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ABS + PDAS warning + 16 bleeps! FIXED

Mr Bacchus

Well-known member
Joined
26 Oct 2012
Messages
303
I know there are many threads on this subject but I have not yet had any luck with my own problem so I thought I would start a thread, maybe it may help others with a similar problem. It's a bit long winded!

I am trying to fix a problem with the ABS and PDAS warning lights illuminating accompanied by 16 warning alarm bleeps! I have had this problem for approx. 18 months or so, at first it used to happen consistently but random at the point of activation i.e. at start, after driving for short while, after driving for a long while but now it happens 99% of the time as soon as I start the car.

The ABS when road tested seems to work, meaning I get the pulsing brake pedal under heavy braking. My immediate issue is that I have my MOT test due early November and this condition will result in a fail. Last November, when the problem was more intermittent, my friendly MOT tester passed the car only after he tried for a few times to get the car to run without the lamps/buzzer. I quite rightly will not be so lucky this time!

By the way, the AS book suggests wheel speed sensors or differential locks could cause these lamps to illuminate (although I have not read anything anywhere that mentions 16 bleeps!)

Here is a summary of my troubleshooting so far (in no particular order). I have relied mainly on the Adrian Streather book and Porsche workshop manuals for guidance.


- Removed, opened, examined and cleaned both accelerometers – visually okay but not yet tested as described in AS book.
- Check battery voltage at key off – 12.7 v (should be approx. 12.6 v)
- Checked battery voltage at idle – 13.85 v (should be 13.8 ~ 14.4, so on the low side)
- Bypassed relay R34 (the ABS/PDAS over-voltage protection relay)
- Cleaned the ABS control unit multi-pin connector
- Removed and cleaned the main battery earth cable connection to chassis
- Tried the 'water mist the engine bay in the dark whilst running' test to check for arcing.
- Checked and cleaned all electrical connections to ABS/PDAS components in the frunk area i.e. pump, dual solenoid valve, ABS hydraulic unit, reservoir.
- Topped up the hydraulic fluid a teeny bit (this oil has been changed annually since I bought the car) although I am sure it was fine before topping up.
- Checked all wheel speed sensor resistances at the terminals on the ABS multi-pin connector as described in the AS book – all 1000 ohms (should be 600 ~ 1600)
- Replaced both coils (I was doing this anyway)
- Replaced both dizzy caps (I was doing this anyway)\
- To the best of my knowledge no error codes present at last service in January.

Now it gets more interesting...

I discovered the left rear wheel speed sensor link-harness (from sensor connector to connector on main harness) was quite badly damaged. A replacement is £200 from OPC so I have made my own repair. The harness continuity checks out good after the repair and the wheel sensor resistance checks described above were made after the repair so in theory it should be fine but I am still suspicious of this part.

I today checked the resistance across the pins of each valve on the ABS control unit using the method described in the AS book. The resistance across pins 1 and 3 (lateral lock) should be 2 ~ 4 ohms but I measured 7 ohms. The resistance across pins 2 and 4 (longitudinal lock) should also be 2 ~ 4 ohms but I could not measure any resistance here.
Correction - I measured approx 5 ohms across these pins so assume okay. The AS book is a little misleading IMO as it shows the image of the connector on the hydraulic unit as well as the dual solenoid valve - I checked the wrong pins.

So I have two suspect components, one relating to speed sensors and one to diff locks. I can eliminate one quickly by spending £200 on a harness but I rather not if it is not necessary and the other could me much more time consuming and expensive! Maybe the I have two problems and they are multiplying up the alarm bleeps ;)

My next step, hopefully tomorrow, will be more troubleshooting of the ABS hydraulic unit valve block using the Porsche manuals very detailed procedures.

Only one question for now, does anyone know if it is possible to replace the solenoid block of the ABS hydraulic unit (assuming the relays test good) or does the whole unit need to be replaced – gulp!

Enough for now, I'm off out to celebrate my birthday.

Steve
 
Happy Birthday Steve :birthday:
Sorry to hear of your problems. To be honest I cannot help other than to sympathise. My gut tells me to brake apart the ABS box so to look for water ingress.
 
Visual and audible alarms are an indication of an electrical fault. Dependant on when the alarms appear should help identify where the problem lies. It is complicated on the C4 due to brake pressure pumps and low pressure alarms...which is where I would start first given what you have already done.

My ABS was not working but because it was hydraulic related I had no alarms. This is very common and most owners don't even know the ABS isn't working. It is nearly always because the ABS pump has seized internally. Its a fairly simple fix if a bit messy and time consuming.

BTW the ABS unit is exactly the same as found on period Mercedes 190 etc which are a fraction of the cost of Porsche units and always in better condition because of where they are mounted!
 
Chief said:
Happy Birthday Steve

Thanks! My ageometer is stuck at 52 now. Slight sore heed this morning.


ras62 said:
BTW the ABS unit is exactly the same as found on period Mercedes 190 etc which are a fraction of the cost of Porsche units and always in better condition because of where they are mounted!

That's very good to know, thanks for that!

After a blast to the coast for breakfast I'll get the tools out again and report back.
 
How long does the accumulator pump run for if you turn on ignition lights without firing the engine? If it's approaching 60s after a lay up overnight then this could be the issue.

It 'could' mean the pump/bomb is on its way out or that brake fluid has not been bled at all points including the diffs where I believe it needs Bosch hammer etc to do it properly.

This thread might be of use :dont know:

http://rennlist.com/forums/964-forum/672389-c4-brake-bleed-hydraulic-system-bleed-procedure.html

If it does relate to ABS unit I'm led to believe internal parts can be exchanged from Merc 190 units given that 964/993 ABS punps aint cheap :what: There's a thread on RL somewhere
 
Thanks for that Zingers, I'll check the pump run time tomorrow but I'm confident it does not take so long.

Some progress today after following the workshop manual troubleshooting methods (section 39/45 of the manual, volume IV).

I started the fault code 11 'lateral lock valve' troubleshooting as that is the first described. Everything checked out fine other than I do not have voltage at pins 1 and 2 of the dual solenoid valve (see correction in my first post). I moved on to fault code 34 'valve relay' as instructed.

After making all of the checks with positive results I conclude that the relay is probably broken. I partially bypassed the relay (bridged pins 87 to 30) and sure enough got the voltage at the dual solenoid valve. This relay also connects pins 87 to L1 and L2 which feed the ABS and PDAS warning lights but I didn't get a chance to build a full bridge!

I'm going to try and test the relay tomorrow at work as it could be that it is not getting the signal to energise (although all of that circuit checks out). I can also see a relay for sale on Fleabay if I need it.

I also managed to dismantle the electrical part of the ABS hydraulic unit and the only item in there than could fail is a 2.2 ohm resistor. Mine measured slightly high but I'm assuming its good for now. I'll post photos of this sooner or later for the benefit of others.

Steve
 
Would it be worth re flowing the solder in case you've got a dry joint :dont know:


Ian
 
Bacchus, I have similar issue but not great with electrics! Could you let me know what relay number or position is as May swap out to see if cure?
Boydyrs
 
Boydyrs said:
Bacchus, I have similar issue but not great with electrics! Could you let me know what relay number or position is as May swap out to see if cure?
Boydyrs

Hi Boydyrs, the relay I am investigating is mounted on the ABS hydraulic unit. If you remove the cover from this unit you will see two relays, the one I am investigating is the one nearest the center of the car and has seven pins. The ABS unit is located between your battery and accumulator. I can post some pictures tonight.

To cut a very long story short I made some progress last night in that I have proven the ABS/PDAS control unit is killing power to this relay which causes the warning lights to come on. The ABS/PDAS control unit logic is to do just that in the event of an ABS or PDAS system problem.

After extensive troubleshooting my suspicions now return to the wheel speed sensor harness that I repaired as something is telling the ABS/PDAS control unit that their is a problem and all my other tests so far are positive.

Boydyrs, from my research it seems that their are many causes to the ABS/PDAS warning light issue so I would adopt a methodical checking process. I'm not finished yet but I am learning loads and feel i'm closer.

If you want some guidance on the electrical checks then I can help. You can very quickly check this particular relay by removing it and putting 12 V over pins 85 and 86 and listening for the activation clicks. Alternatively check the resistance between these two pins with a multimeter, I measured about 50 ohms.

Steve
 
A grim day, had to cancel MOT and it expires today :nooo:

After spending all week troubleshooting including replacement of the relay I thought was dodgy I this morning replaced the wiring harness I had previously repaired (£200 from OPC). No change whatsoever other than somehow I managed to get one more warning light to come on, brake pressure. So now at engine start I have ABS/PDAS/Brake Pressure and 16 alarm bleeps. All I know is that something is killing the interlock relay to fail safe and disable the ABD and PDAS.

After even more troubleshooting today I have to assume that the ABS/PDAS controller is goosed.

I think its time to get some expert help; get the diffs bled and see what the Bosch Hammer has to say (although I have electrically troubleshot all the error codes, hence my conclusion).

If anyone with a C4 in the North East is brave enough to let me try their ABS Control Unit then I would be over the moon.

To add to todays pain its now time to watch my beloved McLaren try to qualify for the Mexican GP

Cheers
Steve
 
Spotted this on another site, it sounds similar to your issue...should be easy to check

the problem - badly tracking ignition coils and rotors. The HT supply was tracking over the insulation in the coils and rotors/distributor caps and leaking to the LT supply causing the ABS computer to have a fit!!!
 
ras62 said:
Spotted this on another site, it sounds similar to your issue...should be easy to check

the problem - badly tracking ignition coils and rotors. The HT supply was tracking over the insulation in the coils and rotors/distributor caps and leaking to the LT supply causing the ABS computer to have a fit!!!

Thanks for that information, I thought I would use that as a basis for todays troubleshooting.

Before I started today I noticed that the starter motor is dropping out after a second or two. It took me a while to start it just to get it out of the garage into the lovely sun. In the three years I have owned the car its never not started first time.

So I check all the connections between the coils and the distributors, removing the dizzy caps for a look see. All seems well without obvious signs of tracking.

I put it back together and the car is now hunting like crazy at idle, when it does run it's hunting between 200 and 1800 rpm. Went for a short drive and it struggled like hell at low rpm. Swapped DME relay just because its easy but no change.

Unfortunately I had to knock off to do some real work tonight. Tomorrow I'll check that I re-connected everything correctly on the ignition side.

Fingers crossed.
 
The hunting (if warm engine) and poor running sounds like a lambda sensor problem but strange it will just have packed up unless you fiddled with it or the connector :dont know:
 
Zingari said:
The hunting (if warm engine) and poor running sounds like a lambda sensor problem but strange it will just have packed up unless you fiddled with it or the connector :dont know:

Yep, you are most probably right. I fiddled with the lambda sensor and flywheel sensor connectors whilst I was in there yesterday.

I have disassembled and reassembled everything again tonight; unfortunately I finished a little late to run the engine as we have a baby next door and you can hear my car a street away 8)

Steve
 
Mr Bacchus said:
Yep, you are most probably right. I fiddled with the lambda sensor and flywheel sensor connectors whilst I was in there yesterday.

I have disassembled and reassembled everything again tonight; unfortunately I finished a little late to run the engine as we have a baby next door and you can hear my car a street away 8)

Steve

Haven`t you got any earplugs, you wouldn`t even hear the baby crying with those :wack:
 

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