2004 E320 no CEL- I found out why, and you won't believe it
 

I have been trying to get my 2004 E320 wagon to pass smog. I first took it in, and the tech told me it has no CEL. I only bought the car a few days ago, I didn't notice it being out (I am a Diesel guy, and didn't even look for it). I have another car (sedan), so I pulled the cluster out and swapped it. The CEL worked, but the odometer showed - - - - - - -. No problem, it only needed the CEL to work. Back to the smog station, it now has two IM monitors that won't set. I started this ththread: http://www.peachparts.com/shopforum/tech-help/394453-2004-e320-drive-cycle-secondary-air-monitor-not-ready.html
Now, I decided to try and find out how to replace the CEL bulb in the wagon cluster. I disassembled the cluster and removed the circuit board with the clock in it. Much to my surprise, there are no replaceable bulbs, but LED's. I then looked through the window where the CEL should be, and it was all black with no "check engine" shining through. I pulled the circuit board off the other one (sedan), and I could clearly see the check engine through the window. I thought: how could this be? It has to have a CEL! I got a flashlight and looked down inside, and saw something odd. I got a pick and picked out a piece of what looked like black carpet. I have to think that someone put it in there, and it was not there from the factory. I put everything back together, and put both clusters in their respective cars. Both work as they should- Hooray!

So someone took apart the cluster to obscure the lit CEL?

Oh, what a wangled web we weave, when first we try to deceive.

This is quite common to the Land Rover Discovery II owners. There is a bogus set of faults that go off for about no reason all the time. Three lights known as the Three Amigos. While it might actually indicate a fault in the ABS or the braking system, it is often just an error caused by dust in the brakes or a slight new sound in the brakes. And it plagues virtually 99.9% of the Disco IIs ever made. A major mistake in design by LR.

So a lot of folks put black tape over the lights before the sell their DII. Wrong but very common.

Welcome to the club.

I too had a Disco with the "three amigos". I got it so cheap ($700), I had to take a chance on it. It had numerous problems, but I was able to fix it up good enough to sell it. It was just stupid things that were fairly easy to fix for me, but the dealer wanted $THOUSANDS. If I didn't buy it, my friend would have let the dealer have it, he just wanted out. I ended up selling it for $3,500. I never want to see another LR again in my life. In fact, I rarely see them on the road anymore. I DO see many in the wrecking yards though, and for good reason. That is where they belong........Rich

Absolutely! I have no idea why, and I suppose I will never know. I have a sneaky feeling the secondary air problem might be the fault of foul play as well. I hope not, but I would not be surprised.

The elegant (mercedes) version of "black tape over the check light"

:D