C4 PDAS & ABS Warning Lights?

mcgc0 · Dec 9, 2012

Bit of a funny one this one...

From cold, ignition on and can hear the boost pump etc doing it's noise stuff until up to pressure. Start engine and after a few seconds all warning lights go out (ignoring parking brake) - all except the 4-wheel drive PDAS and the ABS lights. Still stationary. Wait a further 1+ minute and both lights still remain on. No warning buzzer (as I haven't started moving off yet). Fluid reservoir at max btw.

Start moving off and continue to drive thinking maybe wheel speed sensor or diff locks related, both lights remain on with no warning buzzer - hmm... However, start to get up to speed (50+mph) and they go off. Ah, must be speed related me thinks. But, when stationary at lights they still stay off and the problem doesn't reoccur for the rest of the journey. Confused me for a while during the course of a few short test trips - each producing the exact same results.

Ah ha, today and getting closer to the issue (I hope); discovered now that it isn't wheel speed related - it's engine revs!?! Stopped off after a short run where the lights had eventually gone out as before. Restarted engine and both lights back on again - damn! However, blipped the throttle while stationary to 3k+ rpm and both went out [&:]. Able to faithfully reproduce the same result each and every time. Happier now that the problem is consistent under the same test condition but of course non the wiser as to root cause - Instrument gauge? Relays R34 (ABS) or R51 (Brake Boost Pump)? Fuses?

chrism964 · Dec 9, 2012

Faulty clock?

Could be a faulty battery - if Voltage less than 9.9v then, according to Adrian Streather's book, you get the symptoms you describe. Might explain why revving helps because then your alternator will be providing more juice.

HTH

Chris

ras62 · Dec 9, 2012

Possibly voltage related? If the voltage has dropped below 12.6v for some reason the system can throw up faults, as the revs build it could be high enough to reset the alarms. Worth a check with a multimeter.

bernard tester · Dec 9, 2012

Hi Marcus try cleaning up the battery connections, clean up the leads and small wire abs pump to earth. and as has been said check battery voltage and charge rate. Regards Berny.

PaulR964 · Dec 9, 2012

I agree with ChrisM964 who thinks it might be the clock. I had exactly the same problem years ago and eventually replaced the clock. Subsequently I have read that there's a possibility of a dry joint within the clock that can be resoldered to solve such a problem. I have seen a description written up but can't recall whether it was on one of these forums, or in the 911 and Porsche World magazine. As I recall, putting a voltmeter on the battery showed that the point when the lights go off coincided with the alternator starting charging, after which it carried on charging when the revs were allowed to drop back to normal idle. Hope this helps, ... Paul.

mcgc0 · Dec 9, 2012

Good points. I have a spare brand new battery (from the prev 964) - although uncharged for the last 5 months (presuming a full charge will bring back it to normal use). Will swap this over and check wiring points to ABS pump and nearby earth points.

Read Streather's fault diagnosis earlier re 9.9v but slightly confused with the problem and diagnosis text - no traction control LED ever on (mind you can't get it to go on with the manual switch so the LED may be faulty), and also suggests lights go out when moving forwards, which I don't need to be (just the throttle blip). Maybe just the revs increase rewrite this a bit.

mcgc0 · Dec 9, 2012

I agree with ChrisM964 who thinks it might be the clock. I had exactly the same problem years ago and eventually replaced the clock. Subsequently I have read that there's a possibility of a dry joint within the clock that can be resoldered to solve such a problem. I have seen a description written up but can't recall whether it was on one of these forums, or in the 911 and Porsche World magazine.

Cheers Paul, I'll look at the clock too. I also have a spare clock which is good.

ras62 · Dec 9, 2012

When swapping the battery I would also change the earth lead to the new type, the old ones can look fine but break down internally. It can cause all manner of gremlins.

Steve Brookes · Dec 9, 2012

I had the same problem. Albeit that I only had the ABS light stay on seeing as mine is a C2. As soon as I blipped it past 3,000 rpm, the light would go out. I checked the charging when starting the car cold and only got 9.8 volts. It zipped up to 13.5 volts as soon as I blipped the revs past 3,000. Basically, the alternator wasn't being kicked in to charging on initial start up. I thought the alternator was on its way out but the problem disappeared when the fan belts were changed at the last service!

mcgc0 · Dec 9, 2012

Interesting Steve. Ollie at RPM gave the engine a 12k service when he had the engine out a short while ago, he mentioned belts were changed then. I'll check with him what belts and look at the current tension.

Actually thinking about it... coincidentally, I have an intermittent belt 'tensioner' light-on from time to time. As I knew the belt is still there(!) and the sensor wheel were it should be, I had thought it may be a dry solder joint with the gauge. Swapped the gauge over but it still occurs from time to time (not every journey though). Right, I'll check the belts first then before moving to the front...

Cheers

mcgc0 · Dec 9, 2012

ORIGINAL: ras62

When swapping the battery I would also change the earth lead to the new type, the old ones can look fine but break down internally. It can cause all manner of gremlins.

What's the "new type"..?

ras62 · Dec 9, 2012

ORIGINAL: mcgc0

ORIGINAL: ras62

When swapping the battery I would also change the earth lead to the new type, the old ones can look fine but break down internally. It can cause all manner of gremlins.

Click to expand...

What's the "new type"..?

Old style is braided, the new ones comes insulated. My old lead looked fine but gave some odd readings depending upon where on the lead the reading was being taken from.

mcgc0 · Dec 9, 2012

Weird... will check (not something you clock normally) and will replace regardless. Good tip - thanks.

Melv · Dec 9, 2012

Batt prob -my Shogun does same

Also worth cleaning up all the earth straps

ras62 · Dec 9, 2012

ORIGINAL: mcgc0

Weird... will check (not something you clock normally) and will replace regardless. Good tip - thanks.

LOL, very true and it surprised me also, but being the anal engineer type I noted the difference. Cant take the credit though as it was my Indy who told me they go bad before showing me.
Incidentally I have just read the CC 911 review, great to see your car came out with high praise amongst some seriously fine cars! A good little article actually and nice to see the 964 getting good press again

Best. Rob

mcgc0 · Dec 10, 2012

ORIGINAL: ras62
Incidentally I have just read the CC 911 review, great to see your car came out with high praise amongst some seriously fine cars! A good little article actually and nice to see the 964 getting good press again Best. Rob

Cheers Rob. I'm seriously beginning to think I should also be looking at grabbing a good looking 964 Turbo too - think they will start to split away from the rest of equal margin before long (ignoring the specials and RS of course).

gregmarshall · Dec 10, 2012

Hey man,

Agree with battery charge being the most likely cause.. have you not got your trickle charger plumbed in? don't forget you get a bit less battery performance when the weather is cold too.

Just about to change my old style earth strap out.. looks a bit manky :

Also if your PDAS light is not coming on and it's an original filament bulb that's blown, they're soldered to a little board... easy mod to LEDs though.

G

mcgc0 · Dec 11, 2012

Cheers Greg. CTEK trickle charger always on, but with the battery that came with the car (not sure of the age/history). Rather then mess around I will swap for the new battery I got 6 months ago (but disconnected ever since) and see if that solves the problem. Will also then check the charge rate of the alternator (probably leave for when you're down in a couple of weeks).

PDAS lights fine - staying on is the problem..!

Paul R · Dec 26, 2012

I was just wondering what the outcome was, ... for future reference. Or maybe the problem's ongoing.

Also to comment about the intermittent belt failure alarm - the jockey wheels wear and can cause this one. They are inexpensive and easy to change, as I recall.

Paul.

mcgc0 · Dec 28, 2012

Christmas distractions preoccupied my attention on this Paul. Now had to reprioritise with failing heating controls, and with Greg (earlier post here) we isolated the issue to the heater control unit which I now need to get something done about. All servos fine and working when tested.

The ABS/traction control light concerns are still there but seem to be behaving better in that they extinguish themselves sooner than previous. The fan belt warning light seems to only light very intermittently into a journey - sometimes not at all. Me thinks, like many in this topic, that I just need to clean up the jockey wheel connectors and check the wiring. The clock instrument itself is fine as I swapped this over a few weeks back...

Happy New Year to all...