Pinpoint Test F : Insufficient, Erratic Or No Heat: Notes

Normal Operation and Fault Conditions 

When the engine is at operating temperature hot coolant flows from the coolant pump through the heater core and back to the coolant pump. Correct coolant temperatures are critical for good heater performance.

Possible Sources 

• Wiring, terminals or connectors
• Temperature door actuator(s)
• Air trapped in the coolant system
• Heater core

Visual Inspection and Diagnostic Pre-checks 

• Inspect for low engine coolant level.