Diagnostics
Common Causes of Check Engine Lights on Diesel Trucks
March 28, 2025 · 5 min read
On modern emissions-equipped diesels, the check engine light is almost always related to the aftertreatment, fuel, or sensor systems.
Top causes we see: DEF quality or level sensor, NOx sensor failure, DPF differential pressure sensor, EGR valve failure, leaking turbo boost line, MAP sensor, injector imbalance, and crank/cam sensor.
The fix is almost always cheaper than the consequence. A failed sensor that triggers a regen problem becomes a clogged DPF becomes an engine derate. Scan it as soon as the light comes on.