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

WARNING: This page is about a different car, the 2016 Lincoln MKS. However, it is still accessible from the selected car via links, so may be relevant.

Diagnostic Overview

Normal Operation and Fault Conditions

Warm coolant flows from the engine through the heater core and back to the engine. Proper coolant temperatures are critical for good heater performance.

Possible Sources

Missing or broken engine coolant hose check valve or incorrect orientation of check valve (3.5L only)
Plugged or partially plugged heater core
Low engine coolant level
Temperature blend door actuator(s)
Temperature blend door(s) binding or stuck