P0125

1NZ-FXE 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 in the engine coolant temperature sensor and changes its resistance value according to the engine coolant temperature.
The structure of the sensor and connection to the ECM are the same as those of the intake air temperature sensor.





HINT: ECT represents engine coolant temperature, and IAT represents intake air temperature.

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 engine coolant temperature. The ECM applies 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 engine coolant temperature was 0°C (32°F) at engine start. After driving 5 minutes, the ECT sensor still indicates that the engine is not warm enough to begin the air-fuel ratio feedback control. The ECM interprets this as a fault in the sensor or cooling system and will set a DTC.

MONITOR STRATEGY





TYPICAL ENABLING CONDITIONS

ALL:





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, engine coolant temperature sensor circuit may be open or shorted. Perform troubleshooting on DTC P0115, P0117 or P0118 first.
- Read freeze frame data using 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 Freeze Frame Data.

PROCEDURE

1. CHECK OTHER DTC OUTPUT (IN ADDITION TO DTC P0125)
(a) Connect Techstream to the DLC3.
(b) Turn the power switch ON (IG).
(c) Turn Techstream ON.
(d) Enter the following menus: Powertrain / Engine and ECT / Trouble Code.
(e) Read the DTCs using Techstream.
Result:





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

B -- GO TO DTC CHART
A -- Continue to next step.

2. INSPECT THERMOSTAT
(a) Check the valve opening temperature of the thermostat.
OK:
Thermostat valve begins to open at temperature of 80 to 84°C (176 to 183°F)
HINT: Also check that the valve is completely closed at a temperature lower than specified above.

NG -- REPLACE THERMOSTAT
OK -- REPLACE ENGINE COOLANT TEMPERATURE SENSOR