What Does P0670 Mean?
The glow plug module control circuit has a general malfunction. The glow plug module (also called the glow plug relay or glow plug controller) manages the timing and power delivery to all glow plugs in the diesel engine. When this circuit fails, none of the glow plugs may receive power, making cold starting very difficult or impossible. The driver will notice the glow plug indicator light may not illuminate or may stay on continuously, and the engine will be very hard to start in cold weather.
Common Causes
35%
Failed glow plug control module/relay
25%
Wiring fault between PCM and glow plug control module
20%
Poor power supply or ground to the glow plug module
15%
One or more shorted glow plugs overloading the module
5%
PCM communication fault with glow plug module
Diagnostic Steps
1
Check for power supply to the glow plug control module — it typically receives battery voltage directly through a high-current fuse or fusible link. Verify the fuse is intact and measure voltage at the module power input.
2
Verify the ground connection for the glow plug module — clean and tighten the ground bolt. Measure voltage drop across the ground circuit (spec: less than 0.2V under load).
3
Check the control signal from the PCM to the glow plug module — with the key on and engine off (during glow cycle), verify the PCM sends a command signal (typically a ground pulse or PWM signal).
4
Disconnect all glow plugs and measure each individually. A single shorted glow plug can overload and damage the control module. Replace any shorted plugs before replacing the module.
5
If power, ground, and control signals are all present and correct, the glow plug module itself is faulty. When replacing, verify the part number matches the application — modules are calibrated for specific glow plug types and counts.
6
After replacement, verify all glow plugs cycle properly by monitoring current draw during the glow cycle using a clamp ammeter on the main power feed.
Estimated Repair Cost
$150 - $600
Parts + labor, varies by vehicle and location
The glow plug module control circuit has a general malfunction. The glow plug module (also called the glow plug relay or glow plug controller) manages the timing and power delivery to all glow plugs in the diesel engine. When this circuit fails, none of the glow plugs may receive power, making cold ...
The most common cause of P0670 (Glow Plug Module Control Circuit More details...) is: Failed glow plug control module/relay
Typical repair costs for P0670 range from $150 to $600, depending on the vehicle, location, and whether you do it yourself or go to a shop.
In warm weather, the engine will likely start without glow plugs, but in cold weather, starting may be impossible. Extended cranking without glow plug heating can wash cylinder walls with unburned fuel, diluting engine oil. Have this repaired before cold weather to avoid no-start situations and potential engine damage from oil dilution.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0670 to identify the root cause.
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Quick Info
Category
Powertrain
System
Diesel Glow Plug System
Difficulty
Type
Generic (SAE)
Recommended Tools
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