Best of Deals Car Reviews Repair Shops Cars A-Z Radio Show

Engine light

engine light on - computer says slightly lean fuel mix. loose battery cable tightened, engine light out. few weeks engine light on. same a month later. now engine light on need smog check - any ideas why light on and how to turn off. been driving with light on 6K - car very good.

Year, Make, model, mileage, diagnostic trouble codes please. There is no such thing as a “slightly lean” code.

The code is like P12345, go to any parts store like Autozone and if you ask they will read it for free. Post the code here and people can help more


You need to have the code read and post it for us. We’ll give you advice

Don’t automatically assume the light is back on, with the same code. Might very well be a different code this time :neutral:

If the battery was ever disconnected at some point (like when your shop tightened the connections), that itself could turn off the check engine light. Then it will automatically turn back on a few days later, for the same reason it turned on in the first place. Removing the power resets the computer memory, and it takes some driving time for it to figure out what should be in that memory after re-powering. Once it figures out what’s in the memory, then it discovers there’s a problem again and turns on the engine light. That’s normal behavior for modern engine computers.

A lean mixture code means there’s too much O2 in the exhaust stream, and the engine computer is having to add more fuel to balance that extra O2 out than it thinks it should have too. There’s a test called “fuel trim” that could help your shop get to the bottom of the cause. Could be something as simple as a cracked vacuum hose. That’s like a $35 fix, parts and labor. Of course it could be something a good deal more expensive too. That’s why you need further testing.

BTW, if you now have now developed an idea that you can disconnect the battery to turn off the engine light so you can get you smog check, that won’t work. Put that idea to bed. The emissions folks know all about that trick and how to put the kibosh on it.