P0670 fault code: glow plug module control circuit
Plain-language definition
Glow Plug Control Module 1 Control Circuit/Open
What does it mean?
On many diesel cars, a separate glow plug control module or relay switches the high current that goes to the glow plugs. The engine computer decides when and for how long the glow plugs should heat, and sends commands to this module over a control line.
P0670 is stored when the engine computer sees a problem on this control line, for example an open circuit caused by a broken wire or an unplugged connector. So the problem isn't always in the glow plugs; it may be in the line that carries the command to the module, or in the module itself. In the definition, Module 1 refers to the first module on cars with more than one glow plug module.
If the module doesn't get the right commands, the glow plugs may not heat up as they should. So, especially in cold weather, you may notice the engine being hard to start, running unevenly and producing white smoke in the first few minutes; the check engine light or the glow plug light may come on.
How serious is it?
It's a Warning-level code. Even though the problem is in the control line, it can stop the glow plug system from working, so its effect is felt most in cold weather, when you first start the engine.
Severity is a guide; if the warning light is flashing or you notice symptoms while driving, have the car checked at a workshop.
Common general causes
- A broken or damaged wire between the engine computer and the glow plug module
- A loose or corroded module connector
- A faulty glow plug control module (or relay)
- A problem with the module's power supply or ground connection, or a blown fuse
- Less often, problems coming from the engine computer (ECU)
The list shows general causes; a workshop finds the actual cause on your car with a check.
Definitions by make
Some manufacturers record the same code under their own wording:
- Fiat
- No power control unit plugs,
Related codes
How does it appear in the 2dakika report?
Glow Plug Control Module 1 Control Circuit/Open
If the code is read as a confirmed (stored) fault, the report shows it with the "Warning" severity; in pending or past records, codes that don't request the warning light and aren't critical appear as "Info". If the engine computer stored them, the conditions when the fault was recorded (engine temperature, rpm, speed) are shown too.
Read this code with the OBD-X1, and clear it from the app after the repair.
Clearing the code doesn't fix the fault; if the problem persists, the code comes back.