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Catalytic Converter Repair ?

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So my car bombed on its emissions test during the MOT. The garage initially said they weren't sure if was the cat or a sensor. The fitter then came back and said it was both, in fact both sensors and the cat.

I'm getting a 2nd opinion from another garage as I'm dubious about the diagnosis of all three parts.

Worse still is the cat is part of the manifold and it's dealer only. On eBay VW Fox 1.4 cats are close to £300 used and £620 new from VW. The car's only done 44k and it's other wise a nice car.

I've seen a couple of repair places online but I've never been down this road before. I'm waiting for a quote or to even find out if it's repairable.

Thanks in advance.

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This can be a difficult thing to diagnose. In general, it's rare for a catalyst to fail on a modern car. However, if the emissions are off, then the car should have noticed, and turned on the engine fault light, and logged a diagnostic trouble code.

If a gas analyser has given a bad reading (as opposed to the MOT tester failing the car because the engine fault light is on) then it is likely to either be an engine running problem, the first sensor or the cat. The 2nd sensor's main role is to check that the cat is working correctly, and if not, turn on the engine fault light.

If the gas analyser has given a good reading, then it could be anything. When this happened to my car, it turned out to be a faulty wire to the 2nd sensor, but which happened to simulate a catalyst fault condition well enough for the ECU to misdiagnose it as a healthy sensor, but faulty catalyst. That was a time consuming and expensive diagnosis/repair, because some mechanics are taught that a 2nd sensor failure cannot cause a catalyst fault code.

I'd strongly suggest a 2nd opinion. It may be worth going to an independent garage offering Bosch diagnostics (Bosch being the electronics supplier to VW), as it was a friend-of-a-friend who does this type of work, who just sort of rolled his eyes at my tale, and said "Yup. Classic misdiagnosis. "

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If you do find it needs a cat find someone breaking one privately and ask them for the cat. I sell cats to a scrappy when I break cars (have 3 waiting in the garage for the next time I'm passing the place), no one wants to buy them privately. I had a 200CEL sports cat put in to the last SS exhaust I had built and it added £100 to the bill over a decat. Suspect the ones on ebay are chancers...

Cats can fail but its normally due to another issue, such as burning oil due to rings/seals.

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Probably running rich and the unburned fuel has choked everything. I would fix that then assess the health of the cat they can sometimes be ok with a bit of normal running. Upstream oxygen sensor is obviously the prime candidate but would have thought it would manifest in obviously poor running or a light on the dash. Something temperature related may cause over fueling without throwing a code with what appears like normal running.

The car's obviously low mileage but what's its actual age?

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Thanks again. Took the car which is 2006 btw,to another garage recommended by a friend who works in the trade.

I'm outside now waiting. However, it appears it was the top sensor only. He said it only just failed without the car being hot ie stone cold almost.

He's confident it will pass now with the new sensor. £50 plus his time. Mr Clutch wanted just under a grand.

I called Mr Clutch and told them. They said bring it back for a re test. I declined as I can't be bothered to mess around. Need the car and the mot runs out today.

Mr Clutch gave me a load of old bs on the phone. I'll complain in writing to head office.

Thanks again.

Edit to say it passed.

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