| Mercedes OBD1 Fault Codes 1988-1995 |
Got some files you'd like to share with others? I'd gladly put them on this page are credit you. email mercedescodereader@gmail.com Thanks, Rick
| 124 Wire and Plug locations |
Below links courtesy W124performance
| 38 Socket location and details - www.W124performance.com |
| Supplemental OBD1 Code info. for the 119 engine - www.W124performance.com |
| 88-95 w124 w129 Code Reading 38 Socket - Nice article! |
Mercedes Benz C-Class cars Lots of information here
How to Search PDF 2:52
How to clear codes 4:55
How to clear codes 4:55
Peter Davidson in Brandon Florida made a fantastic video on code reading. It's the same procedure for all OBD1 cars with 8,16 or 38 socket cars. Please subscribe to his Youtube channel.
Common Questions and Tips
These 1988-1995 OBD1 Mercedes cars are almost 30 years old so don’t expect code reading to be perfect. Dirt, corrosion, cracked wiring and spider webs all affect the electronics. Especially in the SRS systems.
Why does the LED light immediately turn on when I plug in the yellow?
The LED immediately turning ON or dimly means the system/circuit you're testing has a closed fault due to a stuck relay, solenoid, corrosion on contacts or even spider webs allowing phantom voltage to pass. A typical issue on these older Mercedes.
Finding the faulty part(s) is a process of elimination. The circuit being closed prevents the code reader from receiving pulse voltage from the diagnostic module. I'd start unplugging relays and whatever else you can jiggle around. Then on to swapping / replacing parts.
I always thought Mercedes was stupid designing the OBD1 code system like Christmas tree lights....if one part is fused shut you can't read any codes on that system.
Round socket with 9 holes?
Those cars do not have the OBD1 system. Typically the 9 pin is read with an ohm meter to determine on/off values. I don't have any experience or details on the 9 pin. I do see a video on youtube that may help. https://www.youtube.com/watch?v=5syKYwfEyCo&list=PLg-Bx-y-F2JDJa7AaQWXykPryK8C5yuJS
Want to check if your code reader is functioning properly?
I am not a Mercedes mechanic and know little about fixing Mercedes Cars. I'm an electronics builder / repair guy. My code readers are built here in Kansas by myself. I ship same day so pretty much its 2-3 days anywhere in America. Will my code reader work on your car? Before you purchase Look at the code file and see if the systems you need to diagnose are listed. If your car has an OBD1 connection port buy the one that will plugs into your car.
- One blink or no blink indicates there is no stored code on that system.
- The 8 pin socket does not have a positive post. Use the battery for red.
- 16 socket cars are supposed to have a positive in #16, but not always. You can use your battery positive and negative if you like.
Why does the LED light immediately turn on when I plug in the yellow?
The LED immediately turning ON or dimly means the system/circuit you're testing has a closed fault due to a stuck relay, solenoid, corrosion on contacts or even spider webs allowing phantom voltage to pass. A typical issue on these older Mercedes.
Finding the faulty part(s) is a process of elimination. The circuit being closed prevents the code reader from receiving pulse voltage from the diagnostic module. I'd start unplugging relays and whatever else you can jiggle around. Then on to swapping / replacing parts.
I always thought Mercedes was stupid designing the OBD1 code system like Christmas tree lights....if one part is fused shut you can't read any codes on that system.
Round socket with 9 holes?
Those cars do not have the OBD1 system. Typically the 9 pin is read with an ohm meter to determine on/off values. I don't have any experience or details on the 9 pin. I do see a video on youtube that may help. https://www.youtube.com/watch?v=5syKYwfEyCo&list=PLg-Bx-y-F2JDJa7AaQWXykPryK8C5yuJS
Want to check if your code reader is functioning properly?
- Touch the Red to battery positive and the Yellow to battery negative and the LED should turn on.
- Touch the Red to battery positive and Black to battery negative and PUSH the button and the LED should turn on.
I am not a Mercedes mechanic and know little about fixing Mercedes Cars. I'm an electronics builder / repair guy. My code readers are built here in Kansas by myself. I ship same day so pretty much its 2-3 days anywhere in America. Will my code reader work on your car? Before you purchase Look at the code file and see if the systems you need to diagnose are listed. If your car has an OBD1 connection port buy the one that will plugs into your car.
Got a car with the Push button and LED on the diagnostic socket?
Kent at Mercedes Source is super sharp with Mercedes. See his video above and check out his website. https://mercedessource.com/
If your car has a button and LED test port you can read and clear your codes without an external code reader. If not, you need to buy my code reader which does the exact same thing as the little button does. Except my code reader plugs into each individual socket and gives you flash codes for all your systems.
If your car has a button and LED test port you can read and clear your codes without an external code reader. If not, you need to buy my code reader which does the exact same thing as the little button does. Except my code reader plugs into each individual socket and gives you flash codes for all your systems.
DIY
Build your own OBD1 Code Reader for less than $5. Diagram shows an LED but you can use any 12 volt bulb. The LED makes it easier to count the number of light flashes being quick on and off. Only difference in code readers is the size of the wire ends. Its banana plug for the 8 and 16 socket cars. For cars with the round 38 socket the ends are 1mm or 18 gauge. Also download my OBD1 Code Listing PDF on this site.
