P0675

P0675 means the ECU detected a fault in the glow plug circuit feeding cylinder 4 specifically — open, short, or resistance out of spec, set by the Glow Plug Control Module during the glow cycle. The cheapest-first diagnostic ladder: (1) Pull the pigtail at cylinder 4 and ohm the plug — healthy 0.4-2.0 ohms cold (most diesels 0.6-1.2 ohms), 0 shorted, infinite open, 4+ weak. (2) Confirm the GPCM is commanding the cyl 4 channel with the expected PWM duty (0-100% scaled to coolant temp) and glow-on time (5-30 sec below 60F coolant). (3) Clamp an amp probe on the feed wire and watch for 7-20A inrush falling to 5-15A; flat 0A with command ON is an open circuit, sustained 20A+ is a short. 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 patterns: 2003-2007 Ford 6.0L Powerstroke V8 throws P0675 from cylinder 4 (passenger bank, second from front) when the FICM is borderline — cylinder 4 is one of the first to flag because of injector-driver harness routing near the EGR cooler. 2008-2010 Ford 6.4L Powerstroke commonly throws P0675 from the under-valve-cover harness fault, same pattern as P0674. 2001-2010 Duramax V8 throws P0675 with cylinder 4 on the passenger bank — LB7/LLY/LBZ glow plug failures are extremely common and GM eventually went to a higher-grade plug (use Bosch Duraterm or AC Delco OE, NOT cheap aftermarket). 2009-2016 Audi/VW 2.0 TDI EA189 4-cylinder throws P0675 as the rearmost cylinder in the inline-4 — cyl 4 sits next to the firewall, runs hottest, and tends to fail first; VW dealer typically replaces all four. 2007-2018 Cummins 6.7L inline-6 throws P0675 on cyl 4 from the same mid-block heat-soak pattern as P0674. Estimated repair: $80 (single plug, easy access) to $1,400 (full set on the Powerstroke, including UVCH harness).