De-pinning Motronic 1. 3 DME 55-pin connector

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x_atlas0

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Hey, everyone, I'm a bit stuck and figured I'd ask the community.

I recently discovered my coupe thinks the non-existent AC compressor is active, throwing off my idle and general behavior. I can't find the source of the signal in the engine bay, so I wanted to try and pull the pin from the connector to shut it down. I found this post that had some details, including describing the lock bar in the connector itself: https://rennlist.com/forums/924-931...ning-the-bosch-55-pin-dme-connector-plug.html

I managed to get everything opened up, disengaged the lock bar, but I still can't get any pins out of the connector. I can't push or pull the pin I want out, and there doesn't seem to be any sort of locking tab hole I can insert any tool into to disengage the lock. I'd like to hear some tips, tricks, or pictures showing what I have to do to get the dang pin out. I also tried this on 2 other harnesses I have around, and I can't get the pins out of any of them.

Thanks for any help.
 
sfdon said:
Just snip the black/gray wire to pin 40
no need take the pin out
Click to expand...
I was thinking that as a last resort, as I want to be able to add AC back later. If I cut it now, then I'd have to remember cutting it and re-do the splice under the connector trunk when I add AC, if I'm going to use the Motronic ECU. I've been using this pinout as a guide:
1735936686093.png

1735936715133.png



Unfortunately, I can't seem to trace the source of the signal, as under the engine bay, there's nothing over by where the compressor goes as even a start.

I was hoping it had the small white 4 pin connector that is the normal source for this close to the DME, but no luck.
 
Last edited:
The signal comes through the dash, not from in the engine.
 

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I am confused, if you have an ON/OFF switch for the AC this signal would not affect idle when it is OFF.
Perhaps put the switch and circuitry even without the compressor?
 
Last edited:
Arde said:
I am confused, if you have and ON/OFF switch for the AC this signal would not affect idle when it is OFF.
Perhaps put the switch and circuitry even without the compressor?
Click to expand...

Right now, I think it's getting battery voltage, so the ECU thinks the compressor is on, which seems to be raising my idle when closed-loop is on. I can't check it without backprobing it while the car is running, which is challenging because the connector is in the glovebox.

sfdon said:
The signal comes through the dash, not from in the engine.
Click to expand...

Which Bentley manual is that from? I don't see that drawing number in my E34 copy.

I thought it came off the multi-pressure switch based on this:
1735972678957.png
 
x_atlas0 said:
Right now, I think it's getting battery voltage, so the ECU thinks the compressor is on, which seems to be raising my idle when closed-loop is on. I can't check it without backprobing it while the car is running, which is challenging because the connector is in the glovebox.
Click to expand...
I am guessing here, but if the ECU uses this input as a digital input, then an open circuit is not a good plan. The voltage would be floating and may interpreted as on or off depending on many things. Battery voltage would mean it is more an analog conditioned input and may have pull down resistors so open is fine.
 
To answer the original question, the pins have very small tabs that splay out when inserted into the connector. These hold fairly well, even when the connector is loosened up. You can usually set the connector against something solid and knock the pin out with a very small pin punch or a pick. This will probably destroy the tabs on the pin, so that you need to replace the pin if you want to use it in the future.

I don't know whether this is the right solution in your situation, but it you want to get the pin out this should do the trick.
 
If you are using a 179 Motronic ecu in your coupe - there is no connection to pin 40 black/gray wire in the engine harness from the chassis harness. There is no reason for that wire to be hot. If you add AC you can connect AC 12v+ to pin 40.
 
control relay to high and low pressure switches to DME.

you don’t need to check voltage because you have none of those and therefore no voltage at pin 40

you absolutely can check voltage at DME connector - remove 3 screws, rubber seal, pull connector out of cover and push connector back onto DME .
You pin the backside out.

you have my phone number?
 
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