ABS not working
- Thread starter Dekker
- Start date
Neil Haughey
New member
I have had the same issue on my S2 but it seems to have gone away now. Did you find that you could still brake very hard but occasionally a wheel locked? The advice I had from my specialist which seems to have been correct is that the valves in the ABS pump got a bit sticky as the car was not being used enough. Getting the car out more and giving it some stick on track seems to have freed em back up again.
BTW can't say what it would be like on a 964 but on my S2 when the ABS had completely failed a few years back the car was almost undriveable, anything more than a prod on the peddle would cause all 4 wheels to lock on solid.
BTW can't say what it would be like on a 964 but on my S2 when the ABS had completely failed a few years back the car was almost undriveable, anything more than a prod on the peddle would cause all 4 wheels to lock on solid.
Steve Brookes
Moderator
David, a simple thing to try is, undo the battery cables at the positive terminal and shine everything up with sand paper. The ABS controller takes power direct from the battery via a tail lead that connects to the terminal. Ensuring a good contact can make a big difference to how it performs. Mine was much better after doing this.
Dekker
New member
Hi Steve,
will do regards cleaning the connections.
I'm just surprised that no indication of failure. I did alot of research before posting and read articles about how the system works and the checks that it does to verify that it's working. Yet it isn't.
See you w/e after next.
will do regards cleaning the connections.
I'm just surprised that no indication of failure. I did alot of research before posting and read articles about how the system works and the checks that it does to verify that it's working. Yet it isn't.
See you w/e after next.
Steve Brookes
Moderator
Like you, I used to get big lock ups and no warning lights or buzzers. I cleaned all the wheel sensors and got marginal improvement. Then did the battery cable and the ABS started working much better. I don't think the 964 system is particularly good compared to today's cars - I still get some minor lockups in the dry but it works really quite well in the wet, when it's needed most.
Steve Brookes
Moderator
Any progress David? Mine's completely stopped working now too! Had to do an emergency stop recently - never seen so much tyre smoke!! [
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Dekker
New member
ORIGINAL: Steve Brookes
Any progress David? Mine's completely stopped working now too! Had to do an emergency stop recently - never seen so much tyre smoke!! [
No change. I took a rear wheel off to bleed the brakes and found nipple seized so I've decided to rebuild the rear calipers and do it then. I've read a lot about the systems and will overhaul and check everything this winter when not used so much.
Let me/us know how you get on fixing it.
appletonn
New member
I had this with my old bus - check the relays that live below the cover on the ABS pump itself. 2 of them and I eliminated those first along with the power feed from the battery terminal, as Steve suggests.
All to no avail in my case, as it turned out to be the main ABS relay in the luggage compartment - try swapping that for one known to work fine and see what happens. Although, I did have the warning light and initial warning buzzer on mine when first driving off from start up, which you don't mention?
I also removed and cleaned up each of the wheel sensors, that screw into the hubs to align with the toothed rings inside.
Good luck!
All to no avail in my case, as it turned out to be the main ABS relay in the luggage compartment - try swapping that for one known to work fine and see what happens. Although, I did have the warning light and initial warning buzzer on mine when first driving off from start up, which you don't mention?
I also removed and cleaned up each of the wheel sensors, that screw into the hubs to align with the toothed rings inside.
Good luck!
Steve Brookes
Moderator
I have removed some of my own and other posts that were OT and of no relevance to subject being discussed. Apologies for the inconvenience caused.
Steve Brookes
Moderator
The bit about how you can draw a conclusion that having to do an emergency stop to avoid a dozy, impatient driver that did an overtake that was not viable, is bad driving on my part? I'll stand by my praise for the 964 brakes that even without ABS working, played a significant part in preventing that driver ploughing into my front end or worse, taking out the innocent cyclist.
In my experience those symptoms of all warnig lights operating correctly with accompaning wheel lock upon hard braking has always turned out to be the hydraulic pump/ modulator unit. As someone has suggested here already, the mechanical valve is stuck(their are several in the unit!) but the solenoid which opens it is working, so as far as the ecu is concerned it is operating correctly It is only sophisticated enough to recognise a fault at a solenoid valve electronically if the circuit is either shorted or open circuit ,anything in between is to the ecu,"plausible" and will not illuminate the light.(mechanical faults cannot be detected by the ecu as such). The ecu is also not clever enough to realise that if the wheel is not speeding back up when the valve is in operation for sometime that their must be something wrong!
The ecu upon ignition/starting does a brief check of power supplies/earths and resistance of the various components in the abs system and then a quick run of the abs pump and if that all checks out it's all systems go as far as the warning light is concerned ,in the next few meters at approx 5mph the ecu makes sure that the speed sensors are generating approximately the A/C wavefroms that it is programmed to expect under those conditions. If those conditions are not met the the warning light will illuminate and turn off the whole system reverting the driver back to conventional braking.
for instance : If the fault code wheel speed sensor left hand rear implausible signal is present, The ecu doesn't know if that is the sensor itself, the wiring between the sensor and the ecu,the ecu faulty itself , or the ring fallen off the driveshaft!! All it knows is that the data from that sensor is outside the range that it's programmed to expect. only the area of the fault can be taken for granted.
Best of luck with the fault, Cj
The ecu upon ignition/starting does a brief check of power supplies/earths and resistance of the various components in the abs system and then a quick run of the abs pump and if that all checks out it's all systems go as far as the warning light is concerned ,in the next few meters at approx 5mph the ecu makes sure that the speed sensors are generating approximately the A/C wavefroms that it is programmed to expect under those conditions. If those conditions are not met the the warning light will illuminate and turn off the whole system reverting the driver back to conventional braking.
for instance : If the fault code wheel speed sensor left hand rear implausible signal is present, The ecu doesn't know if that is the sensor itself, the wiring between the sensor and the ecu,the ecu faulty itself , or the ring fallen off the driveshaft!! All it knows is that the data from that sensor is outside the range that it's programmed to expect. only the area of the fault can be taken for granted.
Best of luck with the fault, Cj
Steve Brookes
Moderator
Thank you Colt. That is really helpful.
Steve Brookes
Moderator
OK mine is now fixed again courtesy of the boys at Unit 11, Warrington. Using a Bosch ABS tester they managed to find that the solenoid for the rear brakes in the hydraulic control unit was siezed. The only solution is to replace the unit. They sourced a good condition used one for me (a new one would have been £2.5K [:-]) and fitted it. []
If anyone else needs theirs looking at I'd suggest they contact them because the Bosch tester is the only way to isolate what the problem is and they're as rare as hen's teeth.
]If anyone else needs theirs looking at I'd suggest they contact them because the Bosch tester is the only way to isolate what the problem is and they're as rare as hen's teeth.
I had a similar problem, brakes kept locking up but no warning lights and abs light would always go out, on initial start up. With the great help from porsche Cambs and utilizing the old Bosch machine we found out that the problem was a badly squashed abs wiring loom to the wheel sensor on the off side front ! New wire and all sorted !
totyfinalist
New member
do not forget that only the 2wheel drive models require the bosch abs tester, 4wd ones use the porsche system tester one or two or piwis plus durametric and a few others!
And We have the bosch tester (c2 turbo/rs models) here in our workshop.located in wiltshire
And We have the bosch tester (c2 turbo/rs models) here in our workshop.located in wiltshire
Steve Brookes
Moderator
No mate, thanks for the compliment but my knowledge only scratches the surface when compared to folks like Mr Streather and Dave Wilkinson.
totyfinalist
New member
They are different types of diagnostic equipment used to interrogate the cars computers!
The first three being made for Porsche,(porsche system tester) pst1 (bosch kts300 hardware/porsche software), pst2(bosch kts500 hardware/porsche software) and piwis tester1(bosch kts650 hardware/porsche software) and the recently released piwis tester 2(panasonic toughbook/laptop based with siemens interface), durametric is an American aftermarket program and hardware to carry out basically the same job as the dealer tools ,without the price tag and at a somewhat more basic level in some cases on certain systems depending on the model in question.
Ok .
The first three being made for Porsche,(porsche system tester) pst1 (bosch kts300 hardware/porsche software), pst2(bosch kts500 hardware/porsche software) and piwis tester1(bosch kts650 hardware/porsche software) and the recently released piwis tester 2(panasonic toughbook/laptop based with siemens interface), durametric is an American aftermarket program and hardware to carry out basically the same job as the dealer tools ,without the price tag and at a somewhat more basic level in some cases on certain systems depending on the model in question.
Ok .
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