Troubleshooting guides

The problems owners and techs discuss most, with checks ordered cheapest first.

• DEF / SCR derate: how to find the real causeAftertreatment / SCR
• NOx sensor failures: confirm before you replaceAftertreatment / SCR
• DPF won't regen or keeps regenerating: a practical checklistAftertreatment / DPF
• Losing coolant with no visible leak? Check the EGR coolerEGR / Cooling
• Low boost and limp mode: VGT actuator and turbo troubleshootingAir intake / Turbo