What is a glow plug control module?

It is an electronic module that controls glow plug activation, duration, and current. It communicates with the ECU and can monitor each plug individually for faults.

Can I drive with P0670?

Yes, but cold starting will be poor and emissions will be high. In very cold weather the vehicle may be difficult or impossible to start.

How much does a glow plug module cost?

Glow plug modules typically cost £80–£250 depending on vehicle. Labour is moderate — the module is usually accessible but testing is important before replacement.

Will new glow plugs fix P0670?

Not necessarily. P0670 is a module circuit fault. If the plugs themselves have failed and damaged the module, you will need both new plugs and a new module.

How do I know if my glow plug module has failed?

Symptoms include all glow plugs failing simultaneously, no glow plug warning light at all (module not powering up), and an OBD scanner showing no communication with the GPCM.

Does P0670 affect starting in summer?

Minimally. Glow plugs are only critical for cold starting. In warm weather, diesel ignites more easily and the impact of a faulty glow plug system is much less noticeable.

P0670 — Fault Code | Mr Auto Fixer

What Is P0670?

P0670 is a diesel-specific fault indicating a problem with the glow plug module control circuit. Unlike older diesels where glow plugs were directly switched by the ignition, modern vehicles use a dedicated glow plug control module (GPCM) that precisely controls glow plug timing and duration. P0670 means the ECU cannot communicate with or control this module correctly.

This fault affects cold starting performance significantly, especially in winter. Without correctly functioning glow plugs, diesel combustion is poor when cold, leading to hard starting, white smoke, and rough running until the engine warms up.

Common Symptoms

Glow plug warning light stays on or flashes
Hard starting in cold weather
White smoke from exhaust on cold start
Rough running until engine is fully warm
Engine management light on
Multiple glow plug circuit codes alongside P0670

Common Causes

Failed glow plug control module (GPCM)

Open or short circuit in the CAN bus or signal wire between ECU and GPCM

Poor power supply or earth to the glow plug module

Failed glow plugs overloading and damaging the module

Corroded connector at the glow plug module

ECU fault affecting the module control output

How to Diagnose P0670

Check for Individual Glow Plug Codes

Scan for codes P0671–P0674 alongside P0670. Individual glow plug circuit codes suggest the module is functioning but individual plugs have failed. P0670 alone, without individual codes, suggests the module or its wiring is the fault.

Inspect the GPCM Connector

Locate the glow plug control module (usually on the cylinder head or valve cover area). Disconnect and inspect the connector for corrosion, loose pins, or heat damage.

Check Module Power Supply

Test for battery voltage at the GPCM main supply pin with ignition on. Also verify a good earth connection — without proper power and earth, the module cannot operate.

Test Module Communication

Using an advanced scanner, check if the ECU can communicate with the GPCM via the network. No communication at all indicates a wiring fault or failed module.

Check Individual Glow Plug Resistance

With the glow plug wiring disconnected, test each glow plug resistance. Healthy plugs read 0.5–2 ohms. Open circuit (infinite) or very low resistance (short) indicates a failed plug that may have damaged the module.

Replace the GPCM

If power, earth, and wiring check out, the module itself has failed. On some vehicles the module is integrated with a controller — consult the vehicle-specific wiring diagram before ordering parts.

Module vs PlugsIt is common for multiple glow plugs to fail on high-mileage diesels and take out the control module with them. When replacing the module, always check and replace any failed glow plugs at the same time — fitting a new module with faulty plugs will damage the replacement.

Verdict

Check individual glow plug codes first. If present, address the plugs before the module. If P0670 appears alone, focus on the GPCM power supply and wiring before replacing the module.

P0670 — Fault Code