P0672

P0672 means the ECU detected a fault in the glow plug circuit feeding cylinder 1 specifically — typically an open circuit, a short to ground, or a resistance reading outside spec. Glow plugs are heating elements that pre-warm the combustion chamber on a diesel for cold starts, and the Glow Plug Control Module (GPCM) monitors each cylinder's circuit individually for current draw during the glow-on cycle. The cheapest-first diagnostic ladder: (1) Pull the glow plug harness connector at cylinder 1 and ohm the plug at its terminal — a healthy glow plug measures 0.4-2.0 ohms cold (most diesels land 0.6-1.2 ohms); below 0.3 ohms is shorted internally, infinite/OL is open/burned out, and 4+ ohms is a marginally weak plug that's the most common cold-start hard-start root cause. (2) Back-probe the harness side and confirm the GPCM is sending the commanded PWM signal — 0-100% duty cycle depending on coolant temp, with glow-on time typically 5-30 sec (longer below 20F, shorter above 60F). (3) Clamp an inductive amp probe over the cylinder 1 glow plug feed wire and watch current during the glow cycle — healthy plugs draw 7-20A initial inrush that falls to 5-15A as the element heats and resistance rises. A flat 0A reading with the GPCM commanding ON is an open circuit between the module and the plug (broken wire, bad connector pin, or burned-out 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 commonly throws P0672 from harness chafing where the glow plug pigtail crosses the valve cover — cylinder 1 sits at the front driver's side and sees the most heat-cycle stress; the fix is the updated International harness with sleeving plus a new plug. 2001-2010 Duramax LB7/LLY/LBZ/LMM frequently throws P0672 when the GPCM's cylinder 1 driver fails — Duramax cyl 1-7 are on the driver's bank (left front), and the GPCM lives on the passenger inner fender where it cooks in summer heat; replace the plug AND the module if amp draw is zero at the plug pigtail. 2007-2018 Dodge/RAM Cummins 6.7 inline-6 throws P0672 from the well-known glow plug harness connector corrosion at cylinder 1 (front of the head, closest to the radiator overspray); dielectric grease and a fresh OEM connector resolves it. 2007-2018 Mercedes Sprinter OM642 3.0L V6 BlueTec commonly throws P0672 from a single weak plug among six — Mercedes specs all six replaced together because mixed-age plugs cascade-fail within 6 months. Estimated repair: $80 (single plug DIY) to $1,400 (full set of 6-8 plugs plus GPCM).