DTC EFI-123

1-2-3 ENGINE COOLANT TEMPERATURE SENSOR SIGNAL





Trouble Code Conditions
- Diagnostic trouble code (DTC) EFI-123 is stored if the engine control module (ECM) receives a signal from the engine coolant temperature (ECT) sensor corresponding to a temperature lower than -44°C (-47°F) (signal high) or higher than +148°C (+298°F) (signal low).
- As soon as the engine is started the temperature is calculated theoretically. The calculated engine coolant temperature, which is dependent on outside temperature (from the outside temperature sensor), is compared with the signal from the engine coolant temperature sensor.
- Diagnostic trouble code EFI-123 is stored if the set time (depending on starting temperature) between the engine being started and it reaching +28°C (+82.4°F) is exceeded.

Substitute value(s)
- While the car is being driven the calculated engine coolant temperature is adopted.
- When the car is restarted a substitute value of 30°C (+86°F) is adopted and when the engine has started the engine coolant temperature is calculated theoretically.
- With ignition on the engine coolant fan operates at low-speed.
- When the engine is running the engine coolant fan operates at high-speed.
- When the engine is switched off the engine coolant fan runs on for 3 minutes.
- Idle air trim adaptation disabled.
- Long-term fuel trim disabled.
- Leakage diagnostic is disabled.


Possible source(s)
Signal too high:
- Short-circuit to supply voltage in signal cable.
- Open-circuit in signal cable or ground lead.
- Contact resistance in terminals.
- Defective engine coolant temperature sensor.

Signal too low:
- Short-circuit to ground in signal cable.
- Defective engine coolant temperature sensor.

Faulty signal:
- Defective engine coolant temperature sensor.
- Defective coolant thermostat.
- Contact resistance in terminals.
- Short-circuit between signal cable and another cable.

Fault symptom(s)
- Difficult to start in certain temperature ranges.
- With ignition ON the engine coolant fan operates at low-speed.
- When the engine is running the engine coolant fan operates at high-speed.
- When the engine is switched off, the engine coolant fan runs on for 3 minutes.





Other DTCs and Status Messages
- Read off other diagnostic trouble codes.
- Are diagnostic trouble codes EFI-314 and EFI-411 stored?

Yes:
^ Proceed to: Checking Components section below.

No:
^ Proceed to: Status Messages section below.

Checking Components
- Check common engine coolant temperature sensor, camshaft position (CMP) sensor and throttle position (TP) sensor terminal # A18 on the engine control module for contact resistance, oxidation and permanent fault, and for open-circuits.
- Proceed to: Verification section below.

Verification
After carrying out the repair, check that the fault has been remedied as follows:

- Ignition OFF.
- Reconnect connectors, reinstall components etc.
- Connect engine cooling fan.
- Connect multimeter 999 6525 with temperature box 999 5281 and temperature sensor 999 5282.
- Carefully remove the expansion tank cover.

Warning: Danger - coolant is hot.

- Clamp the hose between the radiator and thermostat housing using a hose clip and disconnect the hose from the thermostat housing.
- Insert sensor in thermostat housing and reinstall hose.
- Remove hose clip.
- Start engine and run to normal operating temperature. The engine should be hot enough for the thermostat to open.
- Go into scrolling values.
- Read off engine coolant temperature.
- Is the engine coolant temperature value within its permifled range.

If reading is OK:
^ Fault corrected.

If reading is incorrect:
^ Fault not found.