Coolant Heater Inoperative

Coolant Heater Inoperative (Diesel)

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) provides an overview of each diagnostic category.

Circuit/System Description

The optional coolant heater operates using 110 volt AC external power and is designed to warm the coolant in the engine block area for improved starting in very cold weather. There are two heater cords available. One has an internal thermal switch in the power cord that prevents operation above -18°C (0°F) and the other operates at all temperatures. A weather shield on the cord is provided to protect the plug when not in use.

Reference Information
Electrical Information Reference

* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)

Circuit/System Testing

Important: The heater cord with a thermal switch will read open if the ambient temperature is above -18°C (0°F). A heater cord without a thermal switch can be tested for an open at any temperature.

1. Test the engine coolant heater for an open or short to ground.

• If open or shorted, replace the heater.

2. If the heater tests normal, replace the coolant heater power cord.

Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

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* Coolant Heater Cord Replacement (4.3 L Engine) (Coolant Heater Cord Replacement)Coolant Heater Cord Replacement (4.8L, 5.3L And 6.0L Engine) (Coolant Heater Cord Replacement)Coolant Heater Cord Replacement (6.6 L Engine) (Coolant Heater Cord Replacement)