P0125

2UZ-FE ENGINE CONTROL SYSTEM: SFI SYSTEM: P0125: Insufficient Coolant Temperature for Closed Loop Fuel Control

DTC P0125 - Insufficient Coolant Temperature for Closed Loop Fuel Control

DESCRIPTION

- A thermistor is built into the Engine Coolant Temperature (ECT) sensor and changes the resistance value according to the engine coolant temperature.
The structure of the sensor and connection to the ECM is the same as the Intake Air Temperature (IAT) sensor.
HINT: If the ECM detects the DTC P0115, P0117 or P0118, it operates the fail-safe function in which the ECT is assumed to be 80°C (176°F).






MONITOR DESCRIPTION

The Engine Coolant Temperature (ECT) sensor is used to monitor the temperature of the engine coolant. The resistance of the sensor varies with the actual coolant temperature. The ECM applies a voltage to the sensor and the varying resistance of the sensor causes the signal voltage to vary. The ECM monitors the ECT signal voltage after engine start-up. If the sensor still reports that the engine is not warmed up enough for closed-loop fuel control after sufficient time has passed, the ECM interprets this as a fault in the sensor or cooling system and sets a DTC.
Example:
The ECT is 0°C (32°F) at engine start. After 78 seconds running time, the ECT sensor still indicates that the engine is not warm enough to begin air-fuel ratio feedback control of the air-fuel ratio. The ECM interprets this as a fault in the sensor or cooling system and will set a DTC.

MONITOR STRATEGY





TYPICAL ENABLING CONDITIONS





Case 1





Case 2





Case 3





TYPICAL MALFUNCTION THRESHOLDS





WIRING DIAGRAM





INSPECTION PROCEDURE
HINT:
- If DTCs P0115, P0116, P0117, P0118 and P0125 are output simultaneously, an ECT sensor circuit may be open or shorted. Perform the troubleshooting of DTC P0115, P0117 or P0118 first.
- Read freeze frame data using the Techstream. The ECM records vehicle and driving condition information as freeze frame data the moment a DTC is stored. When troubleshooting, freeze frame data can be helpful in determining whether the vehicle was running or stopped, whether the engine was warmed up or not, whether the air/fuel ratio was lean or rich, as well as other data recorded at the time of a malfunction.

PROCEDURE

1. CHECK ANY OTHER DTCS OUTPUT (IN ADDITION TO DTC P0125)
(a) Connect the Techstream to the DLC3.
(b) Turn the ignition switch ON and turn the tester ON.
(c) Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.
(d) Read the DTCs.
Result:





HINT: If any other codes besides P0125 are output, perform the troubleshooting for those codes first.

B -- GO TO RELEVANT DTC CHART
A -- Continue to next step.
2. INSPECT THERMOSTAT
(a) Remove the thermostat Removal.
(b) Check the valve opening temperature of the thermostat Testing and Inspection.
OK:
Valve opening temperature is 80 to 84°C (176 to 183°F)
HINT: Also check that the valve is completely closed below the opening temperature shown above.
(c) Reinstall the thermostat Installation.
NG -- REPLACE THERMOSTAT
OK -- Continue to next step.
3. CHECK COOLING SYSTEM
(a) Check that there is a defect in the cooling system which causes overcool, such as abnormal radiator fan operation, modified cooling system and so on.
NG -- REPAIR OR REPLACE COOLING SYSTEM
OK -- REPLACE ENGINE COOLANT TEMPERATURE SENSOR