P0116

ENGINE COOLANT TEMPERATURE, SLOW RISE





Fault Symptom.
CHECK ENGINE lamp (MIL) on.

Conditions.
P0116
^ The coolant temperature is 10°C below the calculated engine temperature.

Diagnostic Help.
The diagnostic trouble code is generated as a result of
^ the 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.

Check The Wiring.
Intermittent faults may occur as a result of temporary short circuits and breaks in the wiring. Jiggle the wiring at several points and in different directions to ascertain whether the wiring harness, including any connectors, is causing the trouble. Observe the multimeter, ISAT scan tool or test lamp while doing this.





1. Check the freezing point

Check the freezing point of the coolant when the outside temperature is below 0°C (32°F).

Is the freezing point OK?

YES: Continue with point 2.
NO: Rectify the fault and continue with 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 FUNCTIONS".
- Select "COOLANT TEMPERATURE".
- Start the engine and warm it up at idling speed. Place a hand on the upper radiator hose near the thermostat to feel whether it quickly becomes hot when the temperature of the coolant reaches about 92°C (198°F) and the thermostat opens.

The coolant thermostat should then remain relatively constant at this temperature (about 92°C [198°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 the ISAT Scan Tool.
- Establish communication with the Motronic system.
- SELECT "READ FUNCTIONS".
- Select "COOLANT TEMPERATURE".
- Make a note of the temperature.
- Establish communication with the EDU.
- Select "READ VALUES".
- Select "COOLANT TEMPERATURE".
- Make a note of the temperature.

The two temperature readings should not differ by more than a maximum of 5°C (9°F).

Are the temperature readings OK?

YES: Continue with point 4.
NO: See the fault diagnosis procedure for diagnostic trouble codes 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 Motronic system drops to and stabilizes at about 92°C (198°F).

Result unsatisfactory?

YES: Continue as described at "Before Replacing a Control Module". Component Tests and General Diagnostics
NO: The steps taken to rectify the fault were correct. Clear the diagnostic trouble code for the temperature sensor in the EDU.