On my wife's 91 300TE, the check engine light came on after she turned the engine off. When she started back up it went away. Is this something that needs a dignostic computer to read? How urgent should I try to get someone to diagnose this? Thanks.

I would keep an eye on it. If it comes on again, then go retrieve the trapped code. Occasionally they can inadvertently set a code. If it happens again retrieve the code otherwise, sleep well and just continue to properly maintain the car.

Have a great day,

Thanks Larry, hope it's getting cooler in DFW area. I came from Austin to CT couple of years ago. Don't miss the blistering heat one bit.

That seems a little odd. As I understand it, you are saying that the Check Engine light was on for a period while the ignition was off?

If that's so, that is not normal operation. Normal operation is for the Check Engine light to come on when moving the key to the run position (so you can tell it's not burnt out), then go off after cranking and starting the car. If a fault has been detected and stored, the light will stay on while the car is running.

Do you know how to check the code?

Cheers,
Steve

No, Steve, I don't know how to check the code. That's why I was asking if we need a diagnostic tool for it. I found another thread that indicated I can open up a box and read the number of times LED flashes. Is that what you're talking about? Thanks.

BTW, I didn't see the light. It was relayed to me by my wife over the phone, so I'll see if I can replicate that problem.

I just discovered how to do it myself a few weeks ago when I was having check engine light trouble with my wife's '90 300TE.

Over in front of the battery there is a little black rectangular box attached to the firewall. It has a protective plastic cover you can remove by pulling straight upwards.

Inside you will see a button, an LED, and a bunch of wire connections (pin sockets).

What you do is while the ignition is in the run position, (with the engine running or not), you push the button and hold it for 3 seconds. Then you count the number of times the LED flashes. Sometimes on mine it doesn't seem to work the first time, but the second time it always does.

Flashing once means there is no fault. All the others mean something or other. I've attached a file that gives the mapping of these codes to faults using the LED.

To reset the code you hold down the button for 10 seconds once you've read the flashes.

There are other sets of codes you can access using the other pins in that connector. If you get to it I can tell you how to access them as well.

There's a lot of other good stuff on this in other threads, but I was mystified for a while before I got some basics down.

Good luck*

Steve

Here's the first half of the file (too big to attach all at once)

Attached Thumbnails

 

Here's second half

Attached Thumbnails

 

Wow! Steve, thanks. I'll get to it this weekend when I can spend some time with her car. That chart will help tremendously. Thanks a bunch!

A couple of other things:

The LED only comes on California version cars, I am informed. If you don't have an LED you will have to use the other method which requires a 12 volt test lamp or a volt meter.

This list of faults is only the one for the LED. There are others for the other systems under management, like the engine control system.

Let me know how it goes*

can anyone tell me if these codes apply to 1993 500 sel?

Actually these codes are for earlier models with CIS-e fuel injection. As of model year 1992 all MBs became EFI motronic systems with integrated ignition systems

Yes, the codes above apply to a CA car, not a Federal car. On a Federal car there are only ten different codes and they are read by measuring duty cycle at pin 3 of the round diag. connector.

I have the codes on paper somewhere. I can TRY to find them if you need them for a Federal car.

Have a great day,