P0116

Fault Symptom.
CHECK ENGINE lamp (MIL) on.

Conditions.
P0116
^ Engine running
^ The indicated engine coolant temperature is lower than the that calculated by the control module.

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.

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.





Diagnostic Procedure.
1 Check the anti-freeze
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. 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 Integrated Central Electronics (ICE) module.
- 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 housing 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 temperature should then remain fairly constant at this temperature, about 89°C (192°F), for a minute or so.

Is the thermostat OK?

YES:
^ Continue with point 3.
NO:
^ Change the thermostat. Continue with point 4.





3 Check the coolant temperature sensor
- Connect an ISAT scan tool.
- Start the engine and run it at idling speed.
- Select "MOTRONIC 4.1".
- Select "READ FUNCTIONS".
- Select "COOLANT TEMPERATURE".
- Note the temperature.
- Select "ICE".
- Select "READ VALUES".
- Select "COOLANT TEMP".
- Note the temperature.

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

Are the 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 ICE module so that the radiator fan will run continuously.
^ Check that the coolant temperature in the Motronic system drops to and stabilizes at about 89°C (192°F).

Result unsatisfactory?

YES:
^ Continue 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 ICE module.