Semi-Truck Repair Guide
Structured repair guidance for Freightliner, Kenworth, Peterbilt, Volvo, Mack, and International trucks. Know the most common failures, how to diagnose them, and how to fix them right.
Common Semi-Truck Failures
Aftertreatment System Failures
DPF clogging, SCR catalyst degradation, DEF injector failure, and NOx sensor faults are the most common semi-truck breakdowns. Most trigger derates that reduce power to 5 mph if not addressed.
Turbocharger Failures
VGT actuator failure, oil starvation, and compressor wheel damage. Symptoms include low boost, black smoke, and turbo-related fault codes (SPN 641, 1127, 102).
EGR System Failures
EGR cooler leaks, EGR valve sticking, and EGR differential pressure sensor faults. Causes rough idle, white smoke, and coolant loss.
Fuel System Failures
High-pressure pump wear, injector failure, and fuel filter restriction. Symptoms include hard start, low power, and fuel rail pressure fault codes.
Electrical & Sensor Failures
Crankshaft/camshaft position sensor faults, NOx sensor failures, and wiring harness damage from heat and vibration. Often causes no-start or intermittent stalling.
Cooling System Failures
Water pump failure, thermostat failure, and EGR cooler leaks. Overheating causes severe engine damage if not caught early.
Step-by-Step Repair Logic
Use the sensor locations guide to find components on your platform, cross-reference common truck problems for symptom-based starting points, and verify fastener specs in the torque specs reference before finalizing any repair.
- 1
Connect a scan tool
Pull all active and pending fault codes. Note any active derates — they tell you how urgent the repair is.
- 2
Review live data
Check DPF soot load, DEF level, boost pressure, fuel rail pressure, and coolant temp. Abnormal values narrow the diagnosis.
- 3
Inspect the obvious first
Check fluid levels, inspect for leaks, look for damaged wiring or connectors. Many failures are visible before testing.
- 4
Test — don't guess
Use a multimeter and scan tool to confirm component failure before ordering parts. Parts cannon repairs waste time and money.
- 5
Fix root cause
Understand why the component failed. A failed NOx sensor may be caused by contaminated DEF. Fix the cause, not just the symptom.
- 6
Verify the repair
Clear codes, perform a test drive, and confirm the fault does not return. Check live data to confirm values are back in spec.
Supported Platforms
| OEM | Engines | Common Issues |
|---|---|---|
| Freightliner | Detroit DD13, DD15, DD16 | Common: EGR cooler, DPF delta-P sensor, NOx sensor |
| Kenworth | PACCAR MX-11, MX-13 | Common: VGT actuator, DEF injector, fuel rail sensor |
| Peterbilt | PACCAR MX-11, MX-13 | Common: VGT actuator, DEF injector, fuel rail sensor |
| Volvo | Volvo D11, D13, D16 | Common: EGR valve, DPF, NOx sensor |
| Mack | Mack MP7, MP8, MP10 | Common: EGR cooler, DPF, turbo actuator |
| International | Cummins ISX, X15; Maxxforce (legacy) | Common: EGR, fuel system, turbo |
| Western Star | Detroit DD13, DD15, DD16 | Common: Same as Freightliner DD-series |
Ready to diagnose your truck?
Run a full guided diagnosis or ask Technician Chat for platform-specific help.