Diagnostic Chart

P0125 - Insufficient Coolant Temperature for Closed Loop Fuel Control

CIRCUIT DESCRIPTION

DTC Detection Condition:

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.

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.
- 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:

CONFIRMATION DRIVING PATTERN

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 mode.
c. Start the engine and warm it up with all the accessory switched OFF.
d. Drive the vehicle at 60 - 120 km/h (38 - 75 mph) and the engine speed at 1,600 - 3,200 rpm for 3 - 5 minutes.

HINT: If a malfunction exists, the MIL will light up during step (d).

NOTE:
- If the conditions in this test are not strictly followed, detection of the malfunction will impossible.
- Without a hand-held tester, turn the ignition switch OFF after performing steps (c) and (d), then perform steps (c) and (d) again.

Step 1 - 2:

Step 3 - 5:

Step 5(continued) - 9:

Step 10 - 12:

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.

CHECK FOR INTERMITTENT PROBLEMS

HINT:
Hand-held tester only:
By putting the vehicle's ECM in check mode, 1 trip detection logic is possible instead of 2 trip detection logic and sensitivity to detect open circuits is increased. This makes it easier to detect intermittent problems.

a. Clear the DTCs.
b. Set the check mode.
c. Perform a simulation test.
d. Check the connector and terminal.
e. Handle the connector.