Hopefully you guys can suggest what happened. I had a local shop do an oil change and a small weld on the exhaust today on my 06 V8 4R. The two flanges connecting two exhaust pipes under the passenger's side floor pan were rusted to the point of separation and were loud.
The mechanic took the pipe off from the flange towards the driver's side and disconnected it at another flange that starts to go up towards the driver's side cat. He had to disconnect the lower O2 sensor during the repair.

After it was back together I drive way and notice the VSC trac, VSC and check engine lights are on. Definitely not on before. Turn around and he says I didn't notice them on then asks were they on before.

He read the code and says it the upper bank on the driver's side which he says he didn't go near. He reconnected the lower O2 sensor and cleaned it but it was still on.

Obviously there was something done by him during this repair to throw this code.

Any ideas?

Thanks

Was the code cleared via the OBD port after this? I don't think it will clear itself even if the malfunction causing the code is resolved.

I am not sure. I am going back today. He had a wireless scanner screen in his hand looking at the code so I'm assuming there was something plugged into the OBD port. He mumbled something about trying to clear the code.

it would be helpful to get the actual code number it is throwing vs being told " driver's side upstream" issue to start with.

From what I gather you're talking about the driver's side portion of the Y-pipe that starts down-stream of both of the cats and merges into the single exhaust collector, right?

Regardless, clearing the codes does nothing if the problem is still there. Once the system's initialize you'll get the light back on. I see a couple of scenarios of what could have happened ...maybe.. IF what he says about the code being for the upstream sensor is correct I don't see how that could be unless he also unplugged that sensor and possibly forgot to plug it in while first testing the exhaust when he finished up.

I guess it could also be possible that the sensor and or wiring were on the verge of going out and failed in the removal process. If I had to guess getting those exhaust bolts wasn't the easiest task and there was probably some impact wrench action happening... so it isn't out of the realm of possibilities that the sensor vibrated itself to death (not necessarily his fault if you ask me).

I have also seen catalytic converters meet their death during related exhaust fixes/removal with the same said vibration. I think your best bet is getting a clear code number to start with

The code is P0031 low bank 1 sensor 1

I looked it up and it appears to be the sensor up high before the cat.

The mechanic said it's throwing a code because there is a crack in the manifold. The crack has been there for a few years.

Thanks for sharing! Please report back when you find a solution

That's a code for the circuit voltage low... ie: failing/failed sensor. It should have nothing to do with the crack in the manifold. The upstream sensor is an Air fuel sensor. It doesn't monitor the efficiency of your exhaust system, but is there to adjust the air/fuel ratio mixture. If you had a significant leak above this sensor I could see it messing with some readings and possibly throwing a code, but P0031, best I can tell, has nothing to do with that..

you can check to narrow it down to see if it's a wiring issue (broken wire) or if the sensor is bad per the below:

"If the battery feed is intact, remove the ground (control) circuit from the ECM wiring connector and check for resistance on the circuit. If there is infinite resistance, repair open in the circuit. If the control circuit checks out, suspect a bad O2 sensor. Replace the sensor and re-check."



you could also do a mindless check as well... which would involve swapping the left and right sensors to see if the problem follows... but more than likely your sensor needs replacing (unless the previous repair damaged the wiring somewhere along the line).

good luck