Download DTC P0125 Insufficient Coolant Temperature for

DI–195
DIAGNOSTICS
–
ENGINE (5VZ–FE)
DI8YY–02
DTC
P0125
Insufficient Coolant Temperature for Closed
Loop Fuel Control
CIRCUIT DESCRIPTION
To obtain a high purification rate of the CO, HC and NOx components of the exhaust gas, a three–way catalytic converter is used. For the most efficient use of the three–way catalytic converter, the air–fuel ratio must
be precisely controlled so that it is always close to the stoichiometric air–fuel ratio.
The A/F sensor has a characteristic of providing an output voltage* approximately proportional to the existing
air–fuel ratio. The A/F sensor output voltage* is used to provide feedback for the ECM to control the air–fuel
ratio.
By the A/F sensor output, the ECM can determine the deviation amount from the stoichiometric air–fuel ratio
and control the proper injection time immediately. If the A/F sensor is malfunctioning, the ECM is unable to
perform the accurate air–fuel ratio control.
The A/F sensor is equipped with a heater which heats the zirconia element. The heater is controlled by the
ECM. When the intake air volume is low (the temperature of the exhaust gas is low), current flows to the
heater to heat the sensor for the accurate oxygen concentration detection.
*: The voltage value changes at the inside of the ECM only.
Platinum
Electrode
Solid Electrolyte
(Zirconia Element)
Platinum
Electrode
Heater
ECM Monitored
A/F Sensor Voltage
Atmosphere
(V)
4.0
3.8
3.6
3.4
3.2
3.0
2.8
2.6
2.4
Coating (Ceramic)
12
13 14
15 16 17 18 19
Air–Fuel Ratio
Cover
Exhaust Gas
A00477
DTC No.
P0125
DTC Detection Condition
After engine is warmed up, A/F sensor output* does not
change when conditions (a), (b) and (c) continue for at least
1.5 min.:
*: Output value changes at inside of ECM only
(a) Engine speed: 1,500 rpm or more
(b) Vehicle speed: 40 – 100 km/h (25 – 62 mph)
(c) Throttle valve does not fully closed
(d) After starting engine 140 sec.
Trouble Area
PCV hose connection
PCV hose
Open or short in A/F sensor (bank 1 sensor 1) circuit
A/F sensor (bank 1 sensor 1)
Air induction system
Fuel pressure
Injector
Gas leak on exhaust system
ECM
HINT:
After confirming DTC P0125, use the hand−held tester or OBD II scan tool to confirm output voltage
of the heated oxygen sensor (bank 1 sensor 1) from the CURRENT DATA.
The ECM controls the voltage of the AF1+ and AF1– terminals of the ECM to the fixed voltage. Therefore it is impossible to confirm the A/F sensor output voltage without hand–held tester or OBD II scan
tool.
2002 TOYOTA TACOMA (RM921U)
DI–196
DIAGNOSTICS
–
ENGINE (5VZ–FE)
OBD II scan tool (excluding hand–held tester) displays the one fifth of the A/F sensor output voltage
which is displayed on the hand–held tester.
WIRING DIAGRAM
13
W–R
3E
W–R
IK2
3
J/B No. 3
1
W–R
From
IF1
Terminal 3 of
EFI Relay
(See page DI–285)
BR
3
R
2
IK2
BR
1
14
E8
ECM
AF1+
A23
A/F Sensor
(Bank 1 Sensor 1)
21
HTAF1
W
4
E8
P
26
AF1– E03
E8
R
27
OX2B
E8
W–R
5
EF
V
W–R
3E 1
7
W–R
2
22
IK2
3 H9
Heated Oxygen Sensor
(Bank 1 Sensor 2)
12
R–W
4
IK2
29
R–W
E8
HT2B
E03
A18634
INSPECTION PROCEDURE
HINT:
If the vehicle runs out of fuel, the air–fuel ratio is LEAN and DTC P0125 will be recorded. The MIL then
comes on.
Read freeze frame data using hand–held tester or OBD II scan tool, as freeze frame data records the
engine conditions when a malfunction is detected. When troubleshooting, it is useful for determining
whether the vehicle was running or stopped, the engine was warmed up or not, the air–fuel ratio was
lean or rich, etc. at the time of the malfunction.
1
Are there any other codes (besides DTC P0125) being output?
YES
Go to relevant DTC chart (See page DI–167).
NO
2
Check connection of PCV hose.
NG
OK
2002 TOYOTA TACOMA (RM921U)
Repair or replace PCV hose.
DI–197
DIAGNOSTICS
3
–
ENGINE (5VZ–FE)
Connect hand–held tester or OBD II scan tool, and read value for output voltage
of A/F sensor (bank 1 sensor 1).
PREPARATION:
(a) Connect the hand–held tester or OBD II scan tool to the DLC3.
(b) Warm up the A/F sensor with the engine speed at 2,500 rpm for approx. 90 seconds.
CHECK:
Read the voltage value of the A/F sensor on the screen of the hand–held tester or OBD II scan tool when
performing all the following conditions.
HINT:
The voltage of the AF1+ terminal of the ECM is fixed at 3.3 V and the AF1– terminal is fixed at 3.0 V. Therefore
it is impossible to check the A/F sensor output voltage at the terminals (AF1+/AF1–) of the ECM.
OK:
Condition
Engine idling
Engine racing
Driving at engine speed 1,500 rpm or more and vehicle
speed 40 km/h (25 mph) or move, and operate throttle valve
open and close
A/F Sensor Voltage value
N
Nott remains
i att 3.3.
3 3 V (0.660
(0 660 V*)
Not remains at 3
3.8
8 V (0.76
(0 76 V*) or more
Not remains at 2.8 V (0.56 V*) or less
*: When using the OBD II scan tool (excluding hand–held tester)
HINT:
Although there is a case that the output voltage of the A/F sensor is below 2.8 V (0.56 V*) during fuel
enrichment, it is normal.
Although there is a case that the output voltage of the A/F sensor is above 3.8 V (0.76 V*) during fuel
cut, it is normal.
If the output voltage of the A/F sensor remains at 3.30 V (0.660 V*) even after performing all the above
conditions, the A/F sensor circuit may be open.
If the output voltage of the A/F sensor remains at 3.8 V (0.76 V*) or more, or 2.8 V (0.56 V*) or less
even after performing all the above conditions, A/F sensor circuit may be short.
*: When using the OBD II scan tool (excluding hand–held tester).
OK
Go to step 9.
NG
4
Check for open and short in harness and connector between ECM and A/F sensor (bank 1 sensor 1) (See page IN–28).
NG
Repair or replace harness or connector.
OK
5
Check resistance of A/F sensor heater (bank 1 sensor 1) (See page SF–55).
2002 TOYOTA TACOMA (RM921U)
DI–198
DIAGNOSTICS
–
NG
ENGINE (5VZ–FE)
Replace A/F sensor.
OK
6
Check air induction system (See page SF–1).
NG
Repair or replace.
OK
7
Check fuel pressure (See page SF–5).
NG
Check and repair fuel pump, pressure regulator,
fuel pipe line and filter.
OK
8
Check injector injection (See page SF–19).
NG
Replace injector.
NG
Repair or replace.
OK
9
Check gas on exhaust system.
OK
Replace A/F sensor (bank 1 sensor 1).
2002 TOYOTA TACOMA (RM921U)
DI–199
DIAGNOSTICS
10
–
ENGINE (5VZ–FE)
Perform confirmation driving pattern (See page DI–260).
Go
11
Is there DTC P0125 being output again?
YES
Check and replace ECM (See page IN–28).
NO
12
Did vehicle run out of fuel in past?
NO
YES
DTC P0125 is caused by shortage of fuel.
2002 TOYOTA TACOMA (RM921U)
Check for intermittent problems (See page
DI–157).