P0125

COOLANT TEMPERATURE, SLOW INCREASE





Symptom Of Fault.
The CHECK ENGINE lamp (MIL) is on.

Conditions.
Engine running
Vehicle speed > 12 mph (> 20 km/h)
The coolant temperature does not rise by 20°C (36°F) from starting temperature or reach 40°C (104°F) within 6 minutes and 40 seconds.

Diagnostic Help.
The diagnostic trouble code may be generated as a result of:
^ connection of a non-approved external parking heater
^ ice formation in the cooling system
^ a fault in the coolant temperature sensor or its circuit
^ a defective thermostat.





Diagnostic Procedure.
1. Check the anti-freeze
At ambient temperatures below 0°C (32°F), check the freezing point of the coolant.

Is the freezing point OK?
YES:
^ Continue with point 2.
NO:
^ Rectify the fault and proceed to point 4.

2. Check the thermostat
The engine should be cold enough to allow a hand to be placed on the cylinder head without discomfort.
- Connect an ISAT scan tool and contact the EDU.
- Select "READ VALUES".
- Select "COOLANT TEMPERATURE".
- Start the engine and warm it up at idling speed. Feel the upper radiator hose, near the thermostat, to check that it quickly becomes hot when the coolant reaches a temperature of about 89°C (192°F) and the thermostat opens.

Following this, the coolant temperature should remain fairly constant at about 89°C (192°F) for a minute or so.

Is the thermostat OK?
YES:
^ Continue with point 3.
NO:
^ Change the thermostat and proceed to point 4.





3. Check the coolant temperature sensor
- Engine running at idling speed.
- Connect an ISAT scan tool.
- Contact the Trionic system.
- Select "READ FUNCTIONS".
- Select "COOLANT TEMPERATURE".
- Note the temperature.
- Contact the EDU.
- Select "READ VALUES".
- Select "COOLANT TEMPERATURE".
- Note the temperature.
The difference between the two temperature readings should not be more than 5°C (9°F).

Are the readings OK?
YES:
^ Continue with point 4.
NO:
^ See fault diagnosis for diagnostic trouble codes P0115, P0117 and P0118.





4. Final check:
- Clear the diagnostic trouble code.
- Implementation of driving cycle: Warm up the engine at idling speed until the radiator fan cuts in.
- Evaluation of driving cycle: Unplug the temperature sensor's connector from the EDU so that the radiator fan will run continuously. Check that the coolant temperature in the Trionic system drops to and stabilizes at about 89°C (192°F).

Is the function OK?
YES:
^ Proceed at "Before Replacing a Control Module". Component Tests and General Diagnostics
NO:
^ The remedial measure taken was correct.
- Clear the diagnostic trouble code for the temperature sensor in the EDU.