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OBD-II Code

P0677

Severity

Not yet reviewed

Nobody on our side has assessed this code yet, so we are not going to guess at how serious it is.

Can you drive it

We cannot say

Treat it as unknown until a shop reads it with live data. If the check-engine light is FLASHING, stop driving as soon as it is safe to — that means an active misfire, whatever the code.

Indicative cost (USD)

$120–$1,600

From this code's diagnostic notes. Varies by vehicle, diagnosis, parts, and local labor. This is not a repair quote.

$120 (single plug with extended labor) to $1,600 (full set on the Cummins).

P0677 means the ECU detected a glow plug circuit fault on cylinder 6 — open, short, or resistance out of spec per the GPCM.

How a shop works this

Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed.

  1. Note every code that is set, not just this one.

    Codes that appear together usually narrow the cause faster than any one of them read alone.

  2. Read the freeze frame — the conditions the fault was recorded under.

    Cold or warm, idle or load, road speed and engine speed. A fault that only appears cold is a different fault from one that only appears under load, even with the same code on the scanner.

  3. Confirm the fault is current rather than history.

    Clear the code and see whether it returns under those same conditions. A code that does not come back may have been logged during a repair, a flat battery, or a bad connection that has since been disturbed.

  4. Then follow the diagnostic notes further down this page, in the order they are written.

    They are written in the order a shop works this code, cheapest checks first. Where they name a component, inspect its wiring and connector before replacing it.

If the code comes back after a repair, the underlying fault is still there. That is the point to bring in a scanner with live data and freeze-frame, or a shop that has one.

Common symptoms

  • Check engine light
Read the full diagnostic procedureP0677 means the ECU detected a glow plug circuit fault on cylinder 6 — open, short, or resistance out of spec per the GPCM.

P0677 means the ECU detected a glow plug circuit fault on cylinder 6 — open, short, or resistance out of spec per the GPCM.

The cheapest-first diagnostic ladder

  1. Ohm the cyl 6 plug at its terminal — healthy 0.4-2.0 ohms cold (most diesels 0.6-1.2 ohms), 0 shorted, infinite open, 4+ weak.
  2. Verify the GPCM is commanding cyl 6 at the expected PWM duty (0-100%) with glow-on time 5-30 sec scaled to coolant temp.
  3. Amp probe on cyl 6 feed should show 7-20A initial draw falling to 5-15A as plug heats; flat 0A with command ON = open circuit, sustained 20A+ = short. Cylinder 6 implies inline-6, V6, V8, or V10 architecture. Test resistance INDIVIDUALLY at the glow plug terminal — pulling a shorted plug measures 0 ohms; an open plug measures infinite; a marginally weak plug measures 4+ ohms cold and is the most common cold-start hard-start root cause. Replace as a set on diesel engines — mixed-age plugs cause progressive failure.
Vehicle-specific patterns2003-2007 Ford 6.0L Powerstroke V8 throws P0677 from cylinder 6 (passenger bank, third from front) — same EGR-cooler proximity as cyl 5; cyl 6 is als…
  • 2003-2007Ford 6.0L Powerstroke V8 throws P0677 from cylinder 6 (passenger bank, third from front) — same EGR-cooler proximity as cyl 5; cyl 6 is also where the FICM injector driver harness frequently chafes through.
  • 2008-2010Ford 6.4L Powerstroke throws P0677 from the under-valve-cover glow plug harness fault.
  • 2001-2016Duramax V8 throws P0677 on cyl 6 (passenger bank) — LMM and LML are slightly more durable than LB7/LLY but still throw the code on plug fatigue around 100k miles.
  • 2007-2018Cummins 6.7 inline-6 throws P0677 on the rearmost cylinder of the block (cyl 6, right against the firewall) — this is the hardest plug to reach on the 6.7 because the cab tilts forward only on Class 7+ trucks; on Dodge/RAM 2500/3500, expect 1.5 hr labor just to access cyl 6.
  • 2007-2018Mercedes Sprinter OM642 V6 uses cyl 6 as the rearmost passenger-bank cylinder and routinely throws P0677 from poor cooling around the turbocharger heat shield.

Estimated repair$120 (single plug with extended labor) to $1,600 (full set on the Cummins).

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