The ECM controls cooling fan speed (low,medium, high) based on engine coolant temperature, vehicle speed, and A/C switch position. Fans will default to high-speed operation upon ECT or VSS failure.
ECM sets DTC P1624 if the ECM detects that the fan relay control line is open, short to ground or battery.
Item  | Detecting Condition  | Possible Cause  | 
DTC Strategy  | ● Driver stage check  | ● Contact resistance in connectors ● Open or short circuit ● Malfunctioning fan relay  | 
Enable Conditions  | ● Battery voltage > 10V  | |
Threshold Value  | ● Open or short to ground ● Short to battery  | |
Diagnostic Time  | ● 10 seconds  |