Hi everyone,

I’m stressed right now because my car just failed its MOT due to high emissions. The garage said it could be the catalytic converter or the exhaust system, but they’re quoting a huge amount for repairs. Has anyone else dealt with this before?

I’m wondering if there’s a cheaper fix or if I should get a second opinion. Also, I’ve heard that using fuel additives or giving the car a good run before the test can help—does that work? I’m on a tight budget, so I’m trying to figure out the best way forward without breaking the bank.

Any advice or experiences you can share would be a massive help.

 

thanks in advance for any help

 

What did it fail for? Hydrocarbons, NOx, CO? Not really enough information to give a solid answer, could be hundreds of things.

 

Try a bottle of Cat-a-clean or another form of additive. Might be enough to pass. Here in the states mine failed and I ran a bottle of fuel system cleaner and it passed on the second try.

 

It sounds to me like the mechanic you’re dealing with is just guessing. It might not be difficult or expensive to fix. Guessing at a bad Cat sounds really suspect to me.

 

Does your car have any codes?

A leaky exhaust will destroy the cats quickly, it’s probably both.

 

You don't say what specific diagnostic code(s) was/were present, but the fact that you say your garage said the cause could be the catalytic converter indicates the fault code is either P0420 (Bank 1, left-hand side as viewed from the driver position) or P0430 (the other side).

The fault does indicate a failed catalytic converter, but it could also be a failed oxygen (O2) sensor. The fault is unlikely to appear on both sides at the same time. A sensible diagnostic next step is to swap the O2 sensors from one side to the other. If the fault codes "move" to the other side that would indicate a faulty O2 sensor. If the fault code stays on the same side a failed catalytic converter is indicated. If that's the case, trying one of the quick fixes suggested here by others is a relatively low cost alternative to replacing a catalytic converter.

You don't say where you are located, but your use of the term MOT indicates you may not be in the United States. If you share your location you may find there is a forum member nearby who can help with getting diagnostic codes read.