Engine check light fades

[-Jc.]

Anyone seen anything like this before?

The yellow engine check light comes on at startup, stays for a while, then FADES gently as the engine warms up. Colder the day, longer it stays.

Beat's running absolutely as normal, no funny noises, leaks, smells, misfires etc. No history of problems. Engine rebuilt seven years and 25,000Km ago after cambelt supernova.

I've searched around for similar symptoms, but it seems that usually the light is either on or off, not somewhere between.

I spoke to the local garage where I get the servicing and they're not worried, although they've never seen one fade before.

I'm puzzled. Any ideas?

[Wh1teLeopard]

I'd check for a fault code.

You need to use the yellow connector in the engine bay and see if a code flashes up.

If you're not sure how to do this:
http://u-ukhbc.co.uk/vbb/showthread.php?t=1448

Should help :)

[Oktan]

I've never heard of a fading CEL before, sounds like a bad lamp driver in the ECU. If you can source another ECU locally you can try swapping them. Otherwise I have one laying around but I'm in Denmark. Could send it of course :-)

[-Jc.]

Finally plucked up the courage to get my hands dirty. Eventually found it hidden away wrapped in blue tape (thanks previous owners!).

And guess what? No beeps, flashes or other magic. The yellow engine check light remained on at full brightness. Without the jumper connected, it stays bright for the usual couple of seconds, then dims a bit. Reset the ECU - no change. Light still fades away as the engine warms up.

Stumped again. If anybody has a spare ECU (maybe closer, thanks Oktan!), I'd be happy to try it out.

[-Jc.]

Although the light still comes on and then fades, I discovered today that it goes off instantly if I turn on the a/c! Work that one out?

It took me this long to find that out because the air con hasn't worked for ages (having discovered that the conversion's expensive and then done the recharge with illegal gas "shh! go round the back and ask for Dave" -cool air for about a week, now given up)

So there you go. If your engine check light comes on -don't get a repair, just turn on the air!