Glow Plug Module Control Circuit Malfunction
The P0670 code indicates a fault in the glow plug module control circuit, which is responsible for managing the glow plugs during cold starts in diesel engines. The Powertrain Control Module (PCM) monitors the circuit for proper voltage and current. When a malfunction is detected, such as an open or short circuit, the code is set. This can prevent the glow plugs from heating, leading to hard starting in cold weather.
1. Most Common Causes
- Faulty glow plug control module
- Damaged or corroded wiring in the control circuit between the ECM and the glow plug module
- Glow plug module connector with bent, corroded, or disconnected pins
- Short to ground or voltage in the glow plug module control circuit
- Open circuit in the glow plug module wiring
- Internal ECM/PCM failure (less common)
- Blown glow plug circuit fuse
2. Symptoms You Will Notice
- Hard starting, especially in cold weather
- Check Engine Light illuminated
- Excessive white smoke from exhaust on startup
- Rough idle or misfire until engine warms up
3. Step-by-Step Diagnosis
Step 1: Use a scan tool to confirm P0670 and check for related codes.
Step 2: Inspect the glow plug module fuse and relay; replace if blown.
Step 3: Visually inspect the wiring and connectors for damage, corrosion, or looseness.
Step 4: Test the glow plug module power and ground circuits with a multimeter.
Step 5: If circuits are okay, test the glow plug module output to the glow plugs; replace module if faulty.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
You can drive short distances in warm weather, but avoid cold starts as the engine may not start or run poorly. Prolonged driving can damage the catalytic converter due to unburned fuel.
How much does it cost to fix?▼
Diagnosis typically costs $50-$150. Replacing the glow plug module ranges from $100-$300, including parts and labor.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.