Common Symptoms
- Hard starting or extended cranking in cold weather
- White smoke from exhaust on cold start
- Rough idle until engine warms up
- Glow plug warning light illuminated on dash
- Engine misfires on cylinder 1 during warm-up
Most Likely Root Causes
- Failed glow plug on cylinder 1
- Open or short circuit in glow plug wiring harness
- Corroded or loose glow plug connector
- Failed glow plug control module or relay
- High resistance in ground circuit
Full step-by-step tests, DVOM guidance, and pinout data are available inside the AI Diesel Tech diagnostic session.
AI walks you through every test — one step at a time. Plans start at $12.95/mo.
Component Location
Cylinder 1 glow plug is threaded into the cylinder head near the fuel injector on the number one cylinder.
Manufacturer Notes
Some diesel engines require glow plug replacement as a complete set to ensure consistent heat-up characteristics across all cylinders.
Also diagnosing J1939 SPN/FMI codes?
Heavy-duty trucks often throw both OBD-II and J1939 faults simultaneously. AI Diesel Tech handles both protocols in a single guided session.
AI Diesel Tech — The Technician's Diagnostic Engine
AI Diesel Tech diagnostic logic is built by an ASE Certified Diesel Technician. Professional-grade OBD-II and J1939 fault analysis — trusted by technicians nationwide, used in shops, fleets, and training programs.
Get AI-Guided Diagnosis for P0671
The diagnostic engine walks you through every physical test — step by step, on your phone, at the truck.