"Hot" Coolant Light

CTS Circuit:

DESCRIPTION:

The ECM supplies and internally monitors voltage to the coolant temperature sensor circuit through pin 3D4. As the coolant temperature goes from cold to hot, the sensor's resistance goes from high to low, and the voltage level the ECM detects at pin 3D4 goes from high to low. Every 1.0 second the BCM checks the ECM for the coolant temperature. If the calculated coolant temperature reaches 126°C (i.e. the voltage at pin 3D4 of the ECM drops low enough), and all other failure conditions have been met, the BCM will cause the "HOT" coolant light on the IPC to come "ON."

TEST CONDITIONS:

1. Engine is running.
2. Coolant temperature not failed.

FAILURE CONDITIONS:

1. Engine coolant temperature greater than 120°C.
2. Engine overheat condition already present.
OR
3. Coolant temperature is greater than 126°C.

ACTION TAKEN:

1. Illuminate "HOT" telltale on IPC.

DIAGNOSIS:

Erroneous Message - Short to ground on circuit 410 or shorted switch.

No Message - Open in circuit 410 or open in switch.