Check engine light diagnosis

A check engine light stores a code, and a code names the circuit that is unhappy. It does not name the part. Those are two different things and the gap between them is money.

• A free code read at a parts counter names a circuit, not a part
• A flashing light means stop driving, a steady one means book it
• Joe reads live data, not only the stored code
• You get told what it is before anything gets bought

A parts store will read the code for nothing, and that is a fair deal for what it is. What you get back is a circuit. A code that points at an oxygen sensor can be caused by a bad sensor, an exhaust leak ahead of it, a vacuum leak or a failing fuel pump.

Buying the sensor is a coin flip. Joe reads the live data while the engine runs, which is the part that separates a guess from an answer.

A light that flashes rather than glows is the one to take seriously today. That is a misfire dumping raw fuel into the exhaust, and driving it turns a cheap coil into an expensive catalytic converter.

A steady light is not an emergency. It is a booking. Send a photo of the dash and the code if you have it, and Joe will tell you whether it is a tonight problem or a Thursday problem.