ammonman

My PSD pump has been kaput since I bought the car. It has been far down on the "to do" list while more pressing needs are addressed. I have always had the "Differential Off" message but no other warnings or issues. With my recent trials with high acceleration knock I borrowed a Bosch "Hammer" to do some troubleshooting. Since I have the Hammer I checked the PSD for any stored faults and it reported the Lateral Acceleration sensor was not giving a plausible reading. After a quick cleaning all was well. The fault cleared and stayed cleared. I even used the Hammer to exercise the Lock Solenoid and found it to be working. Fast forward to last Sunday and when I fired up the car leaving Lowes the dash lights up with "Antiblock Off". Since I still have the loaner Hammer I get home and fire it up. No ABS faults stored, but the PSD reports the Transverse Lock Solenoid has failed. Sure enough, using the Hammer to try and trigger the valve I get no response. I didn't think much about it until today. Since the ABS light comes on immediately when the key is turned and never goes out I discounted the wheel sensors and focused to day on the CEL relay and the two relays on the ABS hydraulic unit. I pulled all three relays for the ABS and bench tested them. All three bench tested fine with +12VDC applied to the coil. I pulled the 12 pin connector off the ABS hydraulic unit and had +12VDC incoming power on pins 6 and 12 which are both direct from the battery. I still can't get the ABS light on the dash to clear. All wheel sensors check good at the wheel barrel plug. I ran out of time to check the sensors at the ABS ECU plug but that is next on my list. Could it be that the Transverse Lock Solenoid failure is causing the ABS ECU to disable the ABS system? I know these two ECUs share inputs and back and forth so that made me wonder. Anyone experience similar failure mode?

The day wasn't a total loss however. I installed a new clamp bracket to keep the air injection down pipe with the bit of busted bracket from banging against the exhaust manifold outlet flange. I also tightened all the exhaust manifold mounting bolts. Some took as much as a 1/4 turn to get tight. Should eliminate some of my cold engine noise.

Just keep swimming... Just keep swimming....


Mike

(Still not ready for a new hobby!)

Arnoud

Hi Mike,

Yes: I have experienced the same ABS warning and experience the similar ABS failure mode some time ago when I took out my faulty PSD-unit (badly seized pump and "fried" pump motor internal coil wiring), while before I had taken out my faulty PSD-unit the ABS was working perfectly. Once I swapped in a fully functional PSD-unit (followed by PSD flushing, as per normal procedure) both the ABS and PSD faults were instantly rectified.
Although I had a large 2.7 ohm resistor bought at the time, I forgot during the swap out to have that temporarily connected to the PSD solenoid connector cabling - so to proof for myself for 100.0% that the the ABS failure mode was purely due to that fact (=PSD-solenoid cable disconnected, leaving an open/infinite resistance type of connection). I still think such to be the case, and will proof that the next time I will service my PSD (not due for a year or so, though...).

ammonman

Thanks Arnoud. I was hopeful that my suspicions were correct. Do you per chance remember the other ratings of the 2.7 ohm resistor?

Mike

Arnoud

Please see hereby further proof why I came to this logical conclusion in the first place (I knew I had these photo's somewhere).

Old PSD-unit removed and measuring solenoid resistance (= fine):

Old PSD-unit removed and measuring pump resistance (short circuit = "fried" coil wiring):


The PSD fuse in the spare wheel well had of course also broken due to this short, so when the old PSD-unit was still in the car the only real connection to the combined ABS+PSD ECU was the solenoid one. Hence by me haven taken the old PSD-unit out, the only thing that changed was the PSD solenoid connection not longer being there. This problem did confuse me at the time for a little while as to why my ABS stopped working and the ABS warning light came on (and yes: I did then immediately checked the drivers rear side ABS sensor and it's wiring, and all was still fine with that of course).

New PDS-unit and measuring solenoid resistance (= fine):

New PSD-unit and measuring pump resistance (=fine):


With regards to your question of other ratings for the 2.7 ohm resistor: if there would be continuous battery voltage on it, then the wattage would have to be ~13V * (~13V/2.7) = 63 watt, which is a huge resistor size wise. However: as I'm rather sure that the ABS+PSD ECU only does a very short pulse kind of sensing as self-test during the starting of the car, I would think that a 5 to 10 watt 2.7 ohm resistor should be more than fine (I did bought a 2.7 ohm 5 watt resistor, and then forgot to test it at the time... ).

ammonman

Thanks for the info Arnoud. This kind of info sharing is what it's all about.

Mike

ammonman

With my "new" used PSD unit installed my ABS fault has cleared as expected. Sure is a strange choice in programming to have a failure in the Transverse Lock Solenoid set an ABS fault instead of PSD fault. I'm sure there is some kind of Teutonic logic behind it but it escapes me.

Mike