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. This code is set when the Engine Control Module (ECM) detects an open or short circuit in the glow plug or its wiring. Common causes include a failed glow plug, damaged wiring, or a faulty glow plug relay. Driving with this code may cause hard starting, rough idle, and increased emissions, especially in cold weather.
1. Most Common Causes
- Faulty or burned-out glow plug in cylinder 1
- Corroded, disconnected, or shorted wiring or connector in the glow plug circuit
- Glow plug internal resistance out of specification (typically 0.5–2.0 ohms)
- Defective glow plug relay
- Failed glow plug control module
- ECM failure (less common)
2. Symptoms You Will Notice
- Hard starting, especially in cold weather
- Rough idle or misfire on cylinder 1
- Check Engine Light illuminated
- Excessive smoke from exhaust during startup
3. Step-by-Step Diagnosis
Step 1: Use a scan tool to confirm P0671 and check for other codes.
Step 2: Visually inspect the glow plug wiring and connector for damage or corrosion.
Step 3: Test the glow plug resistance with a multimeter (should be low, typically 0.5-2 ohms).
Step 4: Check voltage at the glow plug connector with the key on (should be battery voltage).
Step 5: If voltage is present and glow plug is good, test the glow plug relay and fuse.
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 may cause excessive smoke. It's best to repair promptly to avoid starting issues and potential damage to other components.
How much does it cost to fix?▼
Replacing a single glow plug typically costs $50-$150 including parts and labor. If wiring or relay replacement is needed, costs may be higher.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.