Ignition System

1-2-3 ENGINE COOLANT TEMPERATURE SENSOR SIGNAL

Condition(s) for DTC
^ If the ICM receives a signal corresponding to a temperature below -40°C (-40°F) (high signal value) or over 145°C (293°F) (low signal value), it will interpret the condition as a fault and the DTC will be recorded.

Substitute value
^ The ICM assumes a substitute value corresponding to a temperature of to 95°C (203°F).
^ The engine cooling fan is started at half speed.
^ Post-running of the fan at half speed continues for 3 minutes.

Fault source(s)
^ Signal too high:
- Signal lead short-circuited to supply.
- Open-circuit in signal lead.
- Contact resistance in connections.

^ Signal too low:
- Signal lead short-circuited to ground.

Fault symptom(s)
^ Engine is difficult or fails to start in certain temperature ranges.

TESTING PROCEDURE





Other DTCs
^ Read other DTCs.

If MFI DTC 1-2-3 is recorded:
- Proceed to Testing By Trouble Code / Fuel Injection System / DTC 1-2-3 Engine coolant temperature (ECT) Sensor Signal.
If DI DTC 1-4-4 is recorded:
- Proceed to DTC 1-4-4 Mass Air Flow Sensor (Load signal).
If neither DTC is recorded:
- Check Status message.





Status message
^ Check current Status Message.

If Status message is: Permanent fault, signal too high:
- Proceed to PERMANENT FAULT, SIGNAL TOO HIGH Section below.
If Status message is: Permanent fault, signal too low:
- Proceed to PERMANENT FAULT, SIGNAL TOO LOW Section below.
If Status message is: Intermittent fault, signal too high:
- Proceed to INTERMITTENT FAULT, SIGNAL TOO HIGH Section below.
If Status message is: Intermittent fault, signal too low:
- Proceed to INTERMITTENT FAULT, SIGNAL TOO LOW Section below.

CAUTION: The engine cooling fan will run at half speed in the event of a permanent fault.

^ The fault counter indicates the number of starts during which the ICM has detected a fault-free signal after the DTC has been recorded.

PERMANENT FAULT, SIGNAL TOO HIGH

Checking signal lead
^ Disconnect engine cooling fan.





^ Connect test box to DI system and check ground terminals.





^ Plug ICM into test box adapter.
^ Switch ON ignition.
^ Connect voltmeter across #53 (DI B23) and #20 (DI A20) on test box.

Instrument should indicate 5 - 6 Volts.

If reading is correct:
- DTC is due to poor connection in control module connector. Check connector for contact resistance and oxidation.
- Check signal after fault has been corrected.
If instrument indicates approx. 0 Volts:
- Check lead between MFI B23 and ICM B23 for open-circuit.
If Instrument indicates battery voltage:
- Check lead between MFI B23 and ICM B23 and lead between ICM B23 and combined instrument A26 for short-circuit to supply.
- On cars with ECC, also check lead connected to ECC A23 for short-circuit to supply.





Checking signal
^ Disconnect test box.
^ Connect ICM.
^ Erase DTC.
^ START and STOP engine several times.

If DTC recurs:
- Try with new ICM.

PERMANENT FAULT, SIGNAL TOO LOW





Checking signal lead for short-circuit to ground
^ Disconnect engine cooling fan.
^ Check lead between MFI B23 and ICM B23, and lead between ICM B23 and combined instrument A26, for short-circuit to ground.
^ On cars with ECC, also check lead connected to ECC A23 for short-circuit to ground.

INTERMITTENT FAULT, SIGNAL TOO HIGH





Checking wiring and connections
^ Check MFI module and ICM connectors for loose connections, and for contact resistance and oxidation.
^ Check lead between MFI B23 and ICM B23 for intermittent open-circuit.
^ Check lead between MFI B23 and ICM B23, and lead between ICM B23 and combined instrument A26, for short-circuit to supply.
^ On cars with ECC, also check lead connected to ECC A23 for short-circuit to supply.

INTERMITTENT FAULT, SIGNAL TOO LOW





Checking wiring and connections
^ Check lead between MFI B23 and ICM B23, and lead between ICM B23 and combined instrument A26, for short-circuit to ground.
^ On cars with ECC, also check lead connected to ECC A23 for short-circuit to ground.