Check Engine Light

[crazyLex'96]

My check engine light use to come on and then go off. But now it has been staying on and my friend which is a mechanic say's nothing is wrong with it after inspecting it and he unhooked the battery to reprogram it. And it stayed off that entire day, but in the morning when i went outside to warm up my car it came back on so i did the whole battery thing again and it stayed off entire day again, but the next day when i went to warm up my car it was on again, so it only turns on when engine is cold i dont understand why though. If anyone know what could be wrong let me know please

[steviej]

don't just erase/clear the check engine light. Get the codes read. Autozone will do it for free. A lexus dealer may charge you a diagnostic fee of around $80. You may have to have it read when the engine is cold and the code first appears. This may involve leaving the car at the dealer overnight so he gets the trouble code upon cold start up. Or start it up, get the code, don't clear it, drive over, read it. It is that simple.

Did you mechanic friend hook up a scan tool to read the code?

If he didn't then how does he know "nothing is wrong with it after inspecting it"?

Bottom line, the check engine light is coming on due to a trouble code. Identify the code and you will find out what the car is telling you.

It may be as simple as the gas cap needs replacing or an O2 sensor is bad (my guess because it is cold activated but not hot).

It may be and intake air temperature sensor, it may be a cold start up sensor, etc.

You won't know until the code(s) stored in memory or the code tripping the light is identified. That is why the light is there.

good luck and post your findings.

steviej