6.0L Power Stroke P0670: Causes and How to Fix It

A 6.0L Power Stroke P0670 code -- Glow Plug Module Control Circuit -- means the engine control module has detected a fault in the control circuit between the PCM and the Glow Plug Control Module (GPCM). The GPCM is a separate module on the 6.0L Power Stroke that receives a command signal from the PCM and then controls power delivery to all eight glow plugs. When P0670 is set on the 6.0L Power Stroke, it indicates the PCM cannot communicate with the GPCM correctly, the GPCM itself has failed, or the wiring between the two modules has an open or short. The result is that glow plug operation is impaired or absent, which causes hard starting in cold weather and extended cranking before the engine fires. This guide covers the causes of 6.0L Power Stroke P0670, how to confirm which component is at fault, and what the repair involves.

What P0670 Means on the 6.0L Power Stroke

P0670 is a module-level glow plug code that is distinct from the individual glow plug codes P0671 through P0678. Those codes indicate a specific glow plug has failed -- each code maps to one cylinder. P0670 is a circuit-level fault: it means the PCM detected a problem with the control signal it sends to the GPCM or in the GPCM's response. When P0670 is present, all eight glow plugs may be affected because the GPCM that controls them cannot operate correctly.

The 6.0L Power Stroke GPCM is mounted under the hood and serves as the power switching module for the glow plug circuit. The PCM sends a low-current command signal to the GPCM, and the GPCM switches the high-current power to the glow plugs in response. The GPCM also monitors glow plug resistance and reports individual plug faults back to the PCM. When the GPCM fails -- either from internal failure or from damage caused by a shorted glow plug drawing excessive current -- the PCM loses the expected communication and sets P0670.

Individual glow plug failure is a common cause of GPCM damage on the 6.0L Power Stroke. When a glow plug shorts internally, it draws far more current than the GPCM is rated for. Over time, or in a single severe event, this excess current can damage the GPCM's internal switching components. A 6.0L Power Stroke that develops P0670 after a history of individual glow plug codes has almost certainly had a shorted plug damage the GPCM. Replacing only the GPCM without replacing the glow plugs -- particularly any that have shorted -- will result in the new GPCM failing for the same reason.

Fitment: 6.0L Power Stroke P0670 Applies to These Trucks

• 2003-2007 Ford F-250 Super Duty with 6.0L Power Stroke diesel (International VT365)
• 2003-2007 Ford F-350 Super Duty with 6.0L Power Stroke diesel
• 2003-2007 Ford F-450 and F-550 Super Duty with 6.0L Power Stroke diesel
• 2003-2007 Ford Excursion with 6.0L Power Stroke diesel

The GPCM location and connector differ slightly between 2003-2004 and 2005-2007 production, and glow plug part numbers changed with the updated 6.0L calibration. Confirm the model year when sourcing GPCM and glow plug replacement parts.

Top Picks: 6.0L Power Stroke P0670 Repair Parts

Any 6.0L Power Stroke P0670 repair that involves GPCM replacement should include a full glow plug inspection and replacement of any plugs that are out of spec. Shorted or high-resistance glow plugs are the most common cause of GPCM failure -- replacing the GPCM without addressing failed plugs exposes the new module to the same damaging current condition. The 6.0L Power Stroke Glow Plug Kit 2003-2007 replaces all eight glow plugs in a single service, eliminating any marginal or shorted plug as a contributing factor before the GPCM is installed. A full set replacement at the time of GPCM service is the correct procedure on any 6.0L Power Stroke with P0670 and unknown plug history.

For a P0670 accompanied by individual glow plug harness codes or visible wiring damage at the plug connectors, the 6.0L Power Stroke Glow Plug Kit 2003-2007 with Harness provides both the replacement glow plugs and the wiring harness needed to address connector or pigtail damage at the same time. Harness damage at the glow plug connectors is a secondary cause of P0670 -- damaged wiring between the GPCM and the individual plugs causes the module to detect abnormal circuit conditions and can set both individual plug codes and the module-level P0670. Browse the complete Power Stroke glow plug and starting system catalog for glow plug kits, harness kits, and GPCM replacement options.

Match to the Build

The correct diagnostic path for 6.0L Power Stroke P0670 depends on what accompanying codes are present and what the GPCM circuit tests reveal:

• P0670 with individual glow plug codes (P0671-P0678): The GPCM detected a fault in at least one specific plug circuit. Those plugs should be tested and replaced as part of the P0670 repair. A GPCM that has been managing shorted plugs will likely need replacement too -- test the GPCM after plug replacement before clearing codes.
• P0670 alone with no individual plug codes: A standalone P0670 is more consistent with a GPCM power or communication fault. Check fuse and relay supply to the GPCM first -- a blown supply fuse produces P0670 without individual plug codes because the module has no power to run the plug diagnostic. Confirm supply voltage before condemning the module.
• P0670 with hard start in cold weather only: A stored P0670 with acceptable warm-weather starting confirms the glow plug circuit is non-functional. The 6.0L Power Stroke requires functional glow plugs below approximately 40 degrees Fahrenheit -- address P0670 before cold-weather operation.
• P0670 on a truck with known oil cooler or EGR issues: Repeated coolant contamination events from a failed oil cooler can cause moisture intrusion in the GPCM. Inspect the GPCM connector for corrosion or moisture damage before assuming the module itself has failed internally.

Signs the Glow Plug System Needs Attention

• Extended crank time before the engine fires in temperatures below 50 degrees Fahrenheit -- the clearest symptom of a non-functional glow plug circuit; a healthy 6.0L Power Stroke starts promptly in cold weather when glow plugs are operating
• White smoke from the exhaust on a cold start that persists longer than normal -- incomplete combustion from insufficient pre-heat; characteristic of missing glow plug function
• P0671 through P0678 codes appearing before or alongside P0670 -- individual plug failures that preceded GPCM damage; a truck with a history of multiple individual plug codes is a candidate for GPCM failure
• GPCM supply fuse blown -- found during the fuse inspection step; replace the fuse after confirming the plug fault is corrected
• Cold start rough idle that smooths out at operating temperature -- early glow plug degradation before full failure; weak plugs cause inconsistent pre-heat and rough cold starts before the GPCM detects a fault

Frequently Asked Questions

Can I drive a 6.0L Power Stroke with P0670?

In warm weather the truck may start and run acceptably with P0670 because combustion temperature compensates for the missing glow plug pre-heat. In cold weather -- below approximately 40 degrees Fahrenheit -- a non-functional glow plug circuit causes hard start, extended crank, and potential no-start conditions. Address P0670 before cold-weather operation; the GPCM and glow plugs are not components that can be deferred through a winter season.

How do I test the GPCM on a 6.0L Power Stroke?

Confirm GPCM supply voltage and ground at the module connector with the ignition in the run position. If supply voltage is present and ground is confirmed, send a command signal from a scan tool or by cycling the key to the run position for the normal glow plug pre-heat period. A functioning GPCM should switch voltage to the glow plug rail during the pre-heat cycle. If the GPCM does not switch output with confirmed supply and command signal, the module is failed and requires replacement.

Do I need to replace all eight glow plugs for P0670?

On a high-mileage 6.0L Power Stroke with unknown glow plug history, replacing all eight at the time of GPCM service is strongly recommended. Individual plug testing can identify which plugs are currently out of spec, but a full set replacement ensures no marginal plugs remain to damage the new GPCM. The labor to access glow plugs on the 6.0L Power Stroke is the same whether one or all eight are replaced -- a full set at the time of GPCM service is the efficient and complete repair.

Bottom Line

A 6.0L Power Stroke P0670 is a glow plug module circuit fault that requires confirming GPCM power supply, checking for individual plug failures that may have damaged the module, and replacing both the GPCM and any failed glow plugs as part of the complete repair. On any 6.0L Power Stroke with P0670 and unknown plug history, a full glow plug set replacement alongside the GPCM is the correct procedure to prevent the new module from experiencing the same current overload that likely caused the original failure.