Cylinder 1 Glow Plug Control Circuit Low
The P066A code indicates that the Engine Control Module (ECM) has detected a low voltage condition in the glow plug control circuit for cylinder 1. This circuit is responsible for energizing the glow plug to aid cold starts. A low voltage reading suggests excessive resistance, a short to ground, or a faulty glow plug or control module. This can lead to hard starting, misfires, and increased emissions, especially in cold weather.
01. Most Common Causes
- Faulty glow plug in cylinder 1
- Open or shorted glow plug wiring or connector
- Failed glow plug control module or relay
- Corrosion or damage in the glow plug circuit
02. Symptoms You Will Notice
- Hard starting, especially in cold weather
- Engine misfire or rough idle
- Check Engine Light illuminated
- Excessive white smoke from exhaust on startup
03. Step-by-Step Diagnosis
Step 1: Scan for codes and record freeze frame data.
Step 2: Visually inspect 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 voltage at glow plug connector with key on; should be battery voltage (12V).
Step 5: Test glow plug control module/relay output and ground circuits.
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, especially in cold weather, as it can cause hard starting, misfires, and potential damage to the catalytic converter from unburned fuel.
How much does it cost to fix?▼
The cost to fix P066A typically ranges from $50 to $150 for a glow plug replacement, but can be higher if the control module or wiring needs repair.