P0125

3UZ-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).





HINT: Confirm the ECT using the Techstream. Enter the following menus: Powertrain / Engine and ECT / Data List / Coolant Temp.





MONITOR DESCRIPTION

The 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, after sufficient time has passed, the sensor still reports that the engine is not warm enough for closed loop fuel control, 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 5 minutes 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.
This monitor runs when the ECT at engine start was -6.6°C (20°F) and the engine has run 5 minutes.

MONITOR STRATEGY





TYPICAL ENABLING CONDITIONS

All





Case 1





Case 2





Case 3





TYPICAL MALFUNCTION THRESHOLDS





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. Freeze frame data records the engine conditions when a malfunction is detected. When troubleshooting, freeze frame data can help determine if the vehicle was running or stopped, if the engine was warmed up or not, if the air-fuel ratio was lean or rich, and other data from the time the malfunction occurred.

PROCEDURE

1. CHECK OTHER DTC OUTPUT (IN ADDITION TO DTC P0125)
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) Check the valve opening temperature of the thermostat.
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.

NG -- REPLACE THERMOSTAT
OK -- Continue to next step.
3. CHECK COOLING SYSTEM
(a) Check for defects in the cooling system that might cause the system to be too cold, such as abnormal radiator fan operation or a modified cooling system.
NG -- REPAIR OR REPLACE COOLING SYSTEM
OK -- REPLACE ENGINE COOLANT TEMPERATURE SENSOR