Cylinder 2 Glow Plug Control Circuit Low
The P066C code indicates that the engine control module (ECM) has detected a low voltage condition in the glow plug control circuit for cylinder 2. This circuit controls the glow plug used to preheat the combustion chamber for cold starts. A low voltage reading suggests a short to ground, open circuit, or faulty component in the glow plug system, which can lead to hard starting, misfires, and increased emissions, especially in cold weather.
1. Most Common Causes
- Cylinder 2 glow plug has an internal short circuit or low resistance
- Control circuit wiring shorted to ground
- Corroded, loose, or damaged connector or terminal
- Faulty glow plug control module (GPCM)
- Excessive circuit resistance due to deteriorated wiring or splices
- Intermittent wiring harness failure caused by vibration or excessive heat
2. Symptoms You Will Notice
- Hard starting, especially in cold weather
- Engine misfire or rough idle
- Check Engine Light illuminated
- Excessive smoke from exhaust on startup
3. Step-by-Step Diagnosis
Step 1: Scan the vehicle for codes and record freeze frame data.
Step 2: Visually inspect the glow plug wiring and connector for cylinder 2 for damage or corrosion.
Step 3: Measure resistance of the cylinder 2 glow plug; compare to manufacturer specs (typically 0.5-2 ohms).
Step 4: Check voltage at the glow plug connector with key on; should be battery voltage (12V).
Step 5: Test the glow plug control module/relay for proper operation and output.
4. 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, poor engine performance, and potential damage to the catalytic converter from unburned fuel.
How much does it cost to fix?▼
The cost to fix P066C typically ranges from $50 to $150 for parts and labor, depending on whether the glow plug, wiring, or control module needs replacement.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.