Mechanic work might have borked a sensor

Markc0011

Hello,
So I bought a used car for £1000, I had it serviced (£200)
Then 2 months later I had exhaust problems, and as I immediately needed it doing, I went to a different garage than my usual, as my usual was shut on Saturday.
So this other garage said, 'I think we've fixed it but your catalyst convertor is looking rusty, want to replace that?, and that will be £200.
So on the spot, I said 'yes'.
Little known to this different garage that I had a MOT coming up the following week which I did at my usual garage.

Problem- MOT comes up with a new advisory - 'exhaust minor leak of exhaust gases(joint from cat to exhaust), and also a ball bearing(fixed).
I didn't know what to do re: what was clearly showing a fault of the other garage's work. And to make it worse, my usual garage right next to this other garage, seemed to cover up for the other garage saying 'it will seal over time'.

Two weeks later, my engine management light comes on. I go over to my usual, and they now say its a Lambda sensor. And it will be £150 to repair. I am not 100% convinced considering the advisory, so I take the bill as it is (which is £42 for diagnostics), and go away without the sensor being repaired. My idea being to get a 3rd garage to look at it.

So all this my car was fine to begin with, I agree to get a catalystic convertor and somehow gain a new advisory, my lambda sensor is possibly now borked with a new £150 costs and also now a small trust issue with my usual garage.

I'm being told I should go back to the other garage over their workmanship but I can't see them replacing a £150 sensor if they borked it. What advice is there from here?
Thanks.

facade

Take it back to the first garage and get them to fix the leak and have a look at why the engine management came on right after they replaced the catalyst.

The second garage are correct- a very minor leak at a joint will usually fix itself over time as it corrodes and soots up.  Certainly they wouldn't fix it for free, and you are better going back to the garage that fitted it if you want it fixed now.

The engine light could actually be caused by the exhaust leak, the sensor could have chosen to fail deliberately at a time that makes you think it was something the garage did, or they may have damaged it or its connector when they swapped it over to the new catalyst.

Next time, resist any upsells, especially with an MOT due, unless they state categorically that it will definitely fail without the upsell.