Cylinder 2 Glow Plug Control Circuit Low
The P066C code indicates that the powertrain control module (PCM) has detected a low voltage condition in the glow plug control circuit for cylinder 2. This typically means the circuit resistance is too high or there is a short to ground, preventing the glow plug from heating properly. Common causes include a faulty glow plug, damaged wiring or connector, or a failed glow plug control module. This code is specific to diesel engines and can cause hard starting, especially in cold weather.
01. Most Common Causes
- Faulty glow plug in cylinder 2
- Open or shorted wiring in the glow plug circuit
- Corroded or damaged connector at the glow plug
- Failed glow plug control module or relay
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Hard starting, especially in cold weather
- Rough idle or misfire on cylinder 2
- 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 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 for voltage at the glow plug connector with the key on; should be battery voltage.
Step 5: If voltage is low, test the glow plug control module and relay.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
You can drive short distances, but starting may be difficult, especially in cold weather. Continued driving may cause increased emissions and potential damage to the glow plug system. It's best to repair promptly.
How much does it cost to fix?▼
Typically $50-$150 for parts and labor. A single glow plug costs $20-$50, and labor is about $30-$100 depending on accessibility.