Coolant Heater Inoperative

Coolant Heater Inoperative (Diesel)

Diagnostic Instructions
^ Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
^ Review Strategy Based Diagnosis for an overview of the diagnostic approach.
^ Diagnostic Procedure Instructions 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
^ Connector Repairs
^ Testing for Intermittent Conditions and Poor Connections
^ Wiring Repairs

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 after completing the diagnostic procedure. Verification Tests
^ Coolant Heater Replacement (4.8L, 5.3L (except RPO L33), 6.0L) Coolant Heater Replacement (5.3L (w/RPO L33)) Coolant Heater Replacement (6.6L) Coolant Heater Replacement (8.1L) Coolant Heater Replacement (4.3L)
^ Coolant Heater Cord Replacement (4.8L, 5.3L (except RPO L33), 6.0L) Coolant Heater Cord Replacement (5.3L (w/RPO L33))