P0670

Glow Plug Module Control Circuit

P0670 is a generic OBD-II powertrain diagnostic trouble code: Glow Plug Module Control Circuit. It is logged by the engine control unit when the glow monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.

Code
P0670
Group
Powertrain
System
Glow
Severity
Warning (MIL on)
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What P0670 means

Code P0670 is a generic SAE OBD-II fault that sets when the powertrain control module (PCM) detects an electrical malfunction in the glow plug control module (GPCM) control circuit. The glow plug system is critical to diesel engine operation: glow plugs pre-heat each cylinder's pre-combustion chamber so that compression-ignition can occur reliably, particularly during cold ambient temperatures.

The fault can originate anywhere along the control path — from the fuse/relay that powers the module, through the wiring harness and connector pins, inside the GPCM itself, or at the PCM's driver circuit. A faulty engine coolant temperature (ECT) sensor can also be implicated.

Because the glow plug circuit is only active below approximately 40 °C coolant temperature, symptoms may be intermittent or absent in warm climates. In cold conditions, however, a fully failed GPCM circuit can prevent engine starting entirely.

Common causes

Most-frequently reported root causes when P0670 is logged.

  • 1
    Open, shorted, or corroded wiring/connectors in the GPCM control circuit
  • 2
    Blown fuse or failed fusible link supplying the glow plug control module
  • 3
    Faulty or failed glow plug control module (GPCM)
  • 4
    Defective engine coolant temperature (ECT) sensor
  • 5
    Failed or stuck-open ignition switch not energising the glow plug relay
  • 6
    One or more failed glow plugs overloading the module output circuit
  • 7
    CAN bus communication fault between the GPCM and PCM
  • 8
    PCM internal driver failure (rare)

Symptoms drivers notice

MIL (check engine light) illuminated
Hard starting or no-start condition in cold temperatures
Extended crank time before the engine fires
White or grey exhaust smoke during cold-start warm-up
Rough idle immediately after a cold start
Reduced engine performance until normal operating temperature is reached

How to diagnose P0670

A typical diagnostic flow when this code is present.

  1. 1
    Retrieve all stored DTCs with a scan tool; note any companion codes
  2. 2
    Inspect the fuse and fusible link supplying the GPCM; replace any blown protection devices
  3. 3
    Perform a visual inspection of the GPCM connector and wiring harness for corrosion, chafing, backed-out pins, or moisture intrusion
  4. 4
    Verify battery voltage at the GPCM power supply pin and a clean ground
  5. 5
    Command the GPCM on with the scan tool (if supported) and check for the correct switched output voltage
  6. 6
    Test ECT sensor resistance and voltage output against manufacturer specifications
  7. 7
    Measure individual glow plug resistance; replace any plugs that are open-circuit

Related powertrain codes

Frequently asked questions

Can I drive with a P0670 code stored?

In warm weather the vehicle may drive normally because glow plugs are not needed once the engine is at operating temperature. However, in cold conditions the engine may refuse to start.

Will P0670 cause a no-start every time?

Not necessarily. If the glow plug system is only partially compromised, the engine may still start — just with extra cranking, white smoke, and a rough idle.

Is P0670 the same as a bad glow plug?

No. P0670 specifically flags the control circuit between the PCM and the glow plug control module.

How much does it cost to fix P0670?

A blown fuse costs under $5. A replacement GPCM typically costs $150–$400 in parts plus 1–2 hours of labour.

Disabling P0670 in software

RaceTune can permanently disable P0670 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.

Permanent
The monitor is disabled in the ECU itself — not just cleared. It cannot return.
Tailored to your file
Each patch is matched to your specific software version — never a one-size-fits-all file.
Reversible
The original file is always preserved. Reflash the stock to return the ECU to factory state.

Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.

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