Check Engine Light Comes on and Off

An intermittent check engine light is trickier than one that stays on. It means the problem comes and goes, which makes it harder to catch — but it's still real.

When your check engine light comes on and off, the engine computer is detecting a problem intermittently. The condition triggers the light, then resolves itself temporarily, and the computer turns the light off after a certain number of clean drive cycles. Common causes include a loose gas cap that seals sometimes but not others, an intermittent misfire, a failing oxygen sensor that works at some temperatures but not others, and loose wiring connections that make and break contact with vibration.

Even though the light goes off, the trouble code typically remains stored in the computer's memory as a "pending" or "history" code. A professional scan tool can read these stored codes even when the light isn't currently on. This is key — you don't have to wait for the light to be on to get it diagnosed. The stored codes tell the mechanic exactly what condition was detected, even if it's not happening at that moment.

Ez Mobile Mechanic reads both active and stored codes to diagnose intermittent check engine lights throughout Jacksonville. As a mobile mechanic in Jacksonville, we come to your location with scan tools that read pending and history codes, so we can catch the problem even when the light is off. No tow truck needed. Call (904) 788-7272 before a sometimes-problem becomes an always-problem.