Diesel Trouble Codes
Plain-English diesel fault-code and symptom diagnostics: what a code means, the likely causes in order, how to check each one, and when to see a pro.
Free diagnostic guides for diesel trouble codes and symptoms — Ford Power Stroke, Ram Cummins, GM Duramax, and the International DT466E, Cummins ISX15 and Detroit DD15. No signup and no paywall; the site is supported by ads and affiliate links. Who runs this site.
Every guide follows the same order a good technician works in: what the code or symptom actually means, the likely causes ranked from most to least common, how to check each one with basic tools, roughly what the fix costs, and the point where it makes sense to hand it to a shop.
No emissions-delete instructions. No torque-by-torque teardowns of safety-critical systems. Just diagnosis you can trust before you start buying parts.
Engine platforms
- 5.9L Cummins 24-Valve (VP44) Diagnostics 1998.5–2002 26 guides
- 5.9L Cummins Common Rail Diagnostics 2003–2007 28 guides
- 6.0L Power Stroke Diagnostics (2003.5–2007) 2003.5–2007 25 guides
- 6.4L Power Stroke Diagnostics (2008–2010) 2008–2010 33 guides
- 6.7L Cummins Diagnostics (2007.5–2012, EGR + DPF) 2007.5–2012 32 guides
- 6.7L Cummins Diagnostics (2013–present, SCR / DEF) 2013–present 35 guides
- 6.7L Power Stroke Diagnostics 2011–present 39 guides
- 7.3L Power Stroke Diagnostics (1999–2003 Super Duty) 1999–2003 32 guides
- Cummins ISX15 Diagnostics (2010–2017) 2010–2017 30 guides
- Detroit DD15 Diagnostics (2010–present) 2010–present 12 guides
- International DT466E Diagnostics (1996–2003) 1996–2003 34 guides
- L5P Duramax Diagnostics 2017–present 33 guides
- LB7 Duramax Diagnostics 2001–2004 29 guides
- LLY / LBZ / LMM Duramax Diagnostics 2004.5–2010 34 guides
Browse by symptom
Not sure which code to look up? Start from what the truck is doing.
5.9L Cummins 24-Valve (VP44) Diagnostics
- Engine Stalls or Dies While Driving — 5.9 Cummins 24-Valve (VP44)
- Hard Start or No Start — 5.9 Cummins 24-Valve (VP44)
- Loss of Power or Dead Pedal — 5.9 Cummins 24-Valve (VP44)
- Surging or Bucking — 5.9 Cummins 24-Valve (VP44)
- White Smoke or Rough Running on Cold Start — 5.9 Cummins 24-Valve (VP44)
5.9L Cummins Common Rail Diagnostics
- Engine Stalls or Dies While Driving — 5.9 Cummins Common Rail
- Hard Start or No Start — 5.9 Cummins Common Rail
- Loss of Power or Limp Mode — 5.9 Cummins Common Rail
- Rough Idle, Misfire or Injector Knock — 5.9 Cummins Common Rail
- Surging or Erratic Throttle Response — 5.9 Cummins Common Rail
- White Smoke or Rough Running on Cold Start — 5.9 Cummins Common Rail
6.0L Power Stroke Diagnostics (2003.5–2007)
- Coolant Loss or Pressurized Coolant Bottle — 6.0 Power Stroke
- Engine Stalls or Dies While Driving — 6.0 Power Stroke
- Hard Start, Long Crank or No Start — 6.0 Power Stroke
- Loss of Power or Surging — 6.0 Power Stroke
- Oil Temperature Much Higher Than Coolant Temperature — 6.0 Power Stroke
- Rough Idle and White Smoke on Cold Start — 6.0 Power Stroke
6.4L Power Stroke Diagnostics (2008–2010)
- Black Smoke From the Exhaust — 6.4 Power Stroke
- Coolant Loss or White Smoke From the Exhaust — 6.4 Power Stroke
- Frequent or Failed DPF Regenerations — 6.4 Power Stroke
- Fuel in the Oil or Rising Oil Level — 6.4 Power Stroke
- Hard Start or No Start — 6.4 Power Stroke
- Loss of Power or Limp Mode — 6.4 Power Stroke
- Rough Idle or Misfire — 6.4 Power Stroke
6.7L Cummins Diagnostics (2007.5–2012, EGR + DPF)
- Black Smoke Under Load — 6.7 Cummins (EGR + DPF, pre-SCR)
- Engine Stalls or Dies While Driving — 6.7 Cummins (EGR + DPF, pre-SCR)
- Frequent DPF Regenerations — 6.7 Cummins (EGR + DPF, pre-SCR)
- Hard Start or Long Crank — 6.7 Cummins (EGR + DPF, pre-SCR)
- Loss of Power or Limp Mode — 6.7 Cummins (EGR + DPF, pre-SCR)
- Rough Idle and White Smoke on Cold Start — 6.7 Cummins (EGR + DPF, pre-SCR)
6.7L Cummins Diagnostics (2013–present, SCR / DEF)
- Black Smoke Under Load — 6.7 Cummins (SCR / DEF)
- DEF Warning or Speed Limit Derate — 6.7 Cummins (SCR / DEF)
- Frequent DPF Regenerations — 6.7 Cummins (SCR / DEF)
- Hard Start or Long Crank — 6.7 Cummins (SCR / DEF)
- Loss of Power or Limp Mode — 6.7 Cummins (SCR / DEF)
- Rough Idle and White Smoke on Cold Start — 6.7 Cummins (SCR / DEF)
6.7L Power Stroke Diagnostics
- Black Smoke Under Load — 6.7 Powerstroke
- DEF Warning or Speed Limit Countdown — 6.7 Powerstroke
- Engine Stalls or Dies While Driving — 6.7 Powerstroke
- Frequent DPF Regenerations — 6.7 Powerstroke
- Hard Start or Long Crank — 6.7 Powerstroke
- Loss of Power or Limp Mode — 6.7 Powerstroke
- Rough Idle and White Smoke on Cold Start — 6.7 Powerstroke
7.3L Power Stroke Diagnostics (1999–2003 Super Duty)
- Engine Stalls or Dies, Often When Hot — 7.3 Power Stroke
- Hard Start or Long Crank — 7.3 Power Stroke
- Loss of Power — 7.3 Power Stroke
- Rough Idle and White Smoke on Cold Start — 7.3 Power Stroke
- Surging or Bucking — 7.3 Power Stroke
Cummins ISX15 Diagnostics (2010–2017)
- DEF Derate or 5 MPH Speed Limit — Cummins ISX15
- Frequent Regens or High DPF Soot Load — Cummins ISX15
- Hard Start or No Start — Cummins ISX15
- Loss of Power — Cummins ISX15
- Overheating or EGR Cooler Problems — Cummins ISX15
Detroit DD15 Diagnostics (2010–present)
- Derate to 5 MPH (SCR / DEF Fault) — Detroit DD15
- EGR Flow Problems — Detroit DD15
- Frequent Regens or DPF Restriction — Detroit DD15
- Hard Start or Stalling — Detroit DD15
- Loss of Power — Detroit DD15
International DT466E Diagnostics (1996–2003)
- Engine Stalls or Dies — International DT466E
- Hard Start or No Start — International DT466E
- Loss of Power — International DT466E
- Low Oil Pressure Warning — International DT466E
- Overheating — International DT466E
- Rough Running or Misfire — International DT466E
L5P Duramax Diagnostics
- DEF Warning or Speed Limit Countdown — L5P Duramax
- Engine Stalls or Dies While Driving — L5P Duramax
- Frequent DPF Regenerations — L5P Duramax
- Hard Start or Long Crank — L5P Duramax
- Loss of Power or Limp Mode — L5P Duramax
- Rough Idle and White Smoke on Cold Start — L5P Duramax
LB7 Duramax Diagnostics
- Engine Stalls or Dies While Driving — LB7 Duramax
- Fuel in the Oil or Rising Oil Level — LB7 Duramax
- Hard Start or Long Crank — LB7 Duramax
- Loss of Power Under Load — LB7 Duramax
- Reduced Power or Poor Throttle Response — LB7 Duramax
- Rough Idle, Misfire or Smoke — LB7 Duramax
LLY / LBZ / LMM Duramax Diagnostics
- Black Smoke Under Load — LLY / LBZ / LMM Duramax
- Frequent DPF Regenerations (LMM) — LLY / LBZ / LMM Duramax
- Hard Start or Long Crank — LLY / LBZ / LMM Duramax
- Loss of Power or Limp Mode — LLY / LBZ / LMM Duramax
- Overheating When Towing — LLY / LBZ / LMM Duramax
- Rough Idle or Misfire — LLY / LBZ / LMM Duramax
- White Smoke or Rough Running on Cold Start — LLY / LBZ / LMM Duramax