Coolant Temperature Sensor/Switch (For Computer): Description and Operation

Coolant Temperature Sensor
The coolant temperature sensor located in the coolant thermostat housing controls the warm-up enrichment delivered by the ECU. In addition to the enrichment generated during warm-up, further enrichment is required during engine cranking. The cranking signal to the ECU is via a connection from the starter relay.

When the engine fires and the starter is released, the start enrichment decays slowly to the normal fuelling level temperature as determined by the engine coolant.

This over fuelling is known as the "after start enrichment". The "normal" fuelling level is determined by the engine coolant temperature, such that the fuelling level increases as the temperature decreases.