Poor Heater Performance, Suspect Thermostat In Open Position

1. Does gauge read low?
^ If YES, replace thermostat. If NO, inspect the auxiliary heater vacuum water valve. The valve should be open except when the climate controls are OFF or in the MAX A/C mode.

2. Is the coolant level low?
^ Fill cooling system and inspect for leaks. Repair as necessary.

3. Check On-Board Diagnostics. Is code 17 set in memory?
^ If YES, replace thermostat. If NO, inspect the auxiliary heater vacuum water valve. The valve should be open except when the climate controls are OFF or in the MAX A/C mode.