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Check Engine Light

So my exhaust system snapped right before the cat. converter and the check engine light went on (02 Sensor). I took it to the shop and they were able to successfully weld the it back on.

They cleared the code and told me that it had registered the code for 200 miles. I only saw the check engine light for 50 miles before bringing it to the shop.

Well now the check engine light is on again, I am pretty sure its the O2 sensor.

I was wondering if I needed to do one of a few things:

a) Since I have only driven 20 miles after the repair should I give it a few weeks and see if it goes away?

b) Replace the proper O2 sensor because the one I currently have has too much carbon deposited on it to give it a proper reading?


c) Go back to the shop so they can check their work since they might have missed a spot. (How likely is that?)

Vehicle 1999 Kia Sephia 130,000 miles.

First thing I would do is to read the code causing the light. The code should be in the format P1234. Come back and post the code.

I haven’t the time today to check the code and I intend on doing so but I am sure its the O2 sensor, not sure if its the up or downstream one.

“I haven’t the time today to check the code and I intend on doing so but I am sure its the O2 sensor”

never be too sure. It could be a wiring problem for example. A lot of people waste a lot of time and money, because the someone said the computer said it was the O? sensor only to find out it was the wire to the sensor or some like thing.

Lets get that actual code and see where to go from there.

I’ll be in St Louis for the coming week so I will get the codes and post. I wish I can get into a wager that its the O2 sensor setting off that CEL, mostly because after the welding, the code was checked and then cleared (it was the O2 sensor). I’ll get the exact problem code when I get back.

When the engine is cold, start the car, wrap a rag around your hand and press down hard on the opening of the exhaust pipe. If you can completely cut off the exhaust flow that way, there is probably a leak in the exhaust system – most likely at that weld. It takes a couple of minutes for the exhaust to warm up, so you won’t burn your hand. Still, use a little caution and common sense. I guess there is some risk that you might blow a hole in the system that way, but not in anything that wasn’t going to fail on its own in a few days or weeks.

And do read that code. Minor exhaust leaks don’t usually turn on the Check Engine Light on my vehicles.

GREAT!!! I will give that a try when I get back and keep you guys apprised of what happens when I do that and when I have that code.


The check engine light is typically for a circuit problem. Sometimes it is the sensor, other times it can be the wiring. Since the pipe broke, chances are there may be a problem with the wiring. Having the exact code helps, because there are several for each of the O2 sensors in this car. This will help narrow down the cause.

So I have some good news, it cleared up by itself!!

I’ll go and double check to make sure there are no stored codes. Thanks everyone!

Well the CEL is back on again the trouble code is P0422, anyone have any suggestions?

one of two or both, the rear or post cat o2 sensor is bad and needs replacing or your cat is bad and needs replacing. take it back to the shop, and let them test both. but don’t give them no ideals when you walk in, just tell that your light came back on, went out and back on and see what they say.

Thanks I will give that a try.

Give it one more day. Look for wiring damage at the rear sensor.