94 sl500 codes and the dreaded harness rot

[edsl94]

hi fellow sl owners. i have a 94 sl w/56k on the odometer, and a 119.972 motor. upon a recent restart the car ran very poorly. got it home, read some threads, made the blink reader( it works perfectly) and pulled some codes from the 38 pin connector. they are as follows:
p4=0
p6=0
p7=6
p8=0
p13=constant l.e.d.
p14=constant l.e.d.
p17=12
p19=6
p21=17
p22=constant l.e.d.
p23=15
p31=0
pins 11,30 issued no response
upon a clearing attempt p6 cleared, p17 cleared to a constant l.e.d.,
p19changed to 7, p21 changes to a 7. also the cel cleared on the dash.

as long as i had the engine exposed i did a closer inspection of the wiring harnes and anyhting not "on" the engine looked fine. but there on top of every injector, the dreaded harness rot. exposed wires just aching to short. do i blow it up now or is there hope?

[fcicco]

I had the same problem with my 95' Sl500 w/119.972 engine. Many trouble codes - they would come and go - cel. A new wiring harness did the trick. Very simple job - about one hour. I got the harness for $550 complete. Car runs strong with no problems 140K+. Many posts on this subject. Good Luck!

[edsl94]

thanks for the reply, i know i'm not the only one with this problem.was the harness a dealer item or did you go through phil? i am going to email him and see what he can do. also, are the harnesses the same as the bad ones just new, or are they better than the original. did you disconnect the battery? i'm also thinking of reringing the injectors while i'm in there. couldn't hurt.

[fcicco]

The harness is a dealer item that does not suffer from "heat rot" or so they say. MB claims that there was no problem with the original. Funny, the dealer I used always stocks two harnesses because they fail early - fail often.
Always try Phil first - probably can get it for you. Email me for pics and more info.

[Terry McNeilly]

Yep, check with Phil . It’s not difficult at all to do the swap. Just lay the new on top of the existing and work carefully. By the way, I replaced the Electronic Throttle harness as well due to its insulation looking just as bad as the engine harness. It was more difficult to install than the engine harness because you have to remove the throttle body. Be very careful of the hot wire sensor element in the throttle body if you do that one also. It's an expensive mistake if you somehow manage to damage it.......like I did.

[edsl94]

on mine, it looks like the wiring going to the throttle body is in the same harness as the injectors and the sensors on the front of the motor. i read on one of these threads where you have to "hand wire" into something on the throttle or linkage, but i don't see anything else in that area that has a wire going to it. how about the battery? does that have to be disconnected when doing the swap? can you change the harness while the car is still "hot"? i'm in no rush to do it, i have other priorities at this time. just building up my knowledge base before i do it. thanks for the replies.

[tecqboy]

Disconnect the battery negative cable whenever working on this vehicles electrical system. All the memory "stuff" is in non-volitile RAM, so nothing will be lost. Some of the electronics is very sensitive, so don't risk damage.

[edsl94]

my concern with disconnecting the battery is losing the radio. as i bought the car used, i have no idea what the code is for the radio. no code card in the owner docs.

[tecqboy]

If it's a Becker, you can get the code from www.beckerautosound.com , but they charge for the service. You need the serial number of the radio. I think any MB dealer can get the code also from the VIN and some MB independent shops too. They simply want proof of ownership. Sooner or later, you'll either need that code or replace the radio with a modern after market radio.

[fcicco]

I did mine without disonnecting the battery. Open your hood and place it in the straight up position. (open normally then press the hinge button on the driver's side then do the same on the passenger side). Remove the plastic panel over the computer modules. The harness is connected with a large plug. Carefully disconnect this plug making sure to slide the plug retainer. This removes power to the harness. DO THIS FIRST! The new harness comes complete with all connectors - no soldering required. When your done carefully reconnect the new plug and slide the retainer closed.

[edsl94]

thanks for the reply! i know just the plug you're talking about as i've already unplugged and replugged just to check the connections. i spent 20 years in the electronics industry. did everything from assembly to process engineering, so i know connections can get crusty. i didn't know about the straight up hood thing though. that will make installing a new hood pad much easier. thanks again!