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 engine through the heater core and back to the engine. Correct coolant temperatures are critical for good heater performance.

Possible Sources 

• Low engine coolant level
• Heater hoses kinked or restricted
• Air trapped in the coolant system
• Plugged or partially plugged heater core
• Temperature door binding or stuck
• Temperature door actuator

Visual Inspection and Diagnostic Pre-checks 

• Inspect for low engine coolant level.