Diagnostic Chart

DTC P0125 INSUFFICIENT COOLANT TEMPERATURE FOR CLOSED LOOP FUEL CONTROL

CIRCUIT DESCRIPTION

DTC Detecting Condition:

To obtain a high purification rate of the CO, HG 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 oxygen sensor has the characteristic that it provides output voltage* being approximately proportional to the existing air-fuel ratio. The oxygen sensor output voltage* is used to provide feedback for the ECM to control the air-fuel ratio.

By the oxygen sensor output, the ECM can determine the deviation amount from the stoichiometric air-fuel ratio and control the proper injection time immediately. If the oxygen sensor is out of order, ECM is unable to perform the accurate air-fuel ratio control.

The oxygen 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), the 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.

HINT: After confirming DTC P0125, use the hand-held tester or OBD II scan tool to confirm output voltage of the oxygen sensor from the CURRENT DATA.

Wiring Diagram:

Step 1 - 3:

Step 4 - 9:

Step 10 - 12:

INSPECTION PROCEDURE

HINT: Read freeze frame data using the hand-held tester or OBD II scan tool. Because freeze frame data records the engine conditions when the 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.

CHECK FOR INTERMITTENT PROBLEMS

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 DTC.
2. Set the check mode.
3. Perform a simulation test.
4. Check the connector and terminal.
5. Handle the connector.