ABS PSD Warnings after bump on '90 GT

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22 Nov 2011 19:55 #7083 by srshaw3
Since getting my '90 GT back from service, the ABS & PSD warnings are displayed apparently after the first significant bump. Often they display at the same time, but sometimes the PSD followed by the ABS.

I am presuming it is a loose connection, and more likely rear of the car related since I don't think the PSD would care what happens at a front wheel. Any thoughts on what connections and where to check? Perhaps removing the two grounds at each rear wheel to start? They seem solidly connected when tugged at a bit.

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22 Nov 2011 20:35 #7085 by the flying scotsman
The ABS and PSD circuits are linked through the fuse/ relay panel.....I'd check the relay (XV) to start.

Has the PSD system been serviced (fluid flush)?

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22 Nov 2011 20:43 #7086 by srshaw3

The ABS and PSD circuits are linked through the fuse/ relay panel.....I'd check the relay (XV) to start.

Has the PSD system been serviced (fluid flush)?


I will re-seat the relay, inspect the pins, etc.

Yes, the PSD was flushed a year ago and operated fine after that. I suspect this issue has arisen due to the quite a bit of electrical diagnosis type work that was performed.

Thanks Malcolm.

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22 Nov 2011 20:47 #7087 by the flying scotsman
no worries Stan.......beyond the relay Id look at the controller and the ABS sensors.

We are a captured audience for ~4 mths......damn winter:eek:

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23 Nov 2011 05:48 #7092 by srshaw3
The rear abs sensors were my first thought.
I anticipate I am looking for a component in common between the ABS and PSD.
Do you know if they are used by the PSD?
Do you think I should remove clean and reinstall? Just looking at them I don't see an issue.

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23 Nov 2011 21:45 #7098 by the flying scotsman
Yes, the ABS sensors are part of the shared PSD circuitry.

Yes, they can be cleaned, I use use brake cleaner and a small brush (toothbrush).

There are resistance spec for the ABS sensors.....let me find them

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27 Nov 2011 12:14 #7152 by srshaw3

no worries Stan.......beyond the relay Id look at the controller and the ABS sensors.

We are a captured audience for ~4 mths......damn winter:eek:


I swapped the relay with a spare I had, no change.
I guess I will review the sensors more thoroughly now.

I also found my special positive battery cable bolt (that has a fixture for 3 wires to attach) is a bit stripped). I wonder if it could be causing an issue. I will replace it as well, but the car starts fine and I would suspect other electrical issues is this was causing the problem.

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27 Nov 2011 12:58 #7154 by xstepson
Stan,
I am awaiting your further diagnosis on this issue. My '94 does the exact same thing. I also have been wondering what the two systems have in common that would be causing this.

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27 Nov 2011 13:10 #7155 by 928mac

Since getting my '90 GT back from service, the ABS & PSD warnings are displayed apparently after the first significant bump. Often they display at the same time, but sometimes the PSD followed by the ABS.

I am presuming it is a loose connection, and more likely rear of the car related since I don't think the PSD would care what happens at a front wheel. Any thoughts on what connections and where to check? Perhaps removing the two grounds at each rear wheel to start? They seem solidly connected when tugged at a bit.


Stan you say when you got it back from the service this started. Was the light on before? If not, is it possible the bat went dead in the shop on them, or that they boosted the bat.

but

Lets think now, if they had it on a lift to change oil, what could have changed?

If the wheels and suspension hung down? what could have been pulled loose?
What kind of connections are around the diff for the PSD.

Look closely at the ABS cables/sensors following along every mm for a tell tail sign where it may have snagged when the car was lifted. I would not rule out the fronts, look close with a light.

I dont know our ABS system but they are all similar. The ABS and PSD would have to work together as well as the ABS work separate.
What worries me is if they somehow fried the module by boosting the Bat.

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27 Nov 2011 18:26 #7157 by srshaw3
Unbolted and clean both rear speed sensors, and also unbolted and cleaned both ground connections. result: no change in symptom.

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27 Nov 2011 19:49 #7158 by the flying scotsman
with a good dvm check resistance between sensor termails then each terminal to ground.

dont have specifics in front of me but readings should be ~20k ohms (infinite) to ground

found it:

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28 Nov 2011 23:07 #7174 by SeanR
Acceleration sensor under you seat is gummed up. Do not replace it, do not screw it up when you take it apart. It's a $1500.00 item they developed for the 959 and it made it's way to the C4 and our cars. :D

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29 Nov 2011 08:31 #7175 by srshaw3

Acceleration sensor under you seat is gummed up. Do not replace it, do not screw it up when you take it apart. It's a $1500.00 item they developed for the 959 and it made it's way to the C4 and our cars. :D


Really?
I have a rattle somewhere near the passenger seat, is it there?
Thank you!

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29 Nov 2011 11:13 #7183 by 928mac
Is Sean joking, I thought he was till I saw the price quote. :eek:

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29 Nov 2011 21:51 #7201 by srshaw3

Is Sean joking, I thought he was till I saw the price quote. :eek:


Not joking apparently:
forums.rennlist.com/rennforums/928-forum...leration-sensor.html

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30 Nov 2011 11:04 #7210 by 928mac
Hay Stan, that is a good thread.
I didn't know there was such a thing in our car.
Hmmm this reminds me that while on vacation, I pulled up to a stop sign on a very steep incline.
When I lifted my foot from the gas to move it to the brake, the brakes applied (the car stopped rolling back).
I found this weird and touched the gas to bump the car forward and it would not roll back as if I had stepped on the brake.
I wonder if this is due to this little device.

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