SL/R129: No "check engine" light
Thread Starter
Junior Member
Joined: Apr 2015
Posts: 31
Likes: 1
From: so. calif.
1993 mercedes benz SL500
No "check engine" light
I purchased my 1993 Mercedes 500SL April 1 this year. Been in the process of restoring it. I'm second owner, 96K miles but needed lots of work. Took to Smog Man here in So.Cal. and Smog Man said the check engine light doesn't come on when the key is turned on and therefore he wouldn't check it. "Get it fixed and bring it back". I've looked everywhere for an instrument cluster wiring diagram. I need to find out where to start testing the 28 pins on the back side of the cluster. Can anyone please, direct me to a link that has all, or at least the cluster wiring diagram. I checked the bulb and it is good but will not come on. Thanks, James
Member
Joined: Jul 2013
Posts: 126
Likes: 5
From: Saint Augustine, FL
1998 SL500
The connectors on your cluster should look like this:
The Check Engine indicator is not "fed" via either of the round connectors, but rather through the rectangular connector on the left in the above photo--designated as connector 4 by MB. According to the wiring diagrams it is fed by two wires, one red/blue and the other yellow/blue.
The red/blue wire should be at 12V with the ignition on, the yellow/blue wire is a switched ground connection (switched by the OBDI control module N59) and should be at < 1V when the lamp should be on (during the POST and when a malfunction has occurred)...
The Check Engine indicator is not "fed" via either of the round connectors, but rather through the rectangular connector on the left in the above photo--designated as connector 4 by MB. According to the wiring diagrams it is fed by two wires, one red/blue and the other yellow/blue.
The red/blue wire should be at 12V with the ignition on, the yellow/blue wire is a switched ground connection (switched by the OBDI control module N59) and should be at < 1V when the lamp should be on (during the POST and when a malfunction has occurred)...
Thread Starter
Junior Member
Joined: Apr 2015
Posts: 31
Likes: 1
From: so. calif.
1993 mercedes benz SL500
Thank you cliffyk. Great info. However, using my meter, I get nothing and I have the key on. I traced the wires to the fuse box and fuse 1 & 5 were fine. But I still get no reading. I changed to copper fuses to make sure. When I purchased this 500sl I knew there were lots of areas with problems. In fact there was duct tape over the bulb hole and the words check engine was missing. The car is shaping up after working on it for 4 months, part time, and still more to do. But I can't get it smogged here in Calif. unless the check engine lights works properly. Since I've checked those two areas and get no voltage, where do I go from here, where do I check next?? Appreciate any help anyone can feed me. Thanks
Senior Member
Joined: Aug 2006
Posts: 391
Likes: 6
From: So California
2000 SL500
I took my 2000 in for a CA Smog Check and they told me that it would NOT pass Smog due to NO CEL. So the first thing I did was to replace the bulb but that didn't fix it. So I checked the price of an eBay replacement cluster and/or sending it to a Cluster Repair Center. It would have cost me $275.00 w/ S&H either way. So I decided to have my local Indy repair it for $256.50. He ended up soldering the CEL circuit board. VIOLA... the CEL works once again. Since I didn't do the work I can't give you the particulars on how to DIY.
Thread Starter
Junior Member
Joined: Apr 2015
Posts: 31
Likes: 1
From: so. calif.
1993 mercedes benz SL500
check engine fix
Soldered the CEL...That sounds logical. I watched a couple YouTube videos on soldering the circuit board of couple of different things. Be nice if your guy made a video for the DIYer's. I'll figure it out. Thanks for the info
