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 during cold starts. In diesel engines, glow plugs are essential for ignition; a fault can cause hard starting, misfires, and increased emissions.
01. Most Common Causes
- Faulty glow plug in cylinder 3
- Open or shorted wiring in the glow plug control circuit
- Corroded or loose connector at the glow plug
- Failed glow plug control module or relay
02. Symptoms You Will Notice
- Hard starting, especially in cold weather
- Engine misfire or rough idle on cold start
- Check Engine Light illuminated
- Reduced fuel economy
03. Step-by-Step Diagnosis
Step 1: Use a scan tool to confirm P066E and check for related codes.
Step 2: Visually inspect the glow plug wiring and connector for cylinder 3 for damage, corrosion, or looseness.
Step 3: Measure resistance of the cylinder 3 glow plug; compare to spec (typically 0.5-2 ohms).
Step 4: Test voltage at the glow plug connector with key on; should be battery voltage.
Step 5: If wiring and plug are okay, test the glow plug control module/relay output.
04. Commonly Affected Makes
05. 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 may cause engine damage. It's best to repair promptly.
How much does it cost to fix?▼
Typically $50-$150 for a single glow plug replacement, including parts and labor. If wiring or module is faulty, costs may be higher.