P0125

4GR-FSE 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, of which the resistance value varies according to the ECT.
The structure of the sensor and its connection to the ECM are the same as those of the Intake Air Temperature (IAT) sensor.






MONITOR DESCRIPTION

The resistance of the ECT varies in proportion to the actual ECT. The ECT supplies a constant voltage to the sensor and monitors the signal output voltage of the sensor. The signal voltage output varies according to the changing resistance of the sensor. After the engine is started, the ECT is monitored through this signal. If the ECT sensor indicates that the engine is not yet warm enough for closed-loop fuel control, despite a specified period of time having elapsed since the engine was started, the ECM interprets this as a malfunction in the sensor or cooling system and sets the 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 closed-loop fuel (air-fuel ratio feedback) control. The ECM interprets this as a malfunction in the sensor or cooling system and sets the DTC.

MONITOR STRATEGY





TYPICAL ENABLING CONDITIONS





TYPICAL MALFUNCTION THRESHOLDS





WIRING DIAGRAM





INSPECTION PROCEDURE
HINT:
- If any of DTCs P0115, P0116, P0117 or P0118 are set simultaneously with DTC P0125, the Engine Coolant Temperature (ECT) sensor may have an open or a short circuit. Troubleshoot those DTCs 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 ANY OTHER DTCS OUTPUT (IN ADDITION TO DTC P0125)
(a) Connect Techstream to the DLC3.
(b) Turn the engine switch on (IG).
(c) Turn the tester on.
(d) Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.
(e) Read DTCs.
Result:





HINT:
If any DTCs other than P0125 are output, troubleshoot those DTCs first.

B -- GO TO DTC CHART
A -- Continue to next step.
2. INSPECT THERMOSTAT
(a) Remove the thermostat Removal.
(b) Check the valve opening temperature of the thermostat.
Standard:
80 to 84°C (176 to 183°F)
HINT:
In addition to the above check, confirm that the valve is completely closed when the temperature is below the standard.
(c) Reinstall the thermostat Installation.
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 any modifications.
NG -- REPAIR OR REPLACE COOLING SYSTEM
OK -- REPLACE ENGINE COOLANT TEMPERATURE SENSOR