apw964

All,

I need your help please - I'm having problems with the PDAS and ABS lights showing. I've read through the archieves and couldn't find anything to help fix my particular problem

Details of Car;

1990 C4 (Registered Nov 89)
Design 90 wheels replaced with after market 17 ' Cup I wheels
Tires Front 205 x 50 x 17 (Bridgestone s03)
Tires Rear 255 x 40 x 17 (Bridgestone s03)

Previous Issue Fixed;

I was having the same problem a lot of the folks have described where the ABS seemed to initiate too soon and then pulse making the braking seem inaffective. To resolve this problem I followed the advice and cleaned out the Longditudinal and Lateral Sensors - Problem Solved !

Current Problem;

When starting the car the the PDAS and ABS lights show (as they should) after 30 seconds or so they switch off (again as they should). After approximately 15 mins of driving the PDAS and ABS light comes on. If I shut the car off and start it again the lights go out after 30 seconds or so again, but come back on again after 2-3 mins. If I leave the car for a longer period of time the lights take 15 mins to come on after the initial start up sequence. (The buzzer also sounds when the lights come on)

Things that I've checked;

1. I've pulled all of the wheel sensors and cleaned the contacts and some light metal filing accumulation from the tips of the sensors

2. Re-checked the Lateral and Longditudinal Sensors - all seems ok

3. Checked all Grounnds / Earths - all seems ok

4. Checked that the Diff locks engage using the switch in the centre console

5. Checked the relay - seems to get very hot !!!!!!

So - any idea's folks ? My guess is that the relay getting hot is something to do with it, is it a case of simply a duff relay, or is that just a result of a bigger \ different problem ?

Thanks

Andy

J Henry

Yes, Having the same problems & tried all those fixes. Think it may be electrical interference & will fit a new set of spark plug leads. Have already changed the 2 dist. caps, rotors & coil leads.

apw964

J Henry,

Let me know how you get on. Also - is your relay getting hot ?

Thanks,

Andy

Adrian

Dear Andy,
The first thing that comes to mind is that you may have damaged one or both of the accelerometers.
For the PDAS and ABS lights to come on whilst driving after a period of time tends to suggest it will be a dynamic component. This is a component which requires movement of the 964 before a failure can be detected.
These include;
Dual solenoid valve not opening correctly
One of the differential locks not functioning correctly most likely the centre diff lock based on your symptoms.
Control unit internal failure.
The relay should get hot by the way. It provides power to the whole system.
I would also advise that you check for water in the connector of the PDAS/ABS control unit.
Ciao,
Adrian
911C4

PS: If the tech pages are up please read the article I wrote. It might help.

apw964

Adrian,

Can you recommend a way that I can check / test these components at home without the use of a hammer;


1. Longditudinal and Lateral Sensors
2. Dual solenoid valve
3. differential locks
4. Control unit internal failure.

I assume that with #4 the only real approach is to find someone willing to loan me their control unit, but for 1 - 3 is there anything I can do at home ?

Thanks

Andy

apw964

Folks,

I am still having my abs / pdas warning light issue - see above. I recently tried a borrowed relay but the problem did not stop. I would like to tackle the problem from a cost perspective, so I would like to determine next if the speed sensors are functioning correctly. I have removed all of them and cleaned the sensor connections and heads. Insidently the heads of the sensors had a very light coating of iron filings. Couple of questions;

1. Does anyone know if there is a way to test their condition without the hammer ?

2. Assuming that they are bad, any idea how much they cost ?

BTW - the reason I have a hunch about the sensors being the issue is that the problem occurs after approx 15 mins driving, and then when you restart the car immediately the lights come on within 30 seconds. If you let the car cool however the lights will take 15 mins to trigger. I believe then that it is a heat related issue, and now that I've tested the relay, this seems to be the next logical place, with heat build up coming from the brake rotors ? Also as I recall the first time the lights triggered I was travelling over bumpy ground !

Thanks

Andy

Adrian

Dear Andy,
You can resistance check your sensors. However from your symptoms I do not believe your problem is the sensors. This sounds like brake fluid related which takes me to the diff locks. I would suspect the centre or longitudinal diff lock based on previous experience. Heat from the brakes is minimal and these are inductive pick ups and not affected by heat unless they are totally failed. They are designed for this environment.
I really feel you need a hammer hooked up otherwise you are going to be going around in circles and also run the possibility of creating additional problems. I know I did it and when I found what I had inadvertantly messed up (wheel sensor connector) I thought I had the problem solved. Wrong, it finally took a hammer to help me out.
Ciao,
Adrian
964C4

Carl Muckenhirn

Andy's problem sounds exactly like the problem I had which was fixed with a new set of plugs. My wrench changed the plugs for me to fix a rough idle (which didn't fully fix it). At the same time he was fitting a new set of rotors, and also a pair of new calipers in the back. Immediately the PDAS/ABS problem cropped up. WOuld go from tirggering every 5 minutes, to not at all for a long (300 mi) ride.

He check the accelerometers, swapped them all out. Checked all the wheel sensors, grounds at the sensors, ... To no avail.

The plug swap though induced an audible arc in the engine compartment (between 2 and 3, could see it in a dark garage).

After replacing that bank all was well (changed the other bank the next weekend, what a pain!).

I'd suggest trying new plug wires (or atleast check the resistance of all of them, though that won't show an arc caused by breakdown of the insulation.

carl.

apw964

Guys,

I swung by my mechanics place yesterdy, and lucky for me he's just bought himself a sytstem II tester - a very fancy piece of kit, about the same size as a laptop which has the same functionality as the hammer.

The diagnostic indicated that my longditudinal sensor is duff. As these things are so expensive to replace I took it upon myself to remove sensors again and give them one final clean. I thought I had cracked it as the problem took longer to occur, but unfortunately the problem did strike again.

Any one happen on the off chance to have a spare longditudinal sensor I could buy ? I believe from looking at the part numbers that the longditudinal and lateral sensors are actually the same part ???

Thanks

Andy