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post #5 of (permalink) Old 2nd July 2007 Thread Starter
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Hi Chris and everyone. Well, you were correct in your diagnosis of the lambda sensor. I took the car into a garage on recommendation and they put it up on the ramp only to find that the sensor was actually unplugged! They were slightly aghast, as was I. Part of the exhaust was replaced pre-MOT in April and then, when it failed on emissions, the garage replaced the catalytic convertor. Nothing has been done to it since. I took a photo to prove it to the other garage. Thank God for decent camera-phones!

The garage I took it to today said 1) it is normal, good practice to replace the lambda sensor when replacing the catalytic convertor, 2) it is possible that a faulty lambda sensor could have resulted in a damaged cat and this could have been the very reason for that to have needed replacing in the first place and 3) the fact that it appears the car has been running for two months without the sensor attached could mean that the new cat could now be damaged. They told me that it is not possible for the lambda sensor to become detached in the normal course of driving, as it is a snap-fit thing and can't just fall out, and that it would have had to have been detached to replace the catalytic convertor and must have simply not been re-attached afterwards.

I spoke to the garage who replaced the cat this afternoon and they have said they will look at it tomorrow for me. They said that they do not routinely replace the lambda sensor when they replace a cat and only change it "if required". They didn't elaborate on how you determine whether it is required or not. They did admit that it is possible that the sensor may not have been re-attached after the cat was replaced.

As I know next to nothing about any of this I would very much appreciate anyone's views on any of this. Particularly,
  • what test is there that would show that the lambda sensor does or does not need replacement separately to the catalytic convertor?
  • As the sensor is nearer the front of the car I presume that the rear-ender I had would be unlikely to have anything to do with this or would it be possible for the accident to have damaged the plug of the sensor so that it can detach itself?
  • The garage I took it to today who noticed the detached sensor plugged it back in for me (so they said) but now the engine management light is back on, so is it now likely to be lit because of a fault in the sensor or could it have become detached again?. It is right underneath the car so I can't easily check.

Thanks for any help or advice you can give me. I do love this car, having had it since it was born , but I am now beginning to wish I had cut my losses when it failed the MOT!
Currently in suey's garage:
1997 Scenic 2.0 auto
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