Cooling System Related Diagnostics

WARNING: This page is about a different car, the 2005 Jeep Grand Cherokee. However, it is still accessible from the selected car via links, so may be relevant.

The powertrain control module (PCM) has been programmed to monitor certain cooling system components:

If the engine has remained cool for too long a period, such as with a stuck open thermostat, a Diagnostic Trouble Code (DTC) can be set.
If an open or shorted condition has developed in the relay circuit controlling the electric radiator fan or fan control solenoid circuit controlling the hydraulic fan, a Diagnostic Trouble Code (DTC) can be set.

If the problem is sensed in a monitored circuit often enough to indicated an actual problem, a DTC is stored. The DTC will be stored in the PCM memory for eventual display to the service technician. (Refer to EMISSIONS CONTROL - DESCRIPTION) .