PeachParts Mercedes-Benz Forum - View Single Post - Retrieving Pre-OBDII Diagnostic Data From ’94 SL500

MB-Dude · #14 10-27-2007, 04:57 PM

First things first… If you own a pre-OBDII Mercedes and have *not* made one of these ‘Home Brew DTC Readers', you are missing one of the best values for your tool box. All the parts are standard at Radio Shack and with an hour of your time, you can build a great little test box. See attached pic. Thanks JimF for basic information and thanks also to Bob Terry for additional info.

Ok, so I made my ‘Home Brew DTC Reader’ and plugged it in. See attached pic. Here are some things I learned the first time I used it:

1. When you plug in the ‘Home Brew DTC Reader’, the LED will be lit until you turn the ignition on. It should then go out immediately with the ignition on.

2. The LED should light and stay on for as long as you hold the button down.

3. If you press the button for less than 3 seconds, the LED will generate a quick, faint flash of light. This indicates you did not hold the button down long enough and no codes have been sent.

Other than that, the operation is exactly as Jim describes on his web page.

So what codes did my ’94 SL500 generate?
Test Pin #19 (Diagnostic Module) – 19 LED blinks
Test Pin #4 (LH-SFI) – 1 LED blink
Test Pin #7 (EA/CC/ISC w/ASR) – 3 blinks, 5 blinks, 14 blinks

The diagnostic code data I have (if I am reading these correctly) indicates (in the order listed above):

A) Injector open or short circuit or emission control system adaptation at limit.

B) Right EA/CC/ISC Actuator (left cylinder bank) (M16/1)

C) Stop Lamp Switch (S9/1)

D) Closed Throttle Position Contact Switch

Now for the fun part… what does it all mean? What I can tell you is what the problem isn’t. I have replaced the main engine wiring harness, gas cap, battery, and did a general tune-up. The car runs great, gets reasonable mileage and passes smog when I 'reset' the CEL. One of the things I have suspected is the wiring that is part of the Main Throttle Actuator. This may help satisfy D and perhaps A.

I’m open to any and all thoughts, feedback and input.

Cheers,
Jeff