Diagnostic Aids
WARNING: This page is about a different car, the 2002 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.
To locate an intermittent problem, use scan tool to monitor DTC P0050 LAST TEST just after the engine is started. The ECM will pulse the heater on and off from anywhere between 0 and 30 seconds, then the ECM will turn it off briefly every 10 seconds. Wiggling wires while watching for a change from PASSED to FAILED during the Off command may locate the area where an open in the wiring may exist.
Heater element resistance should be 7.0-20.2 ohms.