P0673

P0673 means the ECU detected a fault in the glow plug circuit feeding cylinder 2 specifically — open circuit, short to ground, or resistance out of spec, flagged by the Glow Plug Control Module during the cold-start glow cycle. The cheapest-first diagnostic ladder is identical to any per-cylinder glow code: (1) Pull the glow plug harness connector at cylinder 2 and ohm the plug at its terminal — healthy plug reads 0.4-2.0 ohms cold (typical 0.6-1.2 ohms), 0 ohms means shorted, infinite/OL means open/burned, 4+ ohms means marginally weak and is the most common cold-start hard-start root cause. (2) Verify the GPCM is sending the PWM command at 0-100% duty cycle with glow-on time of 5-30 sec scaled to coolant temp — below 20F coolant the glow cycle runs the full 30 sec, above 60F it may only run 5-8 sec. (3) Clamp an inductive amp probe on the cylinder 2 glow plug feed and look for 7-20A initial inrush falling to 5-15A as the plug heats. A reading of 0A with the GPCM commanded ON points to an open between module and plug (bad wire, broken pin, dead plug); a steady 20A+ that won't drop points to a shorted plug. 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 P0673 from cylinder 2 (passenger front) when the FICM voltage drops under 45V and starves the GPCM logic; check FICM voltage on the scan tool before condemning the plug. 2001-2010 Duramax LB7/LLY/LBZ V8 throws P0673 with cylinder 2 on the passenger bank — Duramax uses an alternating bank layout (cyl 1-3-5-7 driver, 2-4-6-8 passenger), so a P0673 sends you to the right-front cylinder, not next to P0672; the EGR cooler overhang traps heat over cylinder 2 and toasts the pigtail. 2007-2018 Cummins 6.7L inline-6 throws P0673 from harness corrosion at the front of the head where road salt and washer-fluid overspray collect. 2009-2016 Audi/VW 2.0 TDI EA189 4-cylinder (Jetta, Passat, A3) throws P0673 most often after a Dieselgate-era emissions remap stresses the glow plugs harder; VW TSBs reference replacing all four together. Estimated repair: $80 (single plug DIY) to $1,400 (full set plus GPCM).