On a modern diesel the exhaust isn't just pipes — it's an emissions system with a filter, sensors and a chemical dosing setup. When it acts up it doesn't just get loud; it derates the truck.
Exhaust leaks still matter
A cracked manifold, a blown gasket or a leaking pipe upstream of the sensors doesn't just make noise — it skews the readings the ECM relies on, which can trigger faults and hurt performance. On today's trucks, a plain exhaust leak can become an emissions problem.
DPF and regen
The diesel particulate filter traps soot and burns it off during a regen. Lots of short trips, idling, or a sensor fault can leave it unable to regen, and it plugs. A plugged DPF chokes the engine and forces a derate. Sometimes a forced regen and cleaning restores it; a filter that's been abused or oil-contaminated needs service or replacement.
DEF-system faults
- Poor DEF quality or contamination throwing codes
- Dosing / injector and pump faults
- NOx or temperature sensor failures
- Any of which can put the truck into a countdown derate
What we do
We diagnose the whole path — exhaust integrity, DPF condition, regen behavior, and the DEF/SCR system — using codes and live data. We repair leaks, clean or replace the DPF as needed, and fix DEF dosing and sensor faults, then verify a complete regen so the derate stays gone. Keeping the system honest is also what passes a CARB Clean Truck Check.
Need exhaust & emissions repair? Long Road Repair handles it in-shop and mobile across the South Puget Sound. See our exhaust & emissions repair service or call and talk to a real tech.
FAQ
Why does a clogged DPF cause a power derate?
A plugged filter restricts exhaust flow and the ECM cuts power to protect the engine and force service. A forced regen and cleaning can restore a salvageable filter; a badly abused one needs replacement.
Can an exhaust leak cause check-engine lights?
Yes. A leak upstream of the sensors skews their readings and can trigger emissions faults and poor performance. On modern trucks, exhaust and emissions are one system.
What causes DEF system faults?
Poor DEF quality or contamination, dosing/injector and pump problems, or failed NOx and temperature sensors. Any of these can trigger a derate countdown — we find the specific cause.
Will fixing these help me pass emissions testing?
Yes — a healthy, fault-free exhaust and aftertreatment system is exactly what's needed to pass CARB Clean Truck Check and stay legal.
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