Engine management light showing

  1. My model of MX-5 is: __series 2 year 2004
  2. I’m based near: __stourbridge
  3. I’m looking for technical help or recommendations on: __engine light keeps coming on dash, after having a new catalytic converter fitted, after the old was stolen. Keep taking it back to the garage and fine for about 3 days and then comes back on. Has anyone else had a problem or any ideas what could be causing it. Garage seems to think it’s the sensors but still can’t find the fault- thanks

What’s the code that it stores? Catalyst efficiency below threshold?

Thank you for responding.
I don’t know the answer to your question, just keep taking it back to the garage, who are trying to fix it. However, I will ask the question. They have changed the front sensor, thinking the sensors could be the problem. Having rang the garage this morning to let them know the light has come on again, after only having it back for 2 days, using it on one short journey and one good blast down the dual carriage. I have to take it back and they will change the back sensor. and see if that eliminates the problem

Just wondered if anyone has had the same problem when replacing the CC after original one stolen

Thanks you again


As Robbie says, important to know what error is occurring. There will be at least one error code stored if the engine light comes on and the garage should be able to let you know what that is.
Having recently changed the cat it would seem likely that the issue is related but very unusual for a new catalytic converter, properly commissioned to cause issue. If the error is Catalytic converter efficiency as seems likely, the cat or lambda sensors are to blame. Catalytic efficiency is checked by comparison of readings from the two sensors, so they are all potentially the cause.
Assuming the error relates to Catalytic efficiency…
If the lambda sensors were simply refitted, there should not be a problem unless they were damaged when handled or there has been a subsequent wiring/connector issue. Who manufactured the replacement cat?

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HI Rob

Thank you for your reply much appreciated.

I have just collected my car back from the garage again, with the management light still on.
I did asked the question, which Robbie asked me and read out your additional response. However all I got back was we have ordered a new sensor, should take a few days. so I am in their hands.

I will let you know the outcome when the new sensor is fitted.

Once again my thanks to you and Robbie for you responses.



You are never in a garage’s hands buddy, take some control.
Buy yourself an MS309 error code reader off ebay and take a more proactive approach…
MS309 OBDII Scanner Check Engine Fault Code Reader | eBay
This device will allow you simply to interrogate any OBDII car’s stored error codes.
Your garage do not appear to be doing too well with this issue.

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+1 for the MS309. I bought one on Rob’s recommendation. It’s a very useful tool to have. Interrogate the error code, and you will have a good idea what needs to be done / fixed.

Hi Robbie

I took my car to the garage where I would normally go, and had a pre MOT, and it failed on emissions. (There’s a surprise)

Fast Idle Test
CO 0.46 % Vol
HC 214 ppm
Lambda 1.02

2nd Fast Idle Test
CO 0.63 %Vol
HC 71 ppm
Lambda 1.01
The summary results:
Fast idle Test Fail
CO 0.20 Fail
HC 200 Fail
Lamb 0.97-1.03 pass

2nd Fast Idle Test Fail
CO 0.20 Fail
HC 200 pass
Lamb 0.97-1.03 pass

Idle Speed Fail
CO 0.30 Fail

Exhaust Emissions Test Overall Result Failed

Therefore, I presume, the garage, currently working on my car, hadn’t done this check as I did inform them I was taking it in for an MOT.

The Cat was obviously an aftermarket one, and I was told by my garage, it looked like it hadn’t been fitted properly and the cat, in his opinion, was not the correct one.

I will be ringing the garage on Monday for an explanation and give him the opportunity to rectify the problem, or I will be informing the Insurance Company, and asking the question as to why they are the Insurers approved garage.

Thanks again for responses


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