96 840 both ASC and ABS lights in, help with codes pulled

[vtrek]

Hello all,

I have not driven my 840 much in the past year, and when I got it out the other week both the ASC and ABS lights were illuminated. They never go off now. I've searched the forums and can't find an answer to my specific issue. But I have used all the knowledge I've gained from here to rule things out and test the system.
I hooked my car up to INPA and there are 2 codes:
55 ASC cut-off valve (error frequency 255)
34 ASC change over valve (error frequency 255)

I clear the codes but the lights never go off and the codes are back the next cycle.

I have scoured the forums and the net and cannot get a firm answer on what these valves are, what they do, and where they are in they system and how they malfunction.

I have had the batteries stressed tested and they both passed. The car is always on a trickle charger when parked. The voltage at the terminal under the hood is 12.4v and 14v when the car is running. I know how sensitive this car is to voltage. Years ago my batteries were failing and it tripped the above 2 lights until I replaced the batteries (did not pull codes then). But this time by batteries appear fine. These batteries are about 3 years old.

I also removed the ABS pump relay and jumped the connectors. The pump runs fine. *But the car does not do the self asc throttle test anymore when the key is turned on (the burr burrr noise). This stopped when the lights appeared. I assume this is related to one of the valves above? Here is where it gets a little strange. When I turn the key on, the asc throttle actuator does not cycle, BUT when I attached the car to INPA and enter the ASC menu, the actuator cycles. I do not prompt it, I just enter the main menu. At least that shows me the actuator works. The cable appears taut and is routed the correct way. I can see the throttle cycling.

If I do try to activate any valves or actuators via INPA, nothing happens. I activate the ABS pump, INPA says "running", but nothing. There is a command to active the ASC cut off valve (whatever that is) but I hear nor see anything. Could that point to an issue with the ASC/ABS module? That was my next step. I accessed the module by the driver's seat and disconnected it. There is no water, signs of prior water, corrosion or damage. All pins look fine. The lights are still illuminated while the module is unplugged. When I plug it back in and again go to INPA and go to the ASC page the secondary throttle activates and cycles.

I have not inspected the wheel sensors as the codes point me in a different direction, should I? Would that stop the system from even doing the initial self test? Any suggestions are much appreciated. Thanks in advance, John

[Timm]

It is very unusual for the ABS/ASC hydraulic block to fail - and it is certainly strange that TWO valves have failed at the same time. You also say that INPA is not activating the valves, but I cannot say for sure if you actually hear anything anyway! The test for the ACT actuator I use is to run the ASC pump from INPA - when it finishes the test the secondary throttle should do a test - I'll look into the error codes later just to make sure they are correct....

[Timm]

The error codes line up with what I have here - as I said earlier, the hydraulic block rarely goes wrong - here's a cross section of the unit used for DSC but has the same internals as the ASC+T:

Fullscreen capture 14032023 211138.bmp.jpg

...that shows the valves that are referenced in the error codes. My thoughts are to check the hydraulic valve relay (which is next to the pump relay): http://www.meeknet.co.uk/e31/Timms_B...lay_Finder.htm

Swap them over (the pink ones are identical) and see if the error codes change - if that doesn't work then try re-seating and cleaning the connector that connects to the hydraulic block. It is hard to get to from the top (but can be done), but a lot easier through by removing the left-hand wheel liner

[Timm]

[vtrek]

Thank you Timm for all the information! I will first thing try the is to swap the relays. I had previously checked out your e31 bible, that gave me the idea to test the pump. I did swap the relays, but never checked the codes afterwards, just saw no change in the ACT self test of the lights (now I see my error in hindsight) and switched them back.

Next I'll dig into the the connector of the hydraulic block. As you state, it would be odd for 2 valves to fail at once, let alone 1.

*If the module detects what it sees as a fault in the 2 valves (whether they have failed or the connection is bad) would it abort the rest of the ASC set test when the key is turned on (and that is why I no longer hear the ACT cycle)?

Again, super appreciate your help, I see the system a little more clearer now.
John

[Timm]

I'm not sure - I only have experience of the pump failing and what INPA can do to diagnose the problem. But, I would have thought that if there is a problem with the hydraulic block then the ABS and ASC+T would both be disabled

[vtrek]

UPDATE

Not a great one. I had the car out over night, and it rained here in SoCal, a lot. Once it stopped I started back in. I reversed the relays and as soon as I turned the key on I heard the relays clicking, and the ABS pump going on and off frantically. I turned the key off and INPA could not access the ASC module. I went back and looked back at the module I saw that there was standing water under it. I pulled up some of the carpet and its really wet under there. GREAT

I pulled the module out and the bottom of it was touching the water that had pooled under it. I opened the module, and yep, the bottom 1/8 of an inch of the circuit board has a water stain and is slightly corroded. It was wet, so I assume it was causing all the relay commotion while it shorted out. So I will source a new module.

I pulled the carpet further back, and I think I can trace the water to behind the accelerator petal, all the way up behind the floor vent under the dash above the accelerator. Is water getting in from the fresh air intake under the windshield wipers? Is there drainage holes that may be clogged somewhere? Before I start tearing things apart, thought I would check if this is a know issue with the E31's. It's really wet under the carpet, which is concerning. But the car is hardly ever in rain (its been in SoCal its whole life, so from what I can see it never reached much of the wiring area the firewall, and there is no corrosion on the body ground next to the ASC module. So good sign this is a new-ish water leak ( I'll take any silver lining I can).

Thanks again
John

[vtrek]

Just to wrap up this thread, thanks to everyone who helped out. It turned out that I did have fresh water intrusion that touched the ASC module. Thanks Timm for helping me understand the codes and seeing it was most likely a wiring issue and not a abs valve issue. That lead me back to the module and pull the carpet back more. Thanks to Cartoonz I got a replacement module that as soon as I plugged in the dreaded lights went out. Drove a 100 miles and she is all good.

Feels good to drive the car with no dash lights on! Again, thanks everyone.

[Timm]

Great stuff, well done!