection in Engine
Exhaust.
Did you find a problem?
1. Using the scan tool, clear
the DTCs.
2. Start the engine.
3. Allow the engine to idle
until the engine reaches
normal operating
temperature.
4. Select DTC and the
Specific DTC function.
5. Enter the DTC number
which was set.
6. Operate the vehicle, with
the Conditions for Setting
this DTC, until the scan
tool indicates the
diagnostic Ran.
Does the scan tool indicate the
diagnostic Passed?
Value(s)
Yes
No
System
OK
Go to Step
6
System
OK
--
--
NOTE
6
Notice: In order to avoid damaging
the replacement three-way catalytic
converter, correct the engine misfire
or mechanical fault before replacing
the three-way catalytic converter.
Replace the catalytic converter. Refer
to Catalytic Converter Replacement in
Engine Exhaust.
--
Step
Action
Is the action complete?
Value(s)
Yes
No
PATH: Diagnostics > Diagnostic Routines > Powertrain > Engine Controls - 5.0L
and 5.7L > DTC P0420 Catalyst System Low Efficiency Bank 1 (Under 8600 GVW
(Without C6P))
DTC P0420 Catalyst System Low Efficiency Bank 1 (Under 8600 GVW (Without C6P))
NOTE
Applicable vehicles:
 Chevy Pickup, GMC Pickup, Suburban, Tahoe, Yukon (VIN C/K)
DTC P0420 Catalyst System Low Efficiency Bank 1 (Under 8600 GVW
(without C6P))
Click to Enlarge
Circuit Description
This diagnostic test is designed in order to measure the efficiency of the threeway catalytic converter (TWC) system. Catalytic convertor efficiency is a
measure of its ability to store oxygen after converting the levels of
hydrocarbon (HC), carbon monoxide (CO), and oxides of nitrogen (NOx) to
less harmful gases. The control module is able to evaluate the catalyst
efficiency once the vehicle has met the enable criteria and the vehicle is at idle
instead of the steady cruise speeds used in the past.
Once the conditions for running this diagnostic trouble code (DTC) are met,
the control module commands either a lean or rich air/fuel ratio depending on
the current state of the exhaust oxygen level. The control module issues a rich
command if the exhaust is currently lean, or a lean command if the exhaust is
currently rich. After completion of the first command, a second and opposite
command is issued.
For example, if the control module were to command a rich mixture, the
upstream heated oxygen sensor (HO2S) voltage would increase immediately.
The rich mixture is delayed in reaching the downstream HO2S due to the
conversion process occurring within the converter. The higher the efficiency,
the more the delay before the rich or lean mixture is detected by the
downstream oxygen (O2) sensor. As a result of the lower conversion efficiency
within a damaged or poisoned catalyst, the delay in the rich or lean mixture
reaching the downstream O2 sensor is significantly shorter. This DTC
monitors the amount of time required for both the upstream and downstream
HO2S voltages to cross a calibrated voltage threshold in response to the rich or
lean command.
Conditions for Running the DTC
 No active secondary AIR DTCs
 No active CMP sensor DTCs
 No active ECT sensor DTCs
 No active EGR DTCs
 No active fuel trim DTCs
 No active IAC DTCs
 No active IAT sensor DTCs
 No active MAF sensor DTCs
 No active MAP sensor DTCs
 No active O2 sensor DTCs
 No active transmission DTCs
 No active EVAP system DTCs
 No active TP sensor DTCs
 No active VS sensor DTCs
 No active misfire DTCs
 The engine speed is 1,000 RPM or more for more than 40
seconds since last idle period
 The engine has been running for at least 360 seconds and the
long term fuel trim is stable
 The predicted catalyst temperature is at least 390°C (734°F)

The system is in closed loop
 The BARO is 73 kPa or more
 The IAT is between -7-117°C (20-167° F)
 The ECT is between 75-117°C (167-243° F)
 The engine has been idling for less than 120 seconds
 The actual engine speed is within 100 RPM of the desired idle
speed
Conditions for Setting the DTC
The VCM determines that the oxygen storage capacity of the catalyst has
degraded below a calibrated threshold
Action Taken When the DTC Sets
 The control module illuminates the malfunction indicator
lamp (MIL) the first time the diagnostic runs and fails.
 The control module will set the DTC and records the
operating conditions at the time the diagnostic fails. The
control module stores the failure information in the scan tools
Freeze Frame/Failure Records.
Conditions for Clearing the MIL or DTC
 The control module turns OFF the MIL after 3 consecutive
drive trips when the test has run and passed.
 A history DTC will clear if no fault conditions have been
detected for 40 warm-up cycles. A warm-up cycle occurs
when the coolant temperature has risen 22°C (40°F) from the
startup coolant temperature and the engine coolant reaches a
temperature that is more than 70°C (158°F) during the same
ignition cycle.
 Use a scan tool in order to clear the DTCs.
Diagnostic Aids
The use of fuel with a high sulfur or lead content can degrade a marginal
converter's performance. Be sure to check fuel quality.
An intermittent may be caused by any of the following conditions:
 A poor connection
 Rubbed through wire insulation
 A broken wire inside the insulation
Thoroughly check any circuitry that is suspected of causing the intermittent
complaint. Refer to Intermittents and Poor Connections Diagnosis in Wiring
Systems.
If a repair is necessary, refer to Wiring Repairs or Connector Repairs in Wiring
Systems.
Test Description
The numbers below refer to the step numbers in the diagnostic table.
3. This table checks for conditions that can cause the three-way
catalytic converter efficiency to appear degraded. Inspect and
repair exhaust system as necessary. Refer to Exhaust System
Inspection in Engine Exhaust.
6. Before the three-way catalytic converter is replaced, make sure
that the following conditions are not present:
 Misfire
 High engine oil consumption or coolant consumption
 Retarded spark timing or weak spark
Step
Action
Value(s)
Yes
No
Go to
Step 2
Go to
Powertrain
On Board
Diagnostic
(OBD)
System
Check
WARNING
1
Important: Before clearing the
DTCs, use the scan tool Capture
Info to save the Freeze Frame and
Failure Records for reference. The
control module's data is deleted
once the Clear Info function is used.
--
Did you perform the Powertrain OnBoard Diagnostic (OBD) System
Check?
Are any other DTCs set?
2
3
4
--
1. Check the exhaust system
for the following
conditions:
 Leaks
 Loose or missing
hardware
2. Repair as necessary.
Refer to Exhaust System
Inspection in Engine
Exhaust.
Did you find a problem?
--
1. Verify that the correct
original equipment threeway catalytic converter is
--
Go to the
applicable
DTC
Go to Step
table
3
Go to
Step 5
Go to Step
4
Go to
Step 5
Go to Step
6
Step
5
Action
installed.
2. Check the converter for
the following:
 Dents
 Severe
discoloration
 Holes
3. Ensure that the oxygen
sensors are properly
installed and that the
wiring connections are
properly retained and not
damaged.
4. Repair as necessary.
Refer to Exhaust System
Inspection in Engine
Exhaust.
Did you find a problem?
1. Using the scan tool, clear
the DTCs.
2. Start the engine.
3. Allow the engine to idle
until the engine reaches
normal operating
temperature.
4. Select DTC and the
Specific DTC function.
5. Enter the DTC number
which was set.
6. Operate the vehicle, with
the Conditions for Setting
this DTC, until the scan
tool indicates the
diagnostic Ran.
Does the scan tool indicate the
diagnostic Passed?
Value(s)
Yes
No
System
OK
Go to Step
6
System
OK
--
--
NOTE
6
-Notice: In order to avoid damaging
the replacement three-way catalytic
Step
Action
Value(s)
Yes
No
converter, correct the engine misfire
or mechanical fault before replacing
the three-way catalytic converter.
Replace the catalytic converter. Refer
to Catalytic Converter Replacement in
Engine Exhaust.
Is the action complete?
PATH: Diagnostics > Diagnostic Routines > Powertrain > Engine Controls - 5.0L
and 5.7L > DTC P0420 Catalyst System Low Efficiency Bank 1 (Single Exhaust)
DTC P0420 Catalyst System Low Efficiency Bank 1 (Single Exhaust)
NOTE
Applicable vehicles:
 Chevy Pickup, GMC Pickup, Suburban, Tahoe, Yukon (VIN C/K)
DTC P0420 Catalyst System Low Efficiency Bank 1 (Single Exhaust)
Click to Enlarge
Circuit Description
This diagnostic test is designed in order to measure the efficiency of the threeway catalytic converter (TWC) system. Catalytic convertor efficiency is a
measure of its ability to store oxygen after converting the levels of
hydrocarbon (HC), carbon monoxide (CO), and oxides of nitrogen (NOx) to
less harmful gases. The control module is able to evaluate the catalyst
efficiency once the vehicle has met the enable criteria and the vehicle is at idle
instead of the steady cruise speeds used in the past.
Once the conditions for running this diagnostic trouble code (DTC) are met,
the control module commands either a lean or rich air/fuel ratio depending on
the current state of the exhaust oxygen level. The control module issues a rich
command if the exhaust is currently lean, or a lean command if the exhaust is
currently rich. After completion of the first command, a second and opposite
command is issued.
For example, if the control module were to command a rich mixture, the
upstream heated oxygen sensor (HO2S) voltage would increase immediately.
The rich mixture is delayed in reaching the downstream HO2S due to the
conversion process occurring within the converter. The higher the efficiency,
the more the delay before the rich or lean mixture is detected by the
downstream oxygen (O2) sensor. As a result of the lower conversion efficiency
within a damaged or poisoned catalyst, the delay in the rich or lean mixture
reaching the downstream O2 sensor is significantly shorter. This DTC
monitors the amount of time required for both the upstream and downstream
HO2S voltages to cross a calibrated voltage threshold in response to the rich or
lean command.
Conditions for Running the DTC
 No active secondary AIR DTCs
 No active CMP sensor DTCs
 No active ECT sensor DTCs
 No active EGR DTCs
 No active fuel trim DTCs
 No active IAC DTCs
 No active IAT sensor DTCs
 No active MAF sensor DTCs
 No active MAP sensor DTCs
 No active O2 sensor DTCs
 No active transmission DTCs
 No active EVAP system DTCs
 No active TP sensor DTCs
 No active VS sensor DTCs
 No active misfire DTCs

The engine speed is 1,000 RPM or more for more than 40
seconds since last idle period
 The engine has been running for at least 360 seconds and the
long term fuel trim is stable
 The predicted catalyst temperature is at least 390°C (734°F)
 The system is in closed loop
 The BARO is 73 kPa or more
 The IAT is between -7-117°C (20°-167° F)
 The ECT is between 75-117°C (167-243° F)
 The engine has been idling for less than 120 seconds
 The actual engine speed is within 100 RPM of the desired idle
speed
Conditions for Setting the DTC
The VCM determines that the oxygen storage capacity of the catalyst has
degraded below a calibrated threshold
Action Taken When the DTC Sets
 The control module illuminates the malfunction indicator
lamp (MIL) the first time the diagnostic runs and fails.
 The control module will set the DTC and records the
operating conditions at the time the diagnostic fails. The
control module stores the failure information in the scan tools
Freeze Frame/Failure Records.
Conditions for Clearing the MIL or DTC
 The control module turns OFF the MIL after 3 consecutive
drive trips when the test has run and passed.
 A history DTC will clear if no fault conditions have been
detected for 40 warm-up cycles. A warm-up cycle occurs
when the coolant temperature has risen 22°C (40°F) from the
startup coolant temperature and the engine coolant reaches a
temperature that is more than 70°C (158°F) during the same
ignition cycle.
 Use a scan tool in order to clear the DTCs.
Diagnostic Aids
The use of fuel with a high sulfur or lead content can degrade a marginal
converter's performance. Be sure to check fuel quality.
An intermittent may be caused by any of the following conditions:
 A poor connection
 Rubbed through wire insulation
 A broken wire inside the insulation
Thoroughly check any circuitry that is suspected of causing the intermittent
complaint. Refer to Intermittents and Poor Connections Diagnosis in Wiring
Systems.
If a repair is necessary, refer to Wiring Repairs or Connector Repairs in Wiring
Systems.
Test Description
The numbers below refer to the step numbers in the diagnostic table.
3. This table checks for conditions that can cause the three-way
catalytic converter efficiency to appear degraded. Inspect and
repair exhaust system as necessary. Refer to Exhaust System
Inspection in Engine Exhaust.
6. Before the three-way catalytic converter is replaced, make sure
that the following conditions are not present:
 Misfire
 High engine oil consumption or coolant consumption
 Retarded spark timing or weak spark
Step
Action
Value(s)
Yes
No
Go to
Step 2
Go to
Powertrain
On Board
Diagnostic
(OBD)
System
Check
WARNING
1
Important: Before clearing the
DTCs, use the scan tool Capture
Info to save the Freeze Frame and
Failure Records for reference. The
control module's data is deleted
once the Clear Info function is used.
--
Did you perform the Powertrain OnBoard Diagnostic (OBD) System
Check?
Are any other DTCs set?
2
3
--
1. Check the exhaust system
for the following
conditions:
 Leaks
 Loose or missing
hardware
2. Repair as necessary.
Refer to Exhaust System
Inspection in Engine
Exhaust.
Did you find a problem?
Go to the
applicable
DTC
Go to Step
table
3
--
Go to
Step 5
Go to Step
4
Step
Action
Value(s)
4
1. Verify that the correct
original equipment threeway catalytic converter is
installed.
2. Check the converter for
the following:
 Dents
 Severe
discoloration
 Holes
3. Ensure that the oxygen
sensors are properly
installed and that the
wiring connections are
properly retained and not
damaged.
4. Repair as necessary.
Refer to Exhaust System
Inspection in Engine
Exhaust.
Did you find a problem?
--
1. Using the scan tool, clear
the DTCs.
2. Start the engine.
3. Allow the engine to idle
until the engine reaches
normal operating
temperature.
4. Select DTC and the
Specific DTC function.
5. Enter the DTC number
which was set.
6. Operate the vehicle, with
the Conditions for Setting
this DTC, until the scan
tool indicates the
diagnostic Ran.
Does the scan tool indicate the
diagnostic Passed?
--
5
Yes
No
Go to
Step 5
Go to Step
6
System
OK
Go to Step
6
Step
Action
Value(s)
Yes
No
System
OK
--
NOTE
6
Notice: In order to avoid damaging
the replacement three-way catalytic
converter, correct the engine misfire
or mechanical fault before replacing
the three-way catalytic converter.
--
Replace the catalytic converter. Refer
to Catalytic Converter Replacement in
Engine Exhaust.
Is the action complete?
Trouble Code: P0420 (5.7L V8 VIN R
Auto)
Catalyst System Low Efficiency (Bank 1)
Print this code data
Number of Trips to Set Code: 1
OBD II Monitor Type: CCM Details
Indicators: MIL Details
 CAT Details
 MIL Details
Trouble Code Conditions:
DTC P0101-P0103, P0106-P0108, P0112, P0113, P0117, P0118, P0125,
P0131, P0132-P0138, P0140, P0141, P0151-P0158, P0160, P0161, P0171P0175, P0200, P0300, P0325, P0327, P0335, P0336, P0341, P0343, P0351P0358, P0443-P0449, P0502, P0503, P0506, P0507, P1120, P1125, P1133,
P1134, P1153, P1154, P1220, P1221, P1275, P1276, P1280-P1286, P1441,
P1514, P1518 not set, engine started, engine runtime over 6 minutes, engine
speed over 1000 rpm for 32-40 since last idle period, BARO sensor over 72
kPa, ECT sensor more than 167ºF, IAT sensor over 16ºF, MAF sensor from
15-50 g/sec, Catalyst Temperature over 840ºF, engine running at idle speed for
under 2 minutes with the Actual idle speed within 100-125 rpm of the Desired
idle speed, then vehicle driven to 22-85 mph in closed loop, TP angle over 2%
on 7.4L V8, Long Term fuel trim stable, any change in engine load less than
10%, and the PCM detected the Bank 1 Catalyst was degraded.
Possible Causes:
 Air leaks at the exhaust manifold or in the exhaust pipes
 Base engine problems (i.e., high engine oil or coolant usage)
 Catalytic converter is damaged, contaminated or has failed

Continuous engine misfire conditions, or weak or low coil
output
 Front HO2S or rear HO2S is contaminated with fuel or
moisture
 Rear HO2S is loose in the mounting hole (check it for a leak)
 Front HO2S older (aged) than the rear HO2S (HO2S-12 is
lazy)
 TSB 81-65-37 contains a repair procedure for this code
1998 GMC C1500 Suburban - Powertrain - Engine Controls - 5.0L and
5.7L - DTC P0420 Catalyst System Low Efficiency Bank 1 (Over 8600
GVW (C6P))1998 GMC C1500 Suburban - Powertrain - Engine Controls 5.0L and 5.7L - DTC P0420 Catalyst System Low Efficiency Bank 1
(Single Exhaust)1998 GMC C1500 Suburban - Powertrain - Engine
Controls - 5.0L and 5.7L - DTC P0420 Catalyst System Low Efficiency
Bank 1 (Under 8600 GVW (Without C6P))
PATH: Diagnostics > Diagnostic Routines > Powertrain > Engine Controls - 5.0L
and 5.7L > DTC P0430 Catalyst System Low Efficiency Bank 2 (Over 8600 GVW
C6P)
DTC P0430 Catalyst System Low Efficiency Bank 2 (Over 8600 GVW C6P)
NOTE
Applicable vehicles:
 Chevy Pickup, GMC Pickup, Suburban, Tahoe, Yukon (VIN C/K)
DTC P0430 Catalyst System Low Efficiency Bank 2 (Over 8600 GVW
C6P)
Click to Enlarge
Circuit Description
This diagnostic test is designed in order to measure the efficiency of the threeway catalytic converter (TWC) system. Catalytic convertor efficiency is a
measure of its ability to store oxygen after converting the levels of
hydrocarbon (HC), carbon monoxide (CO), and oxides of nitrogen (NOx) to
less harmful gases. The control module is able to evaluate the catalyst
efficiency once the vehicle has met the enable criteria and the vehicle is at idle
instead of the steady cruise speeds used in the past.
Once the conditions for running this diagnostic trouble code (DTC) are met,
the control module commands either a lean or rich air/fuel ratio depending on
the current state of the exhaust oxygen level. The control module issues a rich
command if the exhaust is currently lean, or a lean command if the exhaust is
currently rich. After completion of the first command, a second and opposite
command is issued.
For example, if the control module were to command a rich mixture, the
upstream heated oxygen sensor (HO2S) voltage would increase immediately.
The rich mixture is delayed in reaching the downstream HO2S due to the
conversion process occurring within the converter. The higher the efficiency,
the more the delay before the rich or lean mixture is detected by the
downstream oxygen (O2) sensor. As a result of the lower conversion efficiency
within a damaged or poisoned catalyst, the delay in the rich or lean mixture
reaching the downstream O2 sensor is significantly shorter. This DTC
monitors the amount of time required for both the upstream and downstream
HO2S voltages to cross a calibrated voltage threshold in response to the rich or
lean command.
Conditions for Running the DTC
 No active secondary AIR DTCs
 No active CMP sensor DTCs
 No active ECT sensor DTCs
 No active EGR DTCs
 No active fuel trim DTCs
 No active IAC DTCs
 No active IAT sensor DTCs
 No active MAF sensor DTCs
 No active MAP sensor DTCs
 No active O2 sensor DTCs
 No active transmission DTCs
 No active EVAP system DTCs
 No active TP sensor DTCs
 No active VS sensor DTCs
 No active misfire DTCs
 The engine speed is 1,000 RPM or more for more than 40
seconds since last idle period
 The engine has been running for at least 360 seconds and the
long term fuel trim is stable
 The predicted catalyst temperature is at least 390°C (734°F)
 The system is in closed loop
 The BARO is 73 kPa or more
 The IAT is between -7-117°C (20°-167° F)
 The ECT is between 75-117°C (167-243° F)
 The engine has been idling for less than 120 seconds
 The actual engine speed is within 100 RPM of the desired idle
speed
Conditions for Setting the DTC
The VCM determines that the oxygen storage capacity of the catalyst has
degraded below a calibrated threshold
Action Taken When the DTC Sets
 The control module illuminates the malfunction indicator
lamp (MIL) the first time the diagnostic runs and fails.
 The control module will set the DTC and records the
operating conditions at the time the diagnostic fails. The
control module stores the failure information in the scan tools
Freeze Frame/Failure Records.
Conditions for Clearing the MIL or DTC
 The control module turns OFF the MIL after 3 consecutive
drive trips when the test has run and passed.
 A history DTC will clear if no fault conditions have been
detected for 40 warm-up cycles. A warm-up cycle occurs
when the coolant temperature has risen 22°C (40°F) from the
startup coolant temperature and the engine coolant reaches a
temperature that is more than 70°C (158°F) during the same
ignition cycle.
 Use a scan tool in order to clear the DTCs.
Diagnostic Aids
The use of fuel with a high sulphur or lead content can degrade a marginal
converter's performance. Be sure to check the fuel quality.
Test Description
The numbers below refer to the step numbers in the diagnostic table.
3. This table checks for conditions that can cause the three-way
catalytic converter efficiency to appear degraded. Inspect and
repair exhaust system as necessary. Refer to Exhaust System
Inspection
6. Before the three-way catalytic converter is replaced, make sure
that the following conditions are not present:
 Misfire
 High engine oil consumption or coolant consumption
 Retarded spark timing or weak spark
Step
Action
Value(s)
Yes
No
Go to
Step 2
Go to
Powertrain
On Board
Diagnostic
(OBD)
System
Check
WARNING
1
Important: Before clearing the
DTCs, use the scan tool Capture
Info to save the Freeze Frame and
Failure Records for reference. The
control module's data is deleted
once the Clear Info function is used.
--
Did you perform the Powertrain OnBoard Diagnostic (OBD) System
Check?
Are any other DTCs set?
2
--
Go to the
applicable
DTC
Go to Step
table
3
Step
Action
Value(s)
3
1. Check exhaust system for
the following:
 Leaks
 Loose or missing
hardware
2. Repair as necessary.
Refer to Exhaust System
Inspection in Engine
Exhaust.
Did you find a problem?
--
1. Verify that the correct
original equipment threeway catalytic converter is
installed.
2. Check the converter for
the following:
 Dents
 Severe
discoloration
 Holes
3. Ensure that the oxygen
sensors are properly
installed and that the
wiring connections are
properly retained and not
damaged.
4. Repair as necessary.
Refer to Exhaust System
Inspection .
Did you find a problem?
--
1. Using the scan tool, clear
the DTCs.
2. Start the engine.
3. Allow the engine to idle
until the engine reaches
normal operating
temperature.
4. Select DTC and the
Specific DTC function.
5. Enter the DTC number
that was set.
--
4
5
Yes
No
Go to
Step 5
Go to Step
4
Go to
Step 5
Go to Step
6
System
OK
Go to Step
6
Step
Action
6. Operate the vehicle,
within the Conditions for
Setting this DTC, until
the Scan Tool indicates
the diagnostic Ran.
Does the Scan tool indicate the
diagnostic Passed?
Value(s)
Yes
No
System
OK
--
NOTE
6
Notice: In order to avoid damaging
the replacement three-way catalytic
converter, correct the engine misfire
or mechanical fault before replacing
the three-way catalytic converter.
Replace the catalytic converter. Refer
to Catalytic Converter Replacement in
Engine Exhaust.
Is the action complete?
--
PATH: Diagnostics > Diagnostic Routines > Powertrain > Engine Controls - 5.0L
and 5.7L > DTC P0430 Catalyst System Low Efficiency Bank 2 (Under 8600 GVW
without C6P)
DTC P0430 Catalyst System Low Efficiency Bank 2 (Under 8600 GVW without C6P)
NOTE
Applicable vehicles:
 Chevy Pickup, GMC Pickup, Suburban, Tahoe, Yukon (VIN C/K)
DTC P0430 Catalyst System Low Efficiency Bank 2 (Under 8600 GVW
without C6P)
Click to Enlarge
Circuit Description
This diagnostic test is designed in order to measure the efficiency of the threeway catalytic converter (TWC) system. Catalytic convertor efficiency is a
measure of its ability to store oxygen after converting the levels of
hydrocarbon (HC), carbon monoxide (CO), and oxides of nitrogen (NOx) to
less harmful gases. The control module is able to evaluate the catalyst
efficiency once the vehicle has met the enable criteria and the vehicle is at idle
instead of the steady cruise speeds used in the past.
Once the conditions for running this diagnostic trouble code (DTC) are met,
the control module commands either a lean or rich air/fuel ratio depending on
the current state of the exhaust oxygen level. The control module issues a rich
command if the exhaust is currently lean, or a lean command if the exhaust is
currently rich. After completion of the first command, a second and opposite
command is issued.
For example, if the control module were to command a rich mixture, the
upstream heated oxygen sensor (HO2S) voltage would increase immediately.
The rich mixture is delayed in reaching the downstream HO2S due to the
conversion process occurring within the converter. The higher the efficiency,
the more the delay before the rich or lean mixture is detected by the
downstream oxygen (O2) sensor. As a result of the lower conversion efficiency
within a damaged or poisoned catalyst, the delay in the rich or lean mixture
reaching the downstream O2 sensor is significantly shorter. This DTC
monitors the amount of time required for both the upstream and downstream
HO2S voltages to cross a calibrated voltage threshold in response to the rich or
lean command.
Conditions for Running the DTC
 No active secondary AIR DTCs
 No active CMP sensor DTCs
 No active ECT sensor DTCs
 No active EGR DTCs
 No active fuel trim DTCs
 No active IAC DTCs
 No active IAT sensor DTCs
 No active MAF sensor DTCs
 No active MAP sensor DTCs
 No active O2 sensor DTCs
 No active transmission DTCs
 No active EVAP system DTCs
 No active TP sensor DTCs
 No active VS sensor DTCs
 No active misfire DTCs
 The engine speed is 1,000 RPM or more for more than 40
seconds since last idle period
 The engine has been running for at least 360 seconds and the
long term fuel trim is stable
 The predicted catalyst temperature is at least 390°C (734°F)
 The system is in closed loop
 The BARO is 73 kPa or more
 The IAT is between -7-117°C (20°-167° F)
 The ECT is between 75-117°C (167-243° F)
 The engine has been idling for less than 120 seconds
 The actual engine speed is within 100 RPM of the desired idle
speed
Conditions for Setting the DTC
The VCM determines that the oxygen storage capacity of the catalyst has
degraded below a calibrated threshold
Action Taken When the DTC Sets
 The control module illuminates the malfunction indicator
lamp (MIL) the first time the diagnostic runs and fails.
 The control module will set the DTC and records the
operating conditions at the time the diagnostic fails. The
control module stores the failure information in the scan tools
Freeze Frame/Failure Records.
Conditions for Clearing the MIL or DTC
 The control module turns OFF the MIL after 3 consecutive
drive trips when the test has run and passed.
 A history DTC will clear if no fault conditions have been
detected for 40 warm-up cycles. A warm-up cycle occurs
when the coolant temperature has risen 22°C (40°F) from the
startup coolant temperature and the engine coolant reaches a
temperature that is more than 70°C (158°F) during the same
ignition cycle.
 Use a scan tool in order to clear the DTCs.
Diagnostic Aids
The use of fuel with high sulphur or lead content can degrade a marginal
converter's performance. Be sure to check the fuel quality.
An intermittent may be caused by any of the following conditions:
 A poor connection
 Rubbed through wire insulation
 A broken wire inside the insulation
Thoroughly check any circuitry that is suspected of causing the intermittent
complaint. Refer to Intermittents and Poor Connections Diagnosis in Wiring
Systems.
If a repair is necessary, refer to Wiring Repairs or Connector Repairs in Wiring
Systems.
Test Description
The numbers below refer to the step numbers in the diagnostic table.
3. This table checks for conditions that can cause the three-way
catalytic converter efficiency to appear degraded. Inspect and
repair exhaust system as necessary. Refer to Exhaust System
Inspection
6. Before the three-way catalytic converter is replaced, make sure
that the following conditions are not present:
 Misfire
 High engine oil consumption or coolant consumption
 Retarded spark timing or weak spark
Step
Action
Value(s)
Yes
No
Go to
Step 2
Go to
Powertrain
On Board
Diagnostic
(OBD)
System
Check
WARNING
1
Important: Before clearing the
DTCs, use the scan tool Capture
Info to save the Freeze Frame and
Failure Records for reference. The
--
Step
Action
Value(s)
Yes
No
control module's data is deleted
once the Clear Info function is used.
Did you perform the Powertrain OnBoard Diagnostic (OBD) System
Check?
Are any other DTCs set?
2
3
4
--
1. Check exhaust system for
the following:
 Leaks
 Loose or missing
hardware
2. Repair as necessary.
Refer to Exhaust System
Inspection in Engine
Exhaust.
Did you find a problem?
--
1. Verify that the correct
original equipment threeway catalytic converter is
installed.
2. Check the converter for
the following:
 Dents
 Severe
discoloration
 Holes
3. Ensure that the oxygen
sensors are properly
installed and that the
wiring connections are
properly retained and not
damaged.
4. Repair as necessary.
Refer to Exhaust System
Inspection .
Did you find a problem?
--
Go to the
applicable
DTC
Go to Step
table
3
Go to
Step 5
Go to Step
4
Go to
Step 5
Go to Step
6
Step
Action
Value(s)
5
1. Using the scan tool, clear
the DTCs.
2. Start the engine.
3. Allow the engine to idle
until the engine reaches
normal operating
temperature.
4. Select DTC and the
Specific DTC function.
5. Enter the DTC number
that was set.
6. Operate the vehicle,
within the Conditions for
Setting this DTC, until
the Scan Tool indicates
the diagnostic Ran.
Does the Scan tool indicate the
diagnostic Passed?
--
Yes
No
System
OK
Go to Step
6
System
OK
--
NOTE
6
Notice: In order to avoid damaging
the replacement three-way catalytic
converter, correct the engine misfire
or mechanical fault before replacing
the three-way catalytic converter.
--
Replace the catalytic converter. Refer
to Catalytic Converter Replacement in
Engine Exhaust.
Is the action complete?
Trouble Code: P0430 (5.7L V8 VIN R
Auto)
Catalyst System Low Efficiency (Bank 2)
Number of Trips to Set Code: 1
OBD II Monitor Type: CCM Details
Indicators: MIL Details
 CAT Details
 MIL Details
Print this code data
Trouble Code Conditions:
DTC P0101-P0103, P0106-P0108, P0112-P0118, P0125, P0131, P0132P0138, P0140, P0141, P0151-P0158, P0160, P0161, P0171-P0175, P0200,
P0300, P0325, P0327, P0335, 336, P0341, P0343, P0351-P0358, P0443P0449, P0502, P0503, P0506, P0507, P1120, P1125, P1133, P1134, P1153,
P1154, P1220, P1221, P1275, P1276, P1280-P1286, P1441, P1514-P1518 not
set, engine runtime over 6 minutes, ECT sensor over 167ºF, BARO sensor over
72 kPa, IAT sensor over 16ºF, MAF sensor from 15-50 g/sec, Catalyst
Temperature over 840ºF, engine running at idle speed for 2 minutes with
Actual idle speed within 100-125 rpm of the Desired idle speed, vehicle driven
to 22-85 mph, less than a 10% change in engine load, fuel trim stable, and the
PCM detected the Catalyst was degraded.
Possible Causes:
 Air leaks at the exhaust manifold or in the exhaust pipes
 Base engine problems (i.e., high engine oil or coolant usage)
 Catalytic converter is damaged, contaminated or has failed
 Continuous engine misfire conditions, or weak or low coil
output
 Front HO2S or rear HO2S is contaminated with fuel or
moisture
 Rear HO2S is loose in the mounting hole (check it for a leak)
1998 GMC C1500 Suburban - Powertrain - Engine Controls - 5.0L and
5.7L - DTC P0430 Catalyst System Low Efficiency Bank 2 (Over 8600
GVW C6P)1998 GMC C1500 Suburban - Powertrain - Engine Controls 5.0L and 5.7L - DTC P0430 Catalyst System Low Efficiency Bank 2
(Under 8600 GVW without C6P)