Fuel Injection System

1-2-3 ENGINE COOLANT TEMPERATURE SENSOR SIGNAL

Condition(s) for DTC
^ The MFI module is dependent on the Engine Coolant Temperature (ECT) signal for computing the injection period, for example when starting from cold. If the module receives a signal equivalent to a temperature lower than -87°C (-125°F) (high signal) or higher than 175°C (350°F) (low signal), it will interpret the signal as a fault and the DTC will be recorded.

Substitute value
^ The MFI module assumes a substitute value equivalent to a temperature of 80°C (175°F).
^ The ICM starts the engine cooling fan at half speed.
^ The MFI module transmit's a temperature signal equivalent to a value of 150°C (300°F) to the ICM.

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

Fault symptom(s)
^ Engine is difficult to start or refuses to start in certain temperature ranges.
^ Driving problems during warm-up phase.
^ Post-running of engine cooling fan.

TESTING PROCEDURE





Other DTCs
^ Read other DTCs.

If DI DTCs 4-1-1 and/or MFI 4-1-1 are recorded:
- Check common ground terminal (MFI A14) for ECT sensor and Throttle Position Potentiometer at MFI module.
If DI DTCs 4-1-1 and/or MFI 4-1-1 are not recorded:
- Check Status Message





Checking 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! Engine cooling fan runs at half speed in event of permanent fault.





PERMANENT FAULT, SIGNAL TOO HIGH

Checking ground lead

NOTE: Switch OFF ignition and wait until engine cooling fan has stopped.

^ Disconnect fan.
^ Disconnect ECT sensor connector.
^ Connect ohmmeter between ECT sensor connector terminal 1 (MFI module side) and ground.

Instrument should indicate approx. 0 Ohms.

If reading Is correct:
- Check signal lead.
If reading is incorrect:
- Check lead between ECT sensor connector terminal 1 and MFI module A14 for open-circuit.





Checking ECT sensor signal lead
^ Switch ON ignition.
^ Disconnect ECT sensor.
^ Connect voltmeter across sensor connector terminals 1 and 2 (on MFl module side).

Instrument should indicate approx. 5 Volts.

If reading Is correct:
- Check sensor resistance.
If instrument indicates over 5 Volts:
- Check lead between sensor connector terminal 2 and MFI module A15 for short-circuit to supply.
When fault has been corrected:
- Check sensor signal.
If Instrument Indicates approx. 0 Volts:
- Check lead between sensor connector terminal 2 and MFI module A15 for open-circuit.





Checking ECT sensor resistance
^ Switch OFF ignition.
^ Disconnect sensor.
^ Connect ohmmeter between sensor connector terminals 1 and 2 (on sensor side).





Instrument should indicate approx. 2200 Ohms at +25°C (77 °F) (see chart).

If reading is correct:
- DTC is due to faulty connection in sensor connector. Check connector for contact resistance and oxidation.
If reading is incorrect:
- Try with new sensor.





Checking ECT sensor signal
^ Sensor may fail if signal lead is short-circuited to supply voltage. Check sensor signal as described below.
^ Reconnect sensor connector (if disconnected).
^ Erase DTC.
^ START engine and allow to idle.

If sensor is faulty:
- DTC will be recorded within 20 seconds.
If DTC 1-2-3 is recorded:
- Try with new sensor.

PERMANENT FAULT, SIGNAL TOO LOW





Checking signal lead
^ Disconnect engine cooling fan.
^ START engine and allow to idle.
^ Display DTC parameter list.
^ Read ECT sensor signal value.
^ Disconnect sensor connector and check if signal increases.

If value increases to approx. 5 Volts:
- Try with new sensor.
If value does not increase:
- Check lead between sensor connector terminal 2 and MFI module A15 for short-circuit to ground.