What does it mean when the J6P engine malfunction indicator light comes on?
2 Answers
The illumination of the GPR150 engine malfunction indicator light can occur during power-on self-test or under other circumstances. Power-on self-test is an indication that the vehicle is monitoring the status of all sensors before driving. Generally, if the engine is not started after power-on, the light will turn off by itself after about 3 seconds. In other cases, if the EPC indicator light comes on or remains illuminated for an extended period after the vehicle is started, the possible causes for the EPC light staying on include faults in the engine intake system, throttle valve issues, fuel system malfunctions, engine problems, ECU control unit failures, or brake light malfunctions.
I've been driving trucks for over a decade, and the most common reason for the J6P engine warning light is issues with the exhaust treatment system. A clogged urea pump or crystallized injector will trigger the light, especially in trucks using cheap urea from small manufacturers. Faulty exhaust temperature sensors or NOx sensors are also frequent culprits—the moment these sensors fail, the ECU immediately detects something wrong. If the diesel filter hasn't been changed for too long, abnormal fuel pressure can also trigger the warning. If there's no black smoke or loss of power, it's likely just dust in the sensor connectors or corroded plugs. Last time, I saw an old-timer ignore the light for three months until the exhaust pipe warped from overheating. That warning light is literally illuminated by blood and tears.
