Diesel Repair Blog — Page 2
Long-form field guides for heavy-duty trucks — written for drivers and shop techs who need practical answers. Looking for a specific code? Search the diesel fault code library.
Showing 13–24 of 119 articles
Diagnostics
Diesel White Smoke Under Load: Fuel, Coolant, or Regen Chemistry
White smoke under load is not one fault. Separate unburned fuel, coolant intrusion, and aftertreatment chemistry before you pull a head or DPF.
2026-08-27
Emissions
Duramax L5P DEF Light On: Codes, Timers, and What to Fix First
When a Duramax L5P DEF light turns on, prove fluid quality, dosing, and NOx conversion before the inducement timer steals power. Here is the shop-first check order.
2026-08-27
Diagnostics
How to Log Live Data for a Soft Truck Complaint (JPRO and INSITE)
Soft-truck complaints need loaded live data, not idle snapshots. Build a JPRO or INSITE log that proves boost, fuel, and aftertreatment under grade load.
2026-08-27
Emissions
Mack MP8 Aftertreatment Faults: First Checks That Save Shop Time
Mack MP8 aftertreatment stacks look noisy until you separate DPF, DEF dosing, and NOx sensor rationality. Start with these high-yield checks.
2026-08-27
Diagnostics
Power Stroke 6.7 Glow Plug Codes: Diagnose Before Replacing the Harness
6.7 Power Stroke glow plug and module codes often start as open circuits or harness chafe. Test plugs and control side before a full harness R&R.
2026-08-27
Diagnostics
SPN 3031 DEF Tank Temperature Fault: Heater, Sensor, or Wiring
SPN 3031 points at DEF tank temperature strategy faults. Confirm heaters, sensor rationality, and harness chafe before replacing the tank assembly.
2026-08-27
Diagnostics
SPN 4094 Inducement Active: Meaning, Timers, and Safe Next Steps
SPN 4094 means inducement strategy is active, not that one part failed. Find the root emissions fault before the speed limit collapses.
2026-08-27
Emissions
When to Clean vs Replace an SCR Catalyst on Heavy-Duty Trucks
SCR catalysts fail from contamination and age, not every efficiency code. Use dosing proof and NOx delta before you buy a brick.
2026-08-27
Diagnostics
How to Force a Parked Regen With JPRO, INSITE, or DDDL
A forced parked regen only works when enable conditions are met. Use JPRO, Cummins INSITE, or Detroit DDDL to prove soot load, temps, and inhibitors first.
2026-08-19
Diagnostics
Intercooler Boot Leak Symptoms on Diesel Trucks (Before Turbo Replacement)
Whistle under boost, soft power on grades, and underboost codes often mean a charge-air boot leak—not a failed turbo. Smoke-test before you quote a turbo.
2026-08-19
Diagnostics
SPN 2791 EGR Valve Actuator Fault: Test Before You Replace Parts
SPN 2791 points at EGR valve/actuator control problems. Confirm command vs actual position, 5V reference, and carbon binding before condemning the cooler.
2026-08-19
Diagnostics
What Causes a Runaway Diesel Engine (and How to Stop It Safely)
A runaway diesel usually means the engine is burning oil or fuel it cannot shut off with the key. Kill airflow first, then find the oil or fuel path feeding it.
2026-08-19
Showing 13–24 of 119 articles