DPF, SCR & AftertreatmentRepair in San Diego
Derate codes, failed regens, and aftertreatment faults are the #1 reason trucks come to LTEK. We specialize in DPF, DOC, SCR, DEF, EGR, and NOx sensor diagnostics and repair at our Otay Mesa shop in San Diego.
We don't just clear codes — we trace every derate condition to the root cause using ECM live data, then fix it so it doesn't come back. Derate recovery is our specialty.
Understanding Your Truck'sEmissions System
Every modern diesel truck uses a multi-stage exhaust system to reduce emissions. When any stage fails, you get derate codes, power loss, and eventually a forced shutdown. Here's how the system flows.
Diesel Particulate Filter
The DPF traps soot particles from exhaust. Over time, it fills up and needs to regenerate (burn off soot at high temperatures). When regen fails — due to short trips, sensor faults, or engine issues — soot builds up and triggers a derate. We diagnose whether the DPF needs cleaning, a forced regen, sensor replacement, or a new unit.
Selective Catalytic Reduction
The SCR uses DEF (urea) to convert harmful NOx gases into nitrogen and water. When the SCR catalyst degrades, NOx sensors detect inefficiency and trigger derates. We test SCR conversion efficiency, NOx sensor accuracy, and DEF dosing rates to pinpoint the failure — not just swap sensors hoping for the best.
DEF Dosing System
The DEF system includes a pump, injector, tank heater, quality sensor, and dosing valve. Any component failure triggers a derate countdown — typically 5 mph speed reduction followed by engine shutdown. We diagnose which component is failing and replace only what's needed.
EGR Valve & Cooler
The EGR recirculates a portion of exhaust gas back into the engine to reduce combustion temperatures and NOx. Carbon buildup clogs the valve; cooler leaks contaminate coolant with soot. We clean or replace EGR valves and diagnose cooler failures before they become head gasket problems.
Derate Issues We Fix Every Day
Power Derate / Speed Derate
Truck limited to 5 mph or 25% power? Usually aftertreatment-related. We identify whether it's DPF soot loading, SCR efficiency, DEF quality, or sensor faults causing the derate condition.
Failed Regen / High Soot
Regen won't complete? Could be exhaust temp sensors, DPF pressure differential, injector 7 (doser) failure, or an upstream engine issue preventing proper regen conditions.
DEF System Faults
DEF quality warnings, pump failures, frozen tank heaters, and clogged injectors. The derate countdown starts immediately — we diagnose and repair before you run out of time.
NOx Sensor Failures
Inlet and outlet NOx sensors monitor SCR efficiency. When they fail or read incorrectly, the ECM thinks the SCR isn't working and triggers a derate. We test actual conversion efficiency before replacing sensors.
EGR Valve & Cooler Issues
Stuck EGR valve, carbon buildup, and EGR cooler leaks. Coolant contamination from a leaking EGR cooler can destroy engines if not caught early.
CARB Clean Truck Check Failures
Failed the CARB Clean Truck Check? Aftertreatment issues are the most common cause. We diagnose the failure, perform required repairs, and retest on-site with CARB-approved equipment.
Common Questions
How much does DPF repair cost in San Diego?+
DPF repair costs depend on whether it needs cleaning, sensor replacement, or a full unit replacement. Call us at (619) 848-0459 for a diagnostic — we'll identify the exact issue and provide an accurate estimate before any work begins.
Can a DPF be cleaned instead of replaced?+
In many cases, yes. If soot loading is the issue and the filter substrate isn't damaged, a professional DPF cleaning can restore it to near-original flow. We'll assess the filter condition and recommend the most cost-effective option.
Why does my truck keep going into derate?+
Recurring derates usually mean the root cause wasn't fixed — just the symptom. Clearing codes without fixing the underlying issue guarantees the derate will return. We trace every derate condition to the actual failed component using live ECM data.
What's the difference between DPF and SCR?+
The DPF captures soot particles from the exhaust and burns them off during regeneration. The SCR uses DEF (urea) to chemically convert NOx emissions into harmless nitrogen and water. Both systems work together — a failure in either one can trigger a derate.
Do you handle CARB Clean Truck Check failures?+
Yes. Most Clean Truck Check failures are aftertreatment-related. We diagnose the specific failure, perform the required repairs, and retest your truck on-site using CARB-approved testing equipment.
Can you fix my DEF system before the shutdown timer runs out?+
We prioritize derate and DEF system repairs because the countdown timer is real — once it hits zero, your truck shuts down to 5 mph. Call us immediately if you're on a DEF countdown. We'll get you in fast.
