How to remove ABS controller connector

TorqueHead · TorqueHead's Garage

I am trying to remove the multi-pin connector that goes to the ABS controller in the frunk (passenger side) without much luck. 1992 964 C4.

I removed the phillips head screw at the back end of the connector, and operated the lever which raised the front part of the connector but I cannot free up the back side of the connector. I don't want to pull too hard for fear of breaking something.

There is a plastic clip at the back that looks like it will release the connector if you angle the connector up, but I get too much resistance when I try to angle it up. I have studied the clip to see if you need to press something to release it and have poked at it gently but again I am afraid of breaking old plastic.

I have searched for the solution but cannot find a thing. What am I missing?

What's the secret?

TorqueHead · TorqueHead's Garage

Update:
Connector successfully removed.

After exerting as much force as I dared to (without success) I decided to tackle the problem in a different way. I unbolted the controller. It is held on by two nuts, one of which had easy access, the other one was a pain but with a pair of long nose pliers I was able to undo it.

Once I had the controller unbolted and moved it away from its location, the connector practically fell off. I still don't know exactly why this method worked. My current theory is that the wiring harness which is heavy, bulky and stiff is what was the cause of the resistance. I guess I should have removed more of the cable clips. I removed two of the clips but perhaps removing the third clip would have done the trick.

Anyway I thought I would post my info in case anyone else has a similar problem. The cable clips can be pried off and can probably be reused but new ones are available for $1 each. Part number is 999 513 049 40.

The good news is that the connector and pins all look good. No corrosion and the innards of the controller look clean and dry. Now I need to figure out why it keeps blowing fuses.

OSC911 · 03-10-2021, 11:34 AM

Great info - thanks for the update

LM964 · 03-11-2021, 01:36 AM

Yes, that is a very bulky cable and connector. Moving it into a shape or position to make movement easy, isn't easy!

TorqueHead · TorqueHead's Garage

Quote:

Originally Posted by OSC911

Great info - thanks for the update

No problem. I am happy to contribute to the wealth of knowledge on this site.

TorqueHead · TorqueHead's Garage

Quote:

Originally Posted by LM964

Yes, that is a very bulky cable and connector. Moving it into a shape or position to make movement easy, isn't easy!

Exactly, but until I unbolted the controller, I had no idea just how rigid the cable was.

On another note, does anyone know if it is ok to start the engine with the ABS controller disconnected? I realize this means no ABS and no PDAS but I don't plan to drive it, I just need to run the engine for a bit.

LM964 · 03-12-2021, 12:23 AM

Quote:

Originally Posted by TorqueHead

On another note, does anyone know if it is ok to start the engine with the ABS controller disconnected? I realize this means no ABS and no PDAS but I don't plan to drive it, I just need to run the engine for a bit.

Should be ok I would have thought. Just the dash lights will be telling you otherwise. Why do you need to fire up the engine w/o the control unit connected?

LM964 · 03-12-2021, 12:28 AM

Quote:

Originally Posted by TorqueHead

Exactly, but until I unbolted the controller, I had no idea just how rigid the cable was.

The control unit connector recess is a water trap (rain, car washing etc). Not unusual after a couple of decades to see some corrosion on the pins (both male and female). Pins are fragile but I did have one or two looking not so good. Very gentle cleaning fixed this in my case. One idea is to press into the connector recess gap a short length of rubber window seal or similar.

TorqueHead · TorqueHead's Garage

Quote:

Originally Posted by LM964

The control unit connector recess is a water trap (rain, car washing etc)... One idea is to press into the connector recess gap a short length of rubber window seal or similar.

Yes, my research did lead to water ingress as a known problem. I will definitely look into some form of water-proofing or relocate the controller. One owner turned the controller upside down so the recess cannot fill with water.

The reason for wanting to start the engine without the controller is just to run the engine once in a while, while I get the controller fuse blowing problem sorted. It has been almost two months since the last start of the engine, and apparently it is better if they don't sit for extended periods of time. I also may need to start it up for other work that it needs done.

LM964 · 03-13-2021, 02:10 AM

Are you able to borrow and test swap a control unit over with someone else who has a C4? AT least then you can eliminate the control unit as the cause or some other cable/earth/other item. Maybe it's already been mentioned..

TorqueHead · TorqueHead's Garage

Quote:

Originally Posted by LM964

Are you able to borrow and test swap a control unit over with someone else who has a C4? AT least then you can eliminate the control unit as the cause or some other cable/earth/other item. Maybe it's already been mentioned..

It's a great idea but sadly I do not know of anyone else with a C4 in my area. I am currently searching for a wiring diagram just for the ABS/PDAS. The electrical diagrams for the entire car are so complex I find them hard to follow.

bazar01 · bazar01's Garage

Quote:

Originally Posted by TorqueHead

The reason for wanting to start the engine without the controller is just to run the engine once in a while, while I get the controller fuse blowing problem sorted. It has been almost two months since the last start of the engine, and apparently it is better if they don't sit for extended periods of time. I also may need to start it up for other work that it needs done.

The biggest load that could blow the fuse is the pump motor. The rest are just relay solenoids on the pump which could fail shorted. Open coil will not blow a fuse.

Which fuse is blowing? 40A or the 5A?
40A supplies the booster pump
15A supplies the ABS computer.

I have a wiring diagram for 1992 Porsche C4 ABS (Dynamic AWD Control)

TorqueHead · TorqueHead's Garage

Quote:

Originally Posted by bazar01

The biggest load that could blow the fuse is the pump motor. The rest are just relay solenoids on the pump which could fail shorted. Open coil will not blow a fuse.

Which fuse is blowing? 40A or the 5A?
40A supplies the booster pump
5A supplies the ABS computer.

Thanks Bazar01. It is fuse #16 (15 amps) noted as being for ABS.

bazar01 · bazar01's Garage

Fuse #16, 15A goes to:

- ABS computer to pin 28
- ABS relay R34 pin 30. then to pin 87
- R34 pin 87, to Rotary switch for lock control pin 3 to pin 1 to ABS computer pin 28
- ABS relay R34 pin 87 to ABS computer pin 1.

Put a DC clamp meter on the wire for each pin one at a time and see how much current it draws and hope to find out which one is blowing the fuse.

Use a test light with clamp connected to B+ and start checking ground connections.

Also test the solenoid valve outputs for the rear, FR, FL at the ABS computer for resistance to check for short.
Rear at pin 2, FR at pin 22, FL at pin 19

TorqueHead · TorqueHead's Garage

Thank you so much Bazar01,

You just saved me a ton of research time.
I had a quick chance to look at the car this afternoon (before I saw your post). I pulled the relay R34 and shook it. Is it supposed to rattle?

Anyway I will bench test the relay and then continue with your instructions.

bazar01 · bazar01's Garage

Yes R34 rattles. I just pulled it and shook it a little.

TorqueHead · TorqueHead's Garage

Good to know. So it looks like pin15 is positive and pin 31 is negative for 12 vdc power supply for relay testing. The coil measured 94.5 ohms.

bazar01 · bazar01's Garage

Don't think the relay can blow the fuse.
You need to check the loads on that circuit.

TorqueHead · TorqueHead's Garage

Ok, I have my work cut out for me then. Thanks again Bazar01.

TorqueHead · TorqueHead's Garage

Before moving on, I noticed that the R34 ABS relay contains a zener diode and a resistor, so it is not just a simple relay. I tested the diode and it is shot so I opened up the relay.

The "rattle" was a thin piece of what looks like a phenolic insulating board that was loosely fitted but still able to cover the PCB. So, there is one mystery solved.

The relay OEM was VDO Beck-Arnley. I am trying to source a new diode but it does not look promising so I may have to shell out the $100 for a new one, but if something else caused this one to fail and if I don't fix it, the new relay will also fail. So the hunt for the root cause continues.