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0 Service Information Document ID: 2603119 DTC P205B-P205D Diagnostic Instructions Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Review Strategy Based Diagnosis for an overview of the diagnostic approach. Diagnostic Procedure Instructions provides an overview of each diagnostic category. DTC Descriptors DTC P205B Reductant Tank Temperature Sensor Performance DTC P205C Reductant Tank Temperature Sensor Circuit Low Voltage DTC P205D Reductant Tank Temperature Sensor Circuit High Voltage Circuit/System Description The reductant level/temperature sensor is a solid-state device that provides the engine control module (ECM) with information on reductant level and temperature. The level/temperature sensor receives system voltage directly from the underhood electrical center and ground through a chassis ground circuit. The level sensor consists of three sensing elements. Reductant level sensor 3 is highest, reductant level sensor 2 is located between sensor 1 and 3. Reductant level sensor 1 is located at low reductant level. Reductant level sensor 3 is located at less than half range of the DEF tank level. The scan tool will display Active when the level sensors are in contact with reductant and Inactive when not in contact with reductant. An integrated temperature sensor monitors reductant temperature. Reductant level and temperature signals are processed within the sensor and supplied to the ECM as serial data messages. The ECM will set a DTC when it detects an invalid level or temperature serial data message from the sensor. Conditions for Running the DTC DTC P205D is not set. - for P205B only The ignition is Off for 8 hours. The ECM monitors the ECT, Exhaust Gas Temperature (EGT) 2, and EGT 4 for the coldest and warmest of the three sensors. The difference between the coldest and warmest should be less than 7°C (45°F). The engine speed is greater than 600 RPM. The battery voltage is greater than 11 V. The DTCs run once per drive cycle when the above conditions are met for greater than 20 s. Conditions for Setting the DTC P205B The ECM receives a serial data message from the reductant sensor module that the reductant temperature is not within −35 to +35°C (−31 to +95°F) of the fuel pump temperature sensor for greater than 3 s. Or The ECM receives a serial data message from the reductant sensor module that the reductant temperature is not within −55 to +155°C (−67 to +311°F) for greater than 3 s. P205C The ECM receives a serial data message from the reductant sensor module that the reductant temperature is less than −55°C (−67°F) for greater than 3 s. P205D The ECM receives a serial data message from the reductant sensor module that the reductant temperature is greater than 160°C (320°F) for greater than 3 s. Action Taken When the DTC Sets DTCs P205B and P205D are Type B DTCs. DTC P205C is a Type A DTC. The ECM commands the engine to operate in Reduced Engine Power mode. The driver information center may display the Engine Power Is Reduced message. Conditions for Clearing the DTC DTCs P205B and P205D are Type B DTCs. DTC P205C is a Type A DTC. Reference Information Schematic Reference Engine Controls Schematics Connector End View Reference Component Connector End Views Description and Operation Diesel Exhaust Fluid (DEF) Warning Strategy Exhaust Aftertreatment System Description Electrical Information Reference Circuit Testing Connector Repairs Testing for Intermittent Conditions and Poor Connections Wiring Repairs Scan Tool Reference Control Module References for scan tool information Circuit/System Verification 1. Ignition On. 2. Verify DTC UXXXX is not set. o If a DTC is set Refer to Diagnostic Trouble Code (DTC) List - Vehicle o If no DTC is set 3. Observe the scan tool Reductant Temperature. The reading should be warmer than −55°C (−67°F) and colder than 160°C (320°F). o If not within the specified range Refer to Circuit/System Testing. o If within the specified range 4. Compare the scan tool Ambient Air Temperature to the Reductant Temperature. The readings should be within 35°C (95°F). o If not within the specified range Refer to Circuit/System Testing. o If within the specified range 5. Operate the vehicle within the Conditions for Running. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data. 6. Verify a DTC does not set. o If any DTC sets Refer to Circuit/System Testing. o If no DTC sets 7. All OK. Circuit/System Testing 1. Ignition Off and all vehicle systems Off, disconnect the harness connector at the reductant temperature sensor side of the B212 Reductant Sensor Module . It may take up to 2 minutes for all vehicle systems to power down. Note: The reductant tank level must be at least 33% full and the reductant temperature must be greater than -5°C (23°F) to ensure accurate resistance readings. 2. Verify the resistance of the reductant temperature sensor between the harness connector circuit terminal 2 and circuit terminal 3 is within the range specified in the Temperature Versus Resistance table. o If not within the specified range Replace the B214 Reductant Temperature Sensor. o If within the specified range 3. Replace the B212 Reductant Sensor Module. Repair Instructions Emission Reduction Fluid Tank Reservoir Replacement for B214 Reductant Temperature Sensor Level and Temperature Emission Reduction Fluid Tank Module Replacement for B212 Reductant Sensor Module Perform the scan tool Reductant System Reset procedure after replacing the B214 Reductant Temperature Sensor. Repair Verification 1. Install any components or connectors that have been removed or replaced during diagnosis. 2. Perform any adjustment, programming, or setup procedures that are required when a component or module is removed or replaced. 3. Clear the DTCs. 4. Ignition Off, all vehicle systems Off, this may take up to 2 minutes. Note: The diesel exhaust fluid (DEF) and ambient air temperatures must be greater than −7°C (19°F) before proceeding with this procedure. o Exhaust Gas Temperature (EGT) sensor 2 must be less than 200°C (392°F) prior to running the Rductant System Leak Test. 5. Ignition On, command the Reductant System Leak Test On with a scan tool. Allow the pressure to build for 30 s. Observe the scan tool Reductant Pressure sensor parameter. The reading should be between 400–600 kPa (58–94 psi) and there should be no leaks in the system. 6. Ignition Off, all vehicle systems Off, this may take up to 2 minutes. 7. Engine idling for 30 s. 8. Ignition Off, all vehicle systems Off, this may take up to 2 minutes. 9. Ignition On. 10. Perform the Reductant System Data Reset with a scan tool in order to clear the DEF lamp. o If the DEF lamp does not turn Off o A condition with the system still exists. o If the DEF lamp turns Off 11. Perform the Reductant System Malfunction Warning Test with a scan tool in order to clear the Service Emission System message, if displayed. o If the Service Emission System message does not turn Off A condition with the system still exists. o If the Service Emission System message turns Off 12. All OK. © 2015 General Motors. All rights reserved. xTooltipElement 0 Service Information Document ID: 2475470 DTC P0102 or P0103 Diagnostic Instructions Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Review Strategy Based Diagnosis for an overview of the diagnostic approach. Diagnostic Procedure Instructions provide an overview of each diagnostic category. DTC Descriptors DTC P0102 Mass Air Flow (MAF) Sensor Circuit Low Frequency DTC P0103 Mass Air Flow (MAF) Sensor Circuit High Frequency Diagnostic Fault Information Circuit Ignition Voltage Signal Typical Scan Tool Data Short to Ground P0103 P0103 Open/High Resistance P0103 P0103 Short to Voltage P103 P0103 Signal Performance P0103 P0103 MAF Sensor Circuit Short to Ground Open Short to Voltage Operating Conditions: Engine running at idle, engine coolant temperature (ECT) sensor warmer than 60°C (140°F) Parameter Normal Range: 10–40 g/s Operating Conditions: Engine running at idle, ECT sensor colder than 60°C (140°F) Parameter Normal Range: 30–40 g/s Ignition Voltage Signal Low Reference Circuit/System Description 0.0 g/s 0.0 g/s — 0.0 g/s 0.0 g/s — — 0.0 g/s — The mass air flow (MAF) sensor is integrated with the intake air temperature (IAT) sensor 2. The MAF sensor is an air flow meter that measures the amount of air entering the engine. The engine control module (ECM) uses the MAF sensor signal to provide the correct fuel delivery for all engine speeds and loads. A small quantity of air entering the engine indicates a deceleration or idle condition. A large quantity of air entering the engine indicates an acceleration or high load condition. The ECM monitors the exhaust gas recirculation (EGR) flow when the EGR valve is commanded ON. The ECM compares the desired MAF to the actual MAF, if the difference is less than or greater than a calibrated threshold level the amount of detected EGR flow is out of range and an EGR DTC will set. The ECM applies 5 V to the MAF sensor on the MAF sensor signal circuit. The sensor uses the voltage to produce a frequency based on the inlet airflow through the sensor bore. The frequency varies in a range of approximately 2,300 Hz at idle to near 9,000 Hz at maximum engine load, depending on engine coolant temperature (ECT). When the ECT reaches 60°C (140°F) the ECM can command the exhaust gas recirculation (EGR) valve ON, and a lower frequency and g/s value will be indicated on the scan tool. Conditions for Running the DTC P0102 DTCs P0335 or P0336 are not set. The engine is running for longer than 10 s. This DTC runs continuously when the enabling conditions are met. P0103 DTCs P0335 or P0336 are not set. The ignition is ON. This DTC runs continuously when the enabling conditions are met. Conditions for Setting the DTC P0102 The ECM detects that the MAF sensor is less than 1.08 g/s for greater than 3 s. P0103 The ignition is ON, and the ECM detects a fault on the MAF sensor circuits. OR The engine is running, and the ECM detects that the MAF sensor signal is greater than 625 g/s, for greater than 3 s. Action Taken When the DTC Sets DTCs P0102 and P0103 are Type A DTCs. The ECM commands reduced engine power. The driver information center (DIC) or indicator may display reduced engine power. Diesel particulate filter (DPF) regeneration is inhibited. Conditions for Clearing the DTC DTCs P0102 and P0103 are Type A DTCs. Diagnostic Aids A wide open throttle (WOT) acceleration from a stop should cause the MAF Sensor parameter on the scan tool to increase rapidly. This increase should be from 6–8 g/s at idle to greater than 380 g/s at the time of the 1-2 shift. For an intermittent problem, visually and physically inspect the EGR valve for a possible binding or sticking in the open position. Verify that any electrical aftermarket devices are properly connected and grounded. Refer to Checking Aftermarket Accessories. A faulty EGR valve that does not close or open fully, may set this DTC. Reference Information Schematic Reference Engine Controls Schematics Connector End View Reference Component Connector End Views Electrical Information Reference Circuit Testing Connector Repairs Testing for Intermittent Conditions and Poor Connections Wiring Repairs Powertrain Component Views Powertrain Component Views DTC Type Reference Powertrain Diagnostic Trouble Code (DTC) Type Definitions Scan Tool Reference Control Module References for scan tool information Special Tools EN 38522 Variable Signal Generator For equivalent regional tools, refer to Special Tools. Circuit/System Verification 1. Ignition ON. 2. Verify that DTCs P0106, P0403, or P046C are not set. o If the DTC sets. If any of the DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle. o If no DTC sets. 3. Verify the scan tool MAF Sensor parameter is between 10–40 g/s, depending on the ECT temperature and EGR position. o If not between 10–40 g/s Refer to Circuit/System Testing. o If between 10–40 g/s 4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data. 5. Verify the DTC does not set. o If the DTC sets Refer to Circuit/System Testing. o If the DTC does not set 6. All OK. Circuit/System Testing Note: You must perform the Circuit/System Verification before proceeding with the Circuit/System Testing. You must perform the Diagnostic Repair Verification after completing the Circuit/System Testing. 1. Engine idling, at operating temperature. 1. Command the EGR solenoid to 0 % with a scan tool. 2. Observe the Airflow Leak Equivalence Ratio parameter for 10 s. Verify the parameter stabilizes after 10 s and is between 0.8:1 and 1.2:1. 3. Slowly increase the engine speed until reaching wide open throttle (WOT). 4. Verify the Airflow Leak Equivalence Ratio parameter stabilizes after 10 s and is between 0.8:1 and 1.2:1. o If not stable after 10 s and between 0.8:1 and 1.2:1. Test the charge air cooler system and air inlet system for leaks. Perform the Full System Air Leak Test and the Induction System Smoke Test. Refer to Charge Air Cooler Diagnosis If stable after 10 s and between 0.8:1 and 1.2:1. 2. Verify the exhaust gas recirculation valve is in the closed position, by visual inspection. Refer to Exhaust Gas Recirculation Valve Replacement. o If the exhaust gas recirculation valve is not closed. o Replace the exhaust gas recirculation valve and gaskets. o 3. 4. 5. 6. If the exhaust gas recirculation valve is closed. Ignition OFF, disconnect the harness connector at the (5 Pin) B75B Mass Air Flow/Intake Air Temperature sensor. Ignition OFF and all vehicle systems OFF. It may take up to 2 minutes for all vehicle systems to power down. Test for less than 2 Ω between the mass air flow ground circuit terminal E and ground. o If 2 Ω or greater 1. Ignition OFF, disconnect the harness connector at the K20 Engine Control Module. 2. Test for less than 2 Ω in the ground circuit end to end. If 2 Ω or greater, repair the open or high resistance in the circuit. If less than 2 Ω replace the K20 Engine Control Module. o If less than 2 Ω Ignition ON, verify a test lamp illuminates between the ignition voltage circuit terminal D and ground. o If the test lamp does not illuminate and the circuit fuse is good 1. Ignition OFF, remove the test lamp and remove the fuse for the ignition voltage circuit. 2. Test for less than 2 Ω in the ignition voltage circuit end to end. If 2 Ω or greater, repair the open/high resistance in the circuit. If less than 2 Ω, verify the fuse is not open and there is voltage at the fuse. o If the test lamp does not illuminate and the circuit fuse is open 4. Ignition OFF, remove the test lamp and remove the fuse for the ignition voltage circuit. 5. Test for infinite resistance between the ignition voltage circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance 6. Test for greater than 2 Ω between the ignition voltage circuit terminal D and ground. If less than 2 Ω, repair the short to ground on the circuit. If greater than 2 Ω, test all the components connected to the circuit and repair or replace as necessary. o If the test lamp illuminates Ignition ON, test for 4.8–5.2 V between the mass air flow signal circuit terminal C and ground. o If less than 4.8 V 1. Ignition OFF, disconnect the harness connector at the K20 Engine Control Module. 2. Test for infinite resistance between the signal circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance 3. Test for less than 2 Ω in the signal circuit end to end. If 2 Ω or greater, repair the open/high resistance in the circuit. If less than 2 Ω, replace the K20 Engine Control Module. o If greater than 5.2 V Note: If the signal circuit is shorted to a voltage the engine control module or the sensor may be damaged. 5. Ignition OFF, disconnect the harness connector at the K20 Engine Control Module. 6. Ignition ON, test for less than 1 V between the signal circuit and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the K20 Engine Control Module. o If between 4.8–5.2 V 7. Ignition OFF, connect the leads of the EN 38522 Variable Signal Generator as follows: o Red lead to the signal circuit terminal C at the harness connector o Black lead to ground o Battery voltage supply lead to B+ 8. Set the EN 38522 Variable Signal Generator to the following specifications. o Signal switch to 5 V o Duty Cycle switch to 50 % (Normal) o Frequency switch to 5 KHz 9. Engine idling. 10. Verify the scan tool MAF Sensor parameter is between 4,950–5,050 Hz. o If not between 4,950–5,050 Hz. Replace the K20 Engine Control Module. o If between 4,950–5,050 Hz. 11. Test or replace the (5 Pin) B75B Mass Air Flow/Intake Air Temperature sensor. Repair Instructions Perform the Diagnostic Repair Verification after completing the repair. Perform the scan tool Diesel Particulate Filter (DPF) Regeneration Enable procedure if the DPF Soot Mass is less than 30 g. If the scan tool DPF Soot Mass is 30 g or greater, perform the Diesel Particulate Filter (DPF) Service Regeneration procedure. Mass Airflow Sensor with Intake Air Temperature Sensor Replacement for (5 Pin) Mass Air Flow/Intake Air Temperature sensor replacement Control Module References for ECM replacement, programming, and setup © 2015 General Motors. All rights reserved. xTooltipElement 0 Service Information Document ID: 3416732 DTC P0112 or P0113 Diagnostic Instructions Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Review Strategy Based Diagnosis for an overview of the diagnostic approach. Diagnostic Procedure Instructions provide an overview of each diagnostic category. DTC Descriptors DTC P0112 Intake Air Temperature (IAT) Sensor 1 Circuit Low Voltage DTC P0113 Intake Air Temperature (IAT) Sensor 1 Circuit High Voltage Diagnostic Fault Information IAT Sensor 1 Circuit Short to Ground Open/High Resistance Short to Voltage Signal P0112 P0113 P0113* Low Reference — — * *Internal ECM or sensor damage may occur if the circuit is shorted to B+. Typical Scan Tool Data IAT Sensor 1 Circuit Short to Ground Open Operating Conditions: Ignition ON or Engine Running Parameter Normal Range: −39 to +148°C (−38 to +298°F) Signal 150°C (302°F) −40°C (−40°F) Low Reference — — *Internal ECM or sensor damage may occur if the circuit is shorted to B+ Circuit/System Description Signal Performance P0113, P0101, P111D P111D Short to Voltage −40°C (−40°F)* * The intake air temperature (IAT) sensor 1 is a variable resistor that measures the temperature of the air at the mass air flow (MAF) sensor. The IAT Sensor 1 is part of the mass air flow (MAF/IAT) sensor assembly. The engine control module (ECM) supplies 5 V to the IAT sensor 1 circuit, and a ground for the IAT sensor 1 low reference circuit. The ECM monitors the IAT sensor 1 signal for an excessively high or low voltage, or for a voltage that is not in correlation with the fuel rail temperature sensor start up signal. Conditions for Running the DTC P0112 or P0113 The engine is runnning for longer than 10 s. The DTCs run continuously when the above condition is met. Conditions for Setting the DTC P0112 The IAT Sensor 1 parameter is warmer than 148°C (299°F) for greater than 3 s. This is equal to or less than 0.08 V on the IAT signal circuit as measured by the ECM. P0113 The IAT Sensor 1 parameter is colder than −39°C (−38°F) for greater than 3 s. This is equal to greater than 4.9 V on the IAT signal circuit as measured by the ECM. Action Taken When the DTC Sets DTCs P0112 and P0113 are Type A DTCs. The ECM commands reduced engine power. The driver information center (DIC) or indicator may display reduced engine power. Conditions for Clearing the DTC DTCs P0112 and P0113 are Type A DTCs. Diagnostic Aids With the ignition ON and the engine OFF, if the engine is cold, a properly functioning IAT Sensor 1 will gradually increase the scan tool IAT Sensor 1 parameter. This is due to the heat that is generated by the MAF sensor heating elements. Depending on the ambient temperature, an IAT Sensor 1 signal circuit or low reference circuit that is shorted to the MAF sensor signal circuit can cause a DTC P0113 to set. This condition can cause a rapid fluctuation in the IAT Sensor 1 parameter. The Fuel Rail Temperature Sensor is located at the return line from the fuel rail. The Fuel Rail Temperature Sensor is also know as the Fuel Temperature Sensor 2. If DTC P0103 is also set, check for a disconnected MAF/IAT sensor. Reference Information Schematic Reference Engine Controls Schematics Connector End View Reference Component Connector End Views Electrical Information Reference Circuit Testing Connector Repairs Testing for Intermittent Conditions and Poor Connections Wiring Repairs DTC Type Reference Powertrain Diagnostic Trouble Code (DTC) Type Definitions Scan Tool Reference Control Module References for scan tool information Circuit/System Verification Note: Perform Steps 1 and 2 of this verification procedure only if the ignition has been OFF for 8 hours or more. The vehicle sitting in direct sun light or having the block heater ON will skew the results. 1. Ignition ON, observe the following scan tool parameters. The readings should be within 15°C (27°F) of each other. o IAT Sensor 1 Sensor o Start-Up ECT Sensor o Ambient Air Temp. Sensor 2. Ignition ON, observe the following scan tool parameters. The readings should be within 20°C (36°F) of each other. o IAT Sensor 1 sensor o Ambient Air Temp. Sensor 3. Engine idling, observe the scan tool IAT Sensor 1 parameter. The reading should be between −38 to +148°C (−36 to +298°F) depending on the current ambient temperature and the vehicle operating conditions. 4. Operate the vehicle within the Conditions for Running the DTC to verify that the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data. Circuit/System Testing 1. Ignition OFF, disconnect the harness connector at the mass air flow B75B MAF/IAT sensor. 2. Ignition OFF and all vehicle systems OFF. It may take up to 2 minutes for all vehicle systems to power down. Test for less than 5 Ω between the IAT Sensor 1 low reference circuit terminal A and ground. o If greater than the specified range, test the IAT Sensor 1 low reference circuit for an open/high resistance. If the circuit tests normal, replace the K20 ECM. 3. Ignition OFF and all vehicle systems OFF. It may take up to 2 minutes for all vehicle systems to power down. Test for less than 5 Ω between the MAF sensor low reference circuit terminal E and ground. o If greater than the specified range, test the MAF sensor low reference circuit for an open/high resistance. If the circuit tests normal, replace the K20 ECM. 4. Ignition ON, verify the scan tool IAT Sensor 1 parameter is colder than −39°C (−38°F). o If warmer than the specified range, test the IAT Sensor 1 signal circuit for a short to ground. If the circuit tests normal, replace the K20 ECM. Note: If a short to voltage is found on the IAT Sensor 1 signal circuit, the 3A fuse in the jumper wire will open. 5. Install a 3A fused jumper wire between the IAT Sensor 1 signal circuit terminal B and ground. Verify the scan tool IAT Sensor 1 parameter is warmer than 148°C (298°F). If colder than the specified range, test the IAT Sensor 1 circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the K20 ECM. 6. If all circuits test normal, test or replace the B75B MAF/IAT sensor. o Component Testing Ignition OFF, disconnect the harness connector at the B75B MAF/IAT sensor. Measure the resistance between the IAT Sensor 1 signal terminal B and the IAT Sensor 1 low reference circuit terminal A at the IAT Sensor 1. Compare the value to the Temperature Vs Resistance table. Verify the resistance is within 5 % of the specification. Refer to Temperature Versus Resistance IAT Sensor 1 table. Repair Instructions Mass Airflow Sensor with Intake Air Temperature Sensor Replacement for intake air temperature (IAT 1) sensor replacement Control Module References for ECM replacement, programming, and setup Repair Verification 1. Install any components or connectors that have been removed or replaced during diagnosis. 2. Perform any adjustment, programming, or setup procedures that are required when a component or module is removed or replaced. 3. Clear the DTCs. 4. Ignition OFF and all vehicle systems OFF. It may take up to 2 minutes for all vehicle systems to power down 5. Duplicate the Conditions for Running the DTC and use the Freeze Frame/Failure Records, if applicable, in order to verify the DTC does not reset. If the DTC resets or another DTC is present, refer to Diagnostic Trouble Code (DTC) List - Vehicle and perform the appropriate diagnostic procedure. 6. Perform the Diesel Particulate Filter (DPF) Service Regeneration. © 2015 General Motors. All rights reserved. xTooltipElement 0 Service Information Document ID: 2614856 DTC P125A or P125B Diagnostic Instructions Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Review Strategy Based Diagnosis for an overview of the diagnostic approach. Diagnostic Procedure Instructions provides an overview of each diagnostic category. DTC Descriptor DTC P125A Fuel Pressure Regulator 2 High Control Circuit Low Voltage DTC P125B Fuel Pressure Regulator 2 High Control Circuit High Voltage Diagnostic Fault Information Circuit Short to Ground Open/High Resistance Short to Voltage Signal Performance Fuel Rail Pressure Solenoid Supply Voltage P125A P2294 P125B P128E, P0087, P0088 Fuel Rail Pressure Solenoid Low Reference P2295 P2294 P2296 P128E, P0087, P0088 Typical Scan Tool Data Fuel Press. Reg 2 High Ctrl. Ckt. Short Gnd Test Status Circuit Short to Ground Open Operating Conditions: Engine Running Parameter Normal Range: OK/Not Run Fuel Rail Pressure Solenoid Supply Voltage Fault OK/Not Run Fuel Press. Reg 2 High Ctrl. Ckt. Short Volts Test Status Circuit Short to Ground Open Operating Conditions: Engine Running Parameter Normal Range: OK/Not Run Fuel Rail Pressure Solenoid Supply Voltage Circuit/System Description OK/Not Run Short to Voltage OK/Not Run Short to Voltage OK/Not Run Fault The engine control module (ECM) controls the fuel rail pressure by controlling fuel pressure regulator 1 and fuel pressure regulator 2 simultaneously to achieve the desired fuel rail pressure. Fuel pressure regulator 2 is located on the front of the left hand side fuel rail and is used to control the amount of fuel that is bypassed to the fuel return system. Fuel pressure regulator 2 also allows fuel pressure leak down when the engine is OFF. Conditions for Running the DTC Engine speed is greater than 600 RPM. Battery voltage is greater than 11 V. Conditions for Setting the DTC DTC P125A The ECM detects low voltage on the supply voltage circuit of fuel pressure regulator 2 for greater than 0.5 s. DTC P125B The ECM detects high voltage on the supply voltage circuit of fuel pressure regulator 2 for greater than 0.1 s. Action Taken When the DTC Sets DTC P125A is Type A DTC DTC P125B is Type B DTC The ECM commands the engine to operate in the Reduced Engine Power mode. The message center displays Engine Power Is Reduced. Conditions for Clearing the DTC DTC P125A is Type A DTC DTC P125B is Type B DTC Diagnostic Aids A failure in the fuel pressure regulator 2 system could cause a crank no start condition. Intermittent or poor connections may cause this DTC to set. If the fuel system pressure is actually too high, a fuel knock condition may exist. Reference Information Schematic Reference Engine Controls Schematics Connector End View Reference Component Connector End Views Description and Operation Fuel System Description Electrical Information Reference Circuit Testing Connector Repairs Testing for Intermittent Conditions and Poor Connections Wiring Repairs DTC Type Reference Powertrain Diagnostic Trouble Code (DTC) Type Definitions Scan Tool Reference Control Module References for scan tool information Circuit/System Verification 1. Engine running, observe the following control circuit parameters with a scan tool: o Fuel Press. Reg. 2 Ctrl. Ckt. Open Test Status o Fuel Press. Reg. 2 Ctrl. Ckt. Short Gnd Test Status o Fuel Press. Reg. 2 Ctrl. Ckt. Short Volt Test Status o Fuel Press. Reg. 2 High Ctrl. Ckt. Short Gnd Test Status o Fuel Press. Reg. 2 High Ctrl. Ckt. Volts Test Status Each parameter should display OK or Not Run. 2. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data. Circuit/System Testing 1. Ignition OFF, disconnect the harness connector at the Q45B fuel pressure regulator 2. 2. Connect a test lamp between the high control circuit terminal 1 and ground. Verify the test lamp does not illuminate. o If the test lamp illuminates, test the high control circuit for a short to B+. If the circuit tests normal, replace the K20 engine control module . 3. Ignition ON, verify a test lamp illuminates between the high control circuit terminal 1 and ground. o If the test lamp does not illuminate, test the high control circuit for an open, high resistance or short to ground. If the circuit tests normal, replace the K20 engine control module. 4. Ignition ON, verify that a test lamp does not illuminate between the low control circuit terminal 2 and ground. o If the test lamp illuminates , test the low control circuit for a short to voltage. If the circuit tests normal, replace the K20 engine control module. 5. Ignition ON, verify a test lamp illuminates between the low control circuit terminal 2 and B+. o If the test lamp does not illuminate, test the low control circuit for an open or high resistance. If the circuit tests normal, replace the K20 engine control module. 6. Ignition OFF, Observe that the test lamp flashes 2 times and remains OFF until the ECM is powered down. o If the test lamp does not flash 2 times and turn OFF, test the low control circuit for a short to ground. If the circuit tests normal, replace the K20 engine control module. 7. If all circuits tests normal, replace the Q45B fuel pressure regulator 2. Repair Instructions Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Fuel Pressure Relief Valve Replacement Perform the scan tool Diesel Particulate Filter (DPF) Regeneration Enable procedure if the scan tool DPF Soot Mass is less than 40 g. If the scan tool DPF Soot Mass is 40 g or greater, perform the Diesel Particulate Filter (DPF) Service Regeneration procedure. Control Module References for ECM replacement, programming, and setup. © 2015 General Motors. All rights reserved.
