For 1990-2009 cars

### Circuit Description

The coolant temperature gage is directly controlled by the PCM using a pulse width modulated (PWM) signal, based on information from the engine coolant temperature (ECT) sensor. The PCM uses the inputs from the ECT to control fuel, the A/C cooling fan, and the low coolant/hot lamp. The ECT is the only coolant temperature sensing device on both SOHC and DOHC engines.

### Conditions for Setting the DTC

Important: The coolant gage circuit is continuously checked when the ignition is ON.

DTC P1691 will set if there is an open, short to ground, or short to voltage in the coolant gage circuit.

### Diagnostic Aids

If the scan tool Malf history indicates an open/short to power or ground, refer to the coolant circuit gage diagnosis.

A scan tool may be used to command the coolant gage. Diagnosis of coolant gage accuracy can be found in the Audio System and I/P Cluster sections.