For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | 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 is an internal thermal switch in the power cord that prevents operation above -18°C (0°F). The coolant heater helps reduce fuel consumption when a cold engine is warming up. The unit is equipped with a detachable AC power cord. 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

• | Wiring Repairs

### Circuit/System Testing

Important: The power supply cord will read open due to an internal thermal switch if the ambient temperature is above -18°C (0°F).

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.

• | Coolant Heater Replacement

• | Coolant Heater Cord Replacement