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Tune-up Check Engine Light

I finally got around to getting a tune-up for my Chevy Cavalier a few weeks ago. It has around 125,000 miles on it. The mechanic changed the spark plugs, fuel filter, and air filter.

The day after, it idled extremely rough and had almost no accelleration. I barely made it home from work. The next day it wouldn’t start and I had it towed to the shop. The shop fixed a wire that had come loose from the engine.

The next day, the check engine light came on. The mechanic said it was the O2 sensor and there were some misfires. He thought it was just residual from the first problem and resent the light.

The next day, it came on again with the O2 sensor. He replaced the fuel filter again.

A day later, it came on again. He changed the O2 sensor this time.

It came on once again. I think this time he tried a new set of spark plugs.

This morning it came on again. What could the problem be?

There is no way that anyone can tell you what the problem could be without knowing the error codes stored in the computer. The format is P1234. Your mechanic may have written them on the invoice or might be able to tell you what they were. Alternatively you can have the codes read for free at big chain auto parts stores.

If the check engine light blinks don’t drive the car.

If the car started running very rough only after the tune up the first thing off the top of my head would be defective/bad spark plug wires.

The running rough was fixed when I had it towed to the shop. It was that the wires to the engine had come loose. Since that was fixed, it has been running fine, just the check engine light keeps coming on.

The mechanic didn’t tell me the exact code, but he said it was the O2 sensor.

You need the exact code. “It’s an O2 sensor” is one of the most commonly heard things - but ironically, its almost never the O2 sensor. So if you want some help, get the exact code.

I called the mechanic. He said that after the O2 sensor was changed, it is now pointing to the Cat Converter with a code of P0420.

I have a feeling that the car was running on 3 or 5 cylinders. You dont tell us year, model, or engine size.
In doing that, it dumped a lot of unburned fuel into the exhaust, because you decided to drive it home instead of getting it towed even though it was almost not running.
The O2 sensor probably got all gunked up and the cat converter probably burnt up because it couldn’t handle all of the fuel going through it.

Thanks for your reply. It’s a 2003 Chevy Cavalier 2.2L 4-cyl.