Hot Coolant Light

TEST CONDITION(S)
1. Engine is running.
2. Coolant temperature not failed.
3. No data line codes set.

FAILURE CONDITION(S)
1. Engine coolant temperature greater than 126 degrees centigrade.
OR
1. Engine Overheat condition already present.
2. Engine coolant temperature greater than 120 degrees centigrade.

ACTION TAKEN
1. Turn on Hot telltale on IPC.

DESCRIPTION
The ECM provides and internally monitors voltage to the coolant temperature sensor circuit through pin 2B9. As the coolant temperature goes from cold to hot, the sensors resistance goes from high to low, and the Voltage level that the ECM detects at pin 2B9 goes from high to low. Every 1 second, the BCM checks the ECM for the coolant temperature. If the calculated coolant temperature reaches 126 degrees centigrade (i.e. the voltage at pin 2B9 of the ECM drops low enough), and all other failure conditions are met, the BCM will cause the Hot Coolant light on the IPC to come on. Refer to ENGINE OVERHEAT DIAGNOSIS in Cooling Systems. Cooling System

DIAGNOSIS
Condition
Erroneous Message - Short to ground on CKT 410 or shorted switch
NO Message - Open in CKT 410, CKT 4S2, or open in switch