Engine Management Light

Either that or just use a small strip of black sticky tape.

Actually, you probably didn't fix the original problem, just reset the fault timer to zero. After some time the number of faults read by the computer will once again trip the light.

Some component is failing or at the hairy edge of of its operating limits and each time it goes outside that limit it will log a fault. When enough faults are captured it will trip the display light. This is how Ford (and others) prevent false positives.

It could be the EGR valve or the sensor that is the real problem.

You're right, though I wasn't kidding myself I'd fixed the original problem. But getting rid of the light is a plus, and it's a reasonable bet it's the same problem recurring, not something more serious. Must change that EGR valve!

It's a good idea to have the EGR working properly as it effects other systems as well...

http://www.allfordmustangs.com/forums/2-3l-tech/233592-egr-valve-disconnect-not-disconnect-myths-fables.html

Thanks. Interesting. I must bite the bullet and change that valve!

automotive computer systems are very complex, even having the computer read and the so called problem known, doesn't mean that is the problem. I had a lean burn error on my car, which according to the manual means a vacuum leak, but the problem was an O2 sensor. Just because it may have been the EGR valve the last two times, it may not be the third, maybe the MAF sensor is dirty. A loose gas cap can cause an error code. trying to fix a check engine light without an error code checker is like trying to answer a posting on CR4 without a monitor. In America code readers are about $50-$60, less that what a mechanic charges to pull the code, and then you need a manual to interpret the code. I change O2 sensors every 2-3 years, It can make quite a difference on fuel economy

You can actually "fix" a lot of modern (generally computer controlled) equipment in this way.

I have fixed calculators, clocks, washing machines, dryers, GPS Systems and just last week, my old digital camera....

What I believe happens (observed over many years, but not in any way "proved"!), is one of three things (but could be more, let me know what you think):-

1) Device firmware has entered a condition that was not foreseen by the programmer and is basically "stuck" in a branch to "nowhere".....a firmware update may fix this problem forever. Not always possible....

2) Probably the batteries went below a certain voltage level and "brown-out" situations were not foreseen by the programmer and the firmware went into a similar condition as 1).

3) An electrostatic discharge has happened to the equipment by someone with a high charge on their body touching it, which has "freaked out" the firmware in some manner. There may even be permanent damage to delicate components....the device was badly designed from new probably....

The usual way to get the problem fixed is similar to the way you fixed your car. That is remove battery/mains power completely, press all buttons and switches on the device, short out the battery connections, leave it for 24 hours with no power or batteries.

Though some devices may need longer I have found, my camera and some calculators for example....

After the time is up, use fresh batteries in battery equipment and see what happens.

I have posted about this problem/fix here on CR4 some years ago....it is fairly well known.....

Best of luck.

Another possibility is that the firmware has been hard-coded to throw up faults so that you have to take it it to get it diagnosed! If the product is to reliable, how can they make money? (No, I'm not pessimistic..., just a little sarcastic).

That has probably happened from time to time, but it only needs for that to be found out by someone like the people on Tom's Hardware and that company's finances could take a nose dive....

Its a possible way to harm your bottom line forever....if found out!

Using the method I wrote about will not always work in bringing something back to life, but cheap and easy to try out....

Making dangerous firmware problems I liken it to the Basic POKE command for a commodore Pet many years ago that could burn the CRT power supply!!! DUUHHHH!

See here:-

Commodore Pet Killer Poke

So it has happened on at least one machine type as you mentioned....

Black electrical tape placed in an area that stops the light from being seen from drivers seat.