Cylinder 1 Glow Plug Circuit Malfunction
The P0671 code indicates a fault in the glow plug circuit for cylinder 1. Glow plugs are used in diesel engines to preheat the combustion chamber for cold starts. The Powertrain Control Module (PCM) monitors the resistance of each glow plug circuit. When the resistance is out of specification (too high or too low), or there is an open or short circuit, this code is set. Common causes include a failed glow plug, damaged wiring, or a faulty glow plug relay/module.
01. Most Common Causes
- Failed glow plug in cylinder 1
- Open or short circuit in glow plug wiring
- Faulty glow plug relay or control module
- Corroded or loose connector at glow plug
02. Symptoms You Will Notice
- Hard starting, especially in cold weather
- Rough idle or misfire on cold start
- Check Engine Light illuminated
- Excessive white smoke on startup
03. Step-by-Step Diagnosis
Step 1: Use a scan tool to confirm code P0671 and check for other related codes.
Step 2: Visually inspect the glow plug wiring and connector for cylinder 1 for damage, corrosion, or looseness.
Step 3: Measure the resistance of the glow plug at cylinder 1 using a multimeter (typically 0.5-2 ohms). Compare to manufacturer specs.
Step 4: If glow plug is good, test the voltage supply at the glow plug connector with the key on/engine off (should be battery voltage).
Step 5: If voltage is missing, check the glow plug relay, fuse, and control module.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
You can drive short distances in warm weather, but cold starts will be difficult. Prolonged driving may cause incomplete combustion and damage the catalytic converter.
How much does it cost to fix?▼
Replacing a single glow plug costs $50-$150 including parts and labor. If wiring or relay needs repair, costs may be higher.