DTC 1-2-3 Engine Coolant Temperature Sensor Signal

1-2-3 ENGINE COOLANT TEMPERATURE SENSOR SIGNAL

Preconditions for DTCs
^ If the ECM receives a signal from the Engine Coolant Temperature (ECT) sensor which indicates a temperature lower than -45°C (-49°F) (high signal) or higher than +15O°C (3OO°F) (low signal) this is interpreted as a fault and DTC 1-2-3 is set.
^ A specific period should pass from engine start until the engine reaches a temperature of +28°C (82°F), depending on starting temperature. If this temperature is exceeded, the control module interprets this as a fault (faulty signal) and DTC 1-2-3 is set.

Substitute values
^ At start-up, a substitute value of +2O°C (68°F) is assumed, rising after start-up to +83°C (181°F).
^ The engine cooling fan starts running at half speed.
^ The AC valve's idle air trim is inhibited.
^ Long term fuel trim inhibited.

Fault sources
^ Signal too high:
- Signal lead short circuited to voltage.
- Break in signal or ground lead.
- Contact resistance in connectors.
- Defective ECT sensor.

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

^ Incorrect signal:
- Defective ECT sensor.
- Defective coolant thermostat.
- Contact resistance in connectors.
- Signal lead short circuited to another lead.

Fault symptoms
^ Difficulty in starting in certain temperature ranges.
^ Engine fan runs for 3 minutes after engine shutdown.