Cylinder 1 Glow Plug Control Circuit High
The P066B code indicates that the powertrain control module (PCM) has detected a high voltage condition in the glow plug control circuit for cylinder 1. This circuit controls the glow plug used to heat the combustion chamber for cold starts in diesel engines. A high voltage reading suggests a short to power, a faulty glow plug, or a problem with the glow plug control module.
01. Most Common Causes
- Short to voltage in the glow plug circuit
- Faulty glow plug (cylinder 1)
- Failed glow plug control module
- Corroded or damaged wiring/connectors
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Hard starting, especially in cold weather
- Rough idle or misfire on cylinder 1
- Excessive smoke from exhaust during startup
03. Step-by-Step Diagnosis
Step 1: Use a scan tool to confirm the code and check for additional codes.
Step 2: Visually inspect the glow plug wiring and connector for cylinder 1 for damage or corrosion.
Step 3: Measure resistance of glow plug cylinder 1; compare to spec (typically 0.5-2 ohms).
Step 4: Check for voltage at the glow plug connector with key on; should be battery voltage. If high, trace short to power.
Step 5: Test the glow plug control module output to cylinder 1; replace if faulty.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive with this code, as it can cause hard starting, poor engine performance, and potential damage to the glow plug system or PCM.
How much does it cost to fix?▼
The cost to fix P066B typically ranges from $50 to $150 for parts and labor, depending on whether a glow plug or wiring repair is needed.