Diagnostic Chart
DTC P0125 Insufficient Coolant Temp. for Closed Loop Fuel ControlCIRCUIT DESCRIPTION
DTC Detection Condition:
To obtain a high purification rate for the CO, HC and NOx components of the exhaust gas, a three-way catalytic converter is used. But, 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 the characteristic that provides 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, ECM is unable to perform 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 temp. of the exhaust gas is low), current flows to the heater to heat the sensor for accurate oxygen concentration detection.
*: The voltage value changes at the inside of the ECM only.
HINT:
- Bank 1 refers to the bank that includes cylinder No.1.
- Bank 2 refers to the bank that includes cylinder No.2.
- Sensor 1 refers to the sensor closet to the engine body.
- If DTC P0125 is displayed, check Bank 1 Sensor 1 circuit.
- If DTC P0125 is displayed, check Bank 2 Sensor 1 circuit.
- After confirming DTC P0125, use the OBD II scan tool or TOYOTA hand-held tester to confirm the voltage output of the A/F sensor (AFS B1 S1/O2S B1 S1) from the CURRENT DATA.
- The A/F sensor's output voltage and the short-term fuel value can be read using the OBD II scan tool or TOYOTA hand-held tester.
- The ECM controls the voltage of AF1A+/AF2A+ and AF1A-/AF2A- terminals of the ECM to the fixed voltage. Therefore, it is impossible to confirm the A/F sensor output voltage without the OBD II scan tool or TOYOTA hand-held tester.
Wiring Diagram:
Step 1 - 3:
Step 3 (Continued):
Step 3 (Continued) - 8:
Step 8 (Continued) - 12:
Step 13 - 17:
Step 18 - 19:
INSPECTION PROCEDURE
HINT:
- If DTC P0125 is displayed, check Bank 1 Sensor 1 circuit.
- If DTC P0125 is displayed, check Bank 2 Sensor 1 circuit.
- Read freeze frame data using TOYOTA hand-held tester or the 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.
Confirmation Driving Pattern
a. Connect the hand-held tester to the DLC3.
b. Switch the hand-held tester from the normal mode to the check (test) mode.
c. Start the engine and let the engine idle for 60 seconds or more.
d. Drive the vehicle at 40 km/h (24 mph) or more for 40 seconds or more.
e. Let the engine idle for 10 seconds or more.
f. Preform steps (d) to (e) 9 times.
HINT: If a malfunction exists, the MIL will light up on the multi information display during step (f).
NOTE: If the conditions in this test are not strictly followed, the malfunction detection is impossible. If you do not have a hand-held tester, turn the ignition switch OFF after performing steps from (c) to (f) once, then perform steps from (c) to (f) again.
Check For Intermittent Problems
TOYOTA hand-held tester only:
By putting the vehicle's ECM in the check mode, 1 trip detection logic is possible instead of 2 trip detection logic and the sensitivity to detect open circuits is increased. This makes it easier to detect intermittent problems.
1. Clear the DTCs.
2. Set the check mode.
3. Perform a simulation test.
4. Check the connector and terminal.
5. Handle the connector.