Timmer

Hi All –

On a ten mile drive to work this morning after about half an hour (delightful London traffic!) – I had the full monty: Main warning light, PDAS/ABS light plus beeps.

Joy of joys – I can already feel my wallet emptying….

Now, after reading through some of the every valuable posts on here I can give the following detail:

Had a brake flush and fluid change less than 300 miles ago….

Brake pads are less than a year old

Fluid reservoir is full (over the max level) – could this be a problem?

Pumping the brakes with the engine running results in the smaller ( ! ) light coming on for a second or two, and then going out.

Turning the ignition on from cold – can hear the accumulator pump running for about 15secs or so – then it goes off.

Incidentally had a similar problem that was diagnosed as a failed longitudinal accelerometer – which I replaced, seemingly fixing the problem (that was about two months back)

The only other detail that may be relevant is that it has been peeing down with rain for the last two days and I have not had the cover on the car (electrical gremlins??) though nothing appears to be wet…

Sorry to post ANOTHER PDAS light post, but I couldn’t find quite the same situation as mine in any of the other posts in the archive.

Thanks in advance guys,

Tim

(hope to see some of you at Eynsham – hopefully with the 964 )

Edited to Add:

The brake pedal does feel somewhat 'squishy' as well - doesn't bode too well.....

Happy 100 posts

:hehe:

Heirsh

My first thought was ignition leakage, but after thinking baout it perhaps the lights you are seeing are indeed about your 4wd system or related systems. You could look under the hood at night to just check for spark leakage though, wouldnt cost you anything.

garrett376

yeah - this isn't truly the "Christmas Tree" effect - that's when every light is activated for no apparent reason - not just the PDAS/ABS ones...

In your case, the first thing I would look into is removing your spare tire to see if your trunk has flooded and is affecting the grounding points and/or the control unit. You mentioned the car sat out in the rain, so this is the most likely scenario first....

colo964

Try cleaning your ABS sensors. Pull them out and swab off the grindings off the magnets. Or trick your long/lat sensors. I've cracked mine open and "reset" the swinging arm.

Could be the start of a christmas tree. For that do the dark garage test and the AM radio test.

Squishy brake? Try running the booster pump with the pedal at 1/4 then 1/2 then 3/4 then 1/2 etc. Mine was like that after a bleed, then doing the booster cycling I got a burp of something then it was fine.

greenjt

I had the X-mas effect where the lights were random - sometimes only one or two, sometimes a whole bunch and the buzzer. It started only with the lights on and got progressively worse. the problem was either a bad Coil lead or a bad coil. I replaced both coils and leads and haven't had the problem since. Pull the leads off the coils and see how they look.

marcandkimmie

I had a similar problem when I bought my car... except all the lights would come. It had not been driven much by the previous owner. after a couple of months the problem just went away, never to return.

Timmer

thanks for the replys guys -

Have checked out the front compartment and there appears to be no water ingress visible

I have used the car a few times since and every time it is that same -

can hear the pump sounds prior to starting the engine

seems to get to pressure and then stop

once driven for about two or three minutes I get the warning beeps and the PDAS and ABS light come on....

having lookd up this in Adrians book it seems to point to 'static component failure'

In the absence of any test gear - are there any simple ways of finding out what may be at fault? (its a bank holiday here in the UK so all the Garages are closed... )

thanks in advance guys,

TIm

garrett376

Need more info, so test the simple things:
turn on your car and keep it idling - any warnings?
turn the switch on the console to lock both differentials - any warnings?
turn off the switch on the console to release the differentials - any warnings?
with car still sitting still, pump the brake pedal until you hear the pump activate - any warnings?
start driving - if warnings appear, PDAS first, or ABS first, and at what speed?

That kind of info will help figure things out...

Timmer

Hi Garrett - thanks for the suggestions - see answers below

sat in the car idling for three minutes and no warnings at all

no

nope
this is interesting - pumping the break pedal approx five times results in the pump activating - continuing to pump the break results in the PBAS and brake warning light activating temporarily (no alarm)
PDAS & ABS at the same time came on at approx 15MPH both times on the drive that i just went on.

Pumping the brakes vigerously results in the brake warning light coming on but only momentarily (i guess this is normal as the system re-pressurises?)

the brakes seem to be fine but the ABS is obviously not working (tested this with a screeching emergency stop...) -

Is the car relatively safe to drive like this? I guess it is just the ABS and traction control that are not functioning - will this damage any of the mechanicals in the 4wd system?

thanks again folks,

Tim

garrett376

Ok, thanks for the more info. It appers then that your hydraulic system is fine - working exactly how it should. Now we move away from that section of the system.

First off, if the PDAS/ABS warning lights activate, your are correct you will have NO ABS function OR PDAS function. Both systems are disabled at this point. But YES, you can drive the car, you'll just have no ABS or PDAS - it will be like an old 911!

So, if you're moving and the warning lights go off, then you either have an issue with a wheel speed sensor, of which there are four of them, or an accelerometer. If the speed is just 15mph, then it is most likely a wheel speed sensor because the axial accelerometer most often fails at the end of its travel which would be at speed, like 60-80mph. But it could be either problem, or either accelerometer for that matter. Accelerometers can be tested as specified in the Workshop Manual - they receive an input voltage of 5V (pin 3 at sensor; pin 1 is ground), and when sitting level (unaccelerated) they provide 2.7V +/- 0.14 (from pin 2 as sensor; pin 1 is ground) - changing the orientation of the accelerometer will drop the voltage when the car front end is raised.

Hope that helps.

Timmer

Thanks again Garrett -

really confused now, as I took the car to my local shop who have diagnosed the fault as a failed Longitudinal Accellerometer - given that I replaced it a couple of months back (admittably with a used one from ebay) I would think it extremely unlikely for lightening to strike twice.

does this point towards senile dementure of my C4's brain??


(i hope not - coz I've heard that they are really expensive )

Timmer

garrett376

Well, eBay is famous for crappy stuff, so it would not surprise me if that were the case!