Help with engine light & O2 sensors please!

Technical Area Engine, Transmission, Exhaust etc
1
  1. My model of MX-5 is: __2002 Mk2 1.8l
  2. I’m based near: Bromley, Kent
  3. I’m looking for technical help or recommendations on: __Engine light / oxygen sensors / catalytic converter

Hi, this is my first post, just joined the club :slight_smile:
My MX5 is my pride and joy, I’ve had it a couple of years and am the first to admit I know nothing about it mechanically - I rely on my local garage to fix any problems.
BUT we have a problem at the moment that they just don’t seem able to pinpoint.
Briefly, the engine light came on, they plugged it into the computer and got the code P0420, so they replaced the top O2 sensor. They said to try the car but that the lower sensor may also need replacing.
After driving about 20 miles the engine light came on again - so it went back in and they replaced the lower sensor.
Sadly, having driven the car for about 50 miles over the weekend, the engine light has come on again!
Now the garage say it may need a new catalytic converter and to take it back in - but I feel like I’m just coughing up money for them to try different things and it’s not fixing the problem!
Does anyone have any experience of this happening - is it just a case of me taking it back to the garage and paying for a new catalytic converter - but then what if the light comes on again!!
I haven’t taken it back in yet - Any advice gratefully received.
Many thanks in advance
Sam

1 Like
2

I’m not an NB owner and never have been, but enter “P0420 fault code” in the search bar of this forum. There are numerous threads on this issue which may be of help.

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So is that the only code she is throwing out? sometimes you can get other codes that might direct you to why that code is showing…

First options are to the cat and O2 sensors …
Is there a rotten egg smell? or sulfur smell which is a massive kive away that the cat is dead?

But There are a number of other things that could be directing the issue…

  • Exhaust leak
  • O2 sensor wiring
  • PCM issue
  • Overheating converter (usually caused by a misfiring engine, there should be codes)
  • Burning oil (overheats converter, usually no code)
  • Engine not heating up enough
    M-m
4

This is the problem with using people who are unfamiliar with these vehicles and don’t understand the process of fault finding.
To see exactly what the problem is you need to be able to scan the data from both sensors which will tell you which one if any is faulty. Then you can see what the difference is between each sensor. If they both read the same then its almost certainly the cat thats the problem having eliminated any of the other causes that MM has mentioned.

5

Thank you, lots of help on here

6

Thank you so much, I’ll investigate - there’s definitely no sulphur smell so hopefully that’s good news!!

7

Thank you - I really need to find a specialist mechanic or garage local to me who knows these cars specifically