Did I get snookered over oxygen sensor?

I’ve been engaged in a two-month long saga with a new repair shop where it takes multiple visits, and hundreds of extra dollars, to get the car fixed properly. The latest problem involved the cause of the check engine light going on intermittently. When I first brought the car in for that problem, the garage said oh, when they worked on my transmission and gear box, they touched the oxygen sensor and didn’t put it back properly. So they put it back properly. Twenty minutes after leaving the garage, the check engine light went on again. I take the car back, and this time they say it’s the oxygen sensor, and charge me for the diagnosis/repair. I asked about it being related to the original oxygen sensor repair, and they said no, there are two sensors, and they screwed up the sensor in the back, near the exhaust, which they fixed previously. This is the oxygen sensor in the front, located near the top of the engine, and it’s just coincidence that it went on the fritz. So they are going to charge me for this repair.

Are there two oxygen sensors? And even if there are, shouldn’t they have made sure both worked when I brought the car in the first time for the check engine light problem?

What year car, model, engine? It all depends. Most newer cars have at least two. Some (like mine) have four. I think that many times oxygen sensors are replaced when the real problem is something else. The OBDII code never says that a particular part is bad. Instead it identifies an area of trouble, and then there is a troubleshooting process that should be run down. Many places don’t do this, instead they just throw what seems like the most likely part at it.

There may be anywhere from 1 to 4 O2 sensors but you have not told us what kind of car is involved.
As to what is going on here there is no way for any of us to know because we do not know what codes were set or anything else.

It could be possible for an O2 to be damaged during a transmission repair; especially if the transmission has to come out of the car but you have not told us much about this either.
Assuming this is a late model car with 2 O2 sensors (pre and post converter) it’s possible there could have been a misdiagnosis. It’s also possible if the exhaust was dropped out of the car to remove a transmision the banging and rattling could have caused an O2 problem.

All of that is strictly wild guessing though.

Touched the 02 sensor and didnt put it back in correctly. If you “touched” an 02 sensor you certainly could damage it if the touch was by a slipping wrench or a fall to the floor. A touch to a 02 sensor will not require it to be put back in these things are screwed in tight sometimes you cant even get them out. Doesn’t all add up

Thanks for the comments. To answer your questions, it is a '94 Mazda Protege with 199,785 miles on it. Sorry, I was rushing about and forgot that crucial info. I have no idea what the actual code was. The garage said the code indicated oxygen sensor problems.

Aww, the infamous Protege O2 sensor problem. I am currently on my second Protege and I have had this problem with both of them. It’s usually the front sensor and your shop should have known this. Just something that doesn’t seem to work right on these cars. I get the P0171 code for this. Check for exhaust leaks, as that could cause the O2 sensor to send a bad reading.