david@st ives

I have had this problem for 4 years now.

When I start my car the pump kicks in like it should, from cold it normally takes about 40 seconds before the pump switches off, meantime the pdas and brake warning lights come on along with the warning buzzer.

When i turn the the exclaimation light off the 2 lights pdas and brake stay illuminated, after 2 or 3 presses of the brake pedal the buzzer comes back on to accompany the lights.

Now if i now turn my ignition off with the pump fully primed and turn the ignition back on all lights and warnings are off until i press my pedal a couple of times, then the lights and buzzer come back on.

Here are some observations i have made.



1 , I can get about 35 -40 presses of the brake pedal before it goes hard from a fully primed pump with ignition off.

2 , The pump comes on quite regular say after every 3 or 4 presses of the pedal.

3 , ABS works perfect

4 , central orange light comes on over bumps, hard cornering etc (Normal)

5 , PDAs does activate by central dial, Steers like a pig when activated and try to drive away

6 , Brake fluid has been changed and all the system bled including accumulator, solenoid , brakes along with longitudal and transversal locks

7, at first the lights stay on for a couple of secs then they start to flash at a steady pace approx every 2 secs /

8 , the same situation occurs with pressing the brakes whether static or on the move.

9, the same situation occurs by activating the central pdas switch without pressing the brakes

10 The same situation occurs by driving down a bumpy road

Do you think this points to a faulty pressure switch or a weak accumulator or something completely different, I did a test to see how much fluid came out of a fully charged system with ignition off but have forgotten the reading i will redo that test tommorrow.

Also there is no leaks anywhere and the fluid level is stable.

Dave

jeffnudd

I am also trying to solve this problem with Dave.

This problem that Dave has with the PDAS system is nothing like what i have found in the searches.

Any ideas would be appreciated.

Sten

Dave,

Any chance of getting the car to someone with a Bosch Hammer now that it's going again? The diagnostic codes are pretty accurate.
Other things to check:-
Is the battery/charging system OK? Low voltage can cause some strange events.
Are the connections on the PDAS control unit good? If your car was stood around in a damp garage you may have some verdigris in there. Be careful, these things are the thick end of £3000 new!
Likewise the valve and pump relays on the ABS hydraulic unit.

I've lent my copy of Adrian's book to a colleague, there's a section in there that describes what fault is associated with what combination of lights you get. maybe someone else can chime in with the info?

Good luck!

Barry

drisin80

+1 on checking the charging system. if the alternator is not putting out enough at idle (if i remember correctly it should read about 13.8 volts across the battery terminals) the pdas lights will come on. this is by design. i had a similar problem, and ended up replacing the alternator, and it solved all of my problems. tom

david@st ives

Sten

Looked in the book, first thing to look at is the pressure switch seal, (changed that last year) and the pressure switch itself.

I have always suspected the switch itself, so I have just ordered a new one (£175 from OPC).

The charging and battery are ok , I hav had this since i bought the car 4 years ago.

Will let you know how i get on, parts arrive Tuesday.

Thanks

Dave

wf758

Dave, did you check your accelerometers? My situation didn't match yours perfectly, but after dealing with similar warning light issues for 4 years...that was the key.

Good luck.

david@st ives

Will

My pressure switch is ready to be fitted before weekend , so that is my next step.

I will keep you posted.

dave

david@st ives

They say a fool and there money are soon parted.

Well theres £177 down the dain. Gutted.

According to Adrians book in Troubleshooting, in order of priority.

Pressure pump seal , ok

pressure switch , ok replaced

Hydraulic pump has failed , mine is ok

fuse 15 ok ,, relay 51 ok , .


The only thing left to check is the hydraulic accumulator.

does anyone know where i can get it tested on the car in Cornwall ?.

Also I measured my alternator charging and it was 13.6 volts.

Dave

david@st ives

ATT - C4 Owners

Can c4 owners tell me

1, what warning lights are on when they first start the car while the pump is still running ?

2 what lights remain on after the hydraulic brake pump has finished pumping ?.

dave

david@st ives

another Happy ending and another problem solved.

If only you could see me smile, I am beaming from ear to ear.

I have not felt this good since i fixed my non start problem.

Maybe Porsche will give me a job.

dave

dfinnegan

. . . perhaps you could share the fix? . . .

david@st ives

Yes I was about to.

The problem was a corroded earth wire behind the pressure switch plug.

The brown wire had totally corroded away, when i temporary made up a wire, the pump ran on for a further 10 seconds and the lights and buzzer were no more.

After my dissapointment with the replacement pressure switch i set about checking the continuity of all the wires i could find for the brakes and pdas.

I started at the pressure switch connector and only counted 4 wires when i could clearly see 5 at the loom end, so immediately knew something was amiss.

My dissapointment with the switch made me focus because there was only the accumulator to check and i knew something was stopping the switch from making the pump pressure up more.

Just goes to show Porsche have built in another failsafe mode. the pump will pressure up enough for the system to still work but not enough to extinguish the warning lights.

Dave

RicardoD

Dave,

Great job, its good you didn't have to sink more money into the problem. Its a nice feeling to have fixed a problem yourself.

wf758

Nice save

david@st ives

You would think driving my Porsche would give me the biggest smiles, but you cant replicate that feeling when you fix a long term problem.

I was like a jumping jack with the biggest smile you have ever seen when i fixed it, this has happened to me twice now.

Do you think this behaviour is normal ?.