Ford Mondeo III (2000 - 2007) - 01 1.8 Do Engine Warning Lights Get Bored?

Honest John Back Room » Technical matters
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Thu 10 Dec 2009 20:07
01 1.8 Do Engine Warning Lights Get Bored? - beany75
I had an engine warning light come on several months back - steady light rather than the PULL OVER light. Took it in and it was diagnosed as a faulty EGR valve.

Being tight I bought a second-hand unit off of ebay for about £12, fitted it and everything seemed to be fine. About a month later the light came back.

Now not only am I tight but I'm also lazy. To be honest I don't like working on cars, my hands always come out from under the bonnet with less skin on them. Anyway, the EGR valve I'd put in would probably have benefited from a clean and I put the light coming back on as being the valve sticking. The car still drove normally.

As what I thought might be proof, I disconnected the battery to reset the light and looked to see how many miles I could go before it came back. I figured if the valve didn't work at all it would be back in a few miles. It was over 1000 miles before it came back so I felt happy with my diagnosis. I assumed that the valve probably stuck some days and worked others but once the light was triggered it would stay on until someone reset it again. I realised that with the light permanently on I wouldn't know about any other faults but hey.

So finally...

Several months down the line the light went off by it's own accord (no the bulb didn't blow). So what does this mean? The ECU is ignoring it based on some sort of time elapsed function or the fault has gone for long enough for it to decide to stop reporting it?
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