Cylinder 3 Glow Plug Control Circuit Low
The P066E code indicates that the powertrain control module (PCM) has detected a low voltage condition in the glow plug control circuit for cylinder 3. This typically means the glow plug or its wiring has excessive resistance or a short to ground, preventing proper heating of the cylinder for cold starts. In diesel engines, glow plugs are essential for ignition in cold weather; a fault can cause hard starting, misfire, and increased emissions.
1. Most Common Causes
- Glow plug #3 has internal short circuit or low resistance
- Control circuit wiring shorted to ground
- Corroded, loose, or damaged connector or terminal in cylinder 3 circuit
- Faulty glow plug control module (GPCM)
- Excessive wiring resistance due to oxidation or heat damage
- Internal ECM/PCM failure (less common)
2. Symptoms You Will Notice
- Hard starting, especially in cold weather
- Engine misfire or rough idle
- Check Engine Light illuminated
- Reduced fuel economy
3. Step-by-Step Diagnosis
Step 1: Use a scan tool to confirm the code and check for related codes.
Step 2: Visually inspect the glow plug wiring and connector for cylinder 3 for damage or corrosion.
Step 3: Measure resistance of the glow plug; should be low (0.5-2 ohms). High resistance indicates a bad glow plug.
Step 4: Check voltage at the glow plug connector with key on; should be battery voltage. If low, trace circuit back to control module.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
You can drive short distances in mild weather, but cold starts will be difficult and the engine may run poorly. It's best to repair promptly to avoid further issues.
How much does it cost to fix?▼
Typically $50-$150 for a DIY glow plug replacement. Shop labor may add $100-$200, totaling $150-$350.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.