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DTC codes / P06xx · Computer and output circuits / P0670

P0670Glow Plug Module Control Circuit

P0670 is a generic OBD-II code indicating that the engine control module (ECM) has detected an open, short, or out-of-range condition on the control circuit for the glow plug module, which is the electronic unit that regulates power to the glow plugs on diesel engines. The ECM monitors the voltage or current on the command wire to the module and sets this code when the signal does not match expected values during the glow plug pre-heat or post-heat phase.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaComputer and output circuits

Symptoms you may notice

  • Illuminated check engine light, often with no other noticeable symptoms.
  • Hard cold starting or extended cranking before the engine fires, especially in low temperatures.
  • Rough idle and white smoke from the exhaust immediately after a cold start.
  • Reduced engine performance and poor fuel economy during warm-up.
  • A stored glow plug module control circuit code that may be intermittent in wet or cold weather.

Common causes, most likely first

  1. Damaged or corroded wiring or connector terminals on the glow plug module control circuit.
  2. Failed glow plug control module, often due to internal electronics or water intrusion.
  3. Blown fuse or faulty relay that supplies power to the glow plug module.
  4. Open or shorted control wire between the ECM and the glow plug module.
  5. Poor ground connection for the glow plug module or engine block.
  6. Faulty ECM driver circuit, though this is less common and should be confirmed last.

How to diagnose and fix it

  1. Scan all modules for stored codes and record freeze-frame data to understand when the fault occurs.
  2. Visually inspect the glow plug module, its connectors, and the control circuit wiring for corrosion, chafing, or loose pins.
  3. Check the fuse and relay that feed power to the glow plug module, and test for voltage at the module connector with the key on.
  4. Measure resistance and continuity on the control wire between the ECM and the glow plug module to rule out opens or shorts.
  5. Perform a voltage drop test on the module ground circuit to ensure a clean, low-resistance path to the battery negative.
  6. If all wiring and power supplies check out, substitute a known-good glow plug module and clear the code to see if it returns.
  7. As a final step, verify the ECM control signal with an oscilloscope or bidirectional scan tool before condemning the ECM.

What the glow plug module code hides

  • A P0670 can be set by a weak or failing battery because low cranking voltage disrupts the module's self-test, so always load-test the battery before replacing parts.
  • Corroded terminals inside the glow plug module connector are a frequent cause that visual inspection from outside often misses, so unplug and inspect the pins closely.
  • The code does not always mean the module itself has failed; a shorted glow plug can back-feed the control circuit and trigger P0670 without any module fault.
  • On many vehicles the glow plug module shares a ground with other engine sensors, so a single bad ground can set P0670 along with unrelated codes.
  • Intermittent P0670 codes that appear only in damp weather often trace to water ingress in the module connector or a chafed wire loom near the engine.

Can I keep driving with P0670?

You can usually drive the vehicle with P0670, but cold starting will be harder and the engine may run rough with excess smoke until it warms up. Avoid heavy loads and long idling in cold weather, and repair the fault before winter to prevent glow plug and starter wear.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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