Ok... Now my brakes have failed!!!! ABS light on, brakes don't work??? WTF?

This site contains affiliate links for which LandyZone may be compensated if you make a purchase.
Soft pedal and braking only at the end of travel means you are on the manual failsafe. There is no pressure in your system, that is clear. There are two sides or aspects to check. One is electronic, ie the pressure switch under the pump all the way up to the ABS ECU (unlikely) the other is, for want of a better word, mechanical. If there is no pressure then by process of elimination, there is a leak, there is a bleed valve open, the accumulator has failed or the pump has failed. Modulator failure is unlikely if you still have the manual failsafe working. Also as you will have read by now, it depends on the year of your car. Earlier 2 wheel TCS models had the problem, the later 4 wheel TCS ones did not.
 
Fault codes read (Thanks James!)

'ABS Pressure Warning Switch Fail'

So that's it then. Anybody know a good source for the pressure switch as a seperate item? I think LR dont list it seperately. Apparently its the exact same system as fitted to same-era Saab 9000s, and Saab list it as a seperate part - Part No 8994071. Anybody tried this before?
 
Ok - I want to test the operation of the pump and accumulator, before I start taking anything apart.

If I'm reading the RAVE wiring diagrams correctly, grounding the low-side of the ABS pump relay (RL17) coil should make the pump run and pressurise the system. The system also supposedly has a pressure relief valve, so I shouldnt be able to over-pressurise it. Doing this should charge the accumulator, make my brake pedal feel normal, and give me several full applications of brakes before the accumulator pressure is depleted, If the pump and accumulator are both serviceable.

Any thoughts? Anybody tried this before?
 
Test carried out. Partially inserted the relay, leaving enough of the terminal exposed (the thick one opposite the thin one) for me to get a crocodile clip on it. Grounded that and the pump ran. I decided to leave it running until I heard it starting to 'slow down', ie, it had reached the accumulator pre-charge pressure and was working against it. This took about 30 seconds initially - not surprising as it was the first time the system had been pressurised since I removed the accumulator. Subsequent tries took about 15-20 seconds.

Result - nice firm pedal, that survived for 10-15 applications of brake before it went soft again. I'd say from that, the accumulator and pump are working... Although perhaps a little weaker than new spec (understandable).

Only thing I need to figure out now is where to get a replacement pressure switch. Having searched I have found a few sources for the Saab part number... But they're all States-side and the switch seems pretty expensive ($325 was the cheapest!)
 
Clarky130 said:
Test carried out. Partially inserted the relay, leaving enough of the terminal exposed (the thick one opposite the thin one) for me to get a crocodile clip on it. Grounded that and the pump ran. I decided to leave it running until I heard it starting to 'slow down', ie, it had reached the accumulator pre-charge pressure and was working against it. This took about 30 seconds initially - not surprising as it was the first time the system had been pressurised since I removed the accumulator. Subsequent tries took about 15-20 seconds.

Result - nice firm pedal, that survived for 10-15 applications of brake before it went soft again. I'd say from that, the accumulator and pump are working... Although perhaps a little weaker than new spec (understandable).

Only thing I need to figure out now is where to get a replacement pressure switch. Having searched I have found a few sources for the Saab part number... But they're all States-side and the switch seems pretty expensive ($325 was the cheapest!)
Click to expand...

Good one! Try some searching, I'm pretty sure this has been covered before, I think someone may have even repaired the pressure switch. You could also try Googling Wabco pressure switches.
 
Have been doing a shedload of research about this damn pressure switch! Even looked through Wabco's own website to try and see if I could get a manufacturer's part no and source one that way... But no.

Emmetts are selling secondhand pump assemblies for £135... Even if I could source a pressure switch alone, prices I have seen mentioned in other places suggest at least £250-300 for it.

It seems the same setup (and therefore same pressure switch) is used on some Saabs and Jags, and I got a Saab part number, so may call my local Saab dealer tomorrow and see if they can get one and check price. Failing that, I think the only sensible option is to get a used one from Emmetts, strip the switch out of that and fit it to mine and hope for the best!! I'll end up with a spare pump and accumulator should the need arise (or if somebody else's pump sh*ts the bed!)

Having researched alot of info put there, it seems that the pumps themselves are pretty robust and early failure is most likely down to over-usage due to poor accumulator performance. It seems that it's considered a 'wear and tear' item, and ought to be replaced every 5 years or so... But often isn't, as symptoms of poor performance are not often seen until a pump gives up. With tha in mind, I think I'll replace my accumulator too... Mine seems to work, but 20-30 seconds to pump it up is, according to the 'pre-charge test procedure' in RAVE, quite some way outside of spec.

Once I get hold of the bits, I'll post up a 'how-to'... As well as explain in more detail the test procedure I used earlier, as I think that could be a good roadside 'get you home' fix.
 
Clarky130 said:
Have been doing a shedload of research about this damn pressure switch! Even looked through Wabco's own website to try and see if I could get a manufacturer's part no and source one that way... But no.

Emmetts are selling secondhand pump assemblies for £135... Even if I could source a pressure switch alone, prices I have seen mentioned in other places suggest at least £250-300 for it.

It seems the same setup (and therefore same pressure switch) is used on some Saabs and Jags, and I got a Saab part number, so may call my local Saab dealer tomorrow and see if they can get one and check price. Failing that, I think the only sensible option is to get a used one from Emmetts, strip the switch out of that and fit it to mine and hope for the best!! I'll end up with a spare pump and accumulator should the need arise (or if somebody else's pump sh*ts the bed!)

Having researched alot of info put there, it seems that the pumps themselves are pretty robust and early failure is most likely down to over-usage due to poor accumulator performance. It seems that it's considered a 'wear and tear' item, and ought to be replaced every 5 years or so... But often isn't, as symptoms of poor performance are not often seen until a pump gives up. With tha in mind, I think I'll replace my accumulator too... Mine seems to work, but 20-30 seconds to pump it up is, according to the 'pre-charge test procedure' in RAVE, quite some way outside of spec.

Once I get hold of the bits, I'll post up a 'how-to'... As well as explain in more detail the test procedure I used earlier, as I think that could be a good roadside 'get you home' fix.
Click to expand...

That is for checking pre charge in sphere. Under normal conditions it may take upto 40 seconds to extinguish brake lamp. That happens at 110bar.
 
wammers said:
That is for checking pre charge in sphere. Under normal conditions it may take upto 40 seconds to extinguish brake lamp. That happens at 110bar.
Click to expand...

So you reckon my accumulator is perfecty good, based on my results? I DID get up to 15 full applications of braking after 'manually' charging the system. Maybe that's about where it's meant to be and it doesn't need changing at all?
 
Clarky130 said:
So you reckon my accumulator is perfecty good, based on my results? I DID get up to 15 full applications of braking after 'manually' charging the system. Maybe that's about where it's meant to be and it doesn't need changing at all?
Click to expand...

Seems it maybe ok i don't really know. You can't do pre charge check without a pressure gauge. Idea is to note where the pressure rapidly rises to before starting to build slowly. That gives and idea of pre charge pressure if you repeat it several times. If it say goes to 40 bars very quickly then slows down and the pressure rises more slowly then charge pressure is 40 bar. If it rapidly rises to 80 bar then slows down charge pressure is 80 bars.
 
wammers said:
Seems it maybe ok i don't really know. You can't do pre charge check without a pressure gauge. Idea is to note where the pressure rapidly rises to before starting to build slowly. That gives and idea of pre charge pressure if you repeat it several times. If it say goes to 40 bars very quickly then slows down and the pressure rises more slowly then charge pressure is 40 bar. If it rapidly rises to 80 bar then slows down charge pressure is 80 bars.
Click to expand...

My thoughts on this, not having a suitable pressure gauge, were that the 'change in note' indicating that the pump was slowing down (ie having to work harder') most likely equates to the pre-charge pressure point as described in that procedure, hence why I used that to 'judge' what was going on in the system... Just a guess, might be completely wrong, but it seemed logical to me.
 
Clarky130 said:
My thoughts on this, not having a suitable pressure gauge, were that the 'change in note' indicating that the pump was slowing down (ie having to work harder') most likely equates to the pre-charge pressure point as described in that procedure, hence why I used that to 'judge' what was going on in the system... Just a guess, might be completely wrong, but it seemed logical to me.
Click to expand...

So was the note changing at 30 bars 40 bars 50 bars 60 bars 70 bars or 80 bars? You can't know with a pressure gauge. Get the new switch fitted and see what you have after that.
 
You must log in or register to reply here.

Similar threads

T
Brake troubleshooting
Replies
5
Views
466
bluedog333
bluedog333
H
MOT Failed
Replies
3
Views
721
Datatek
Datatek
Paxmanmerv
These brakes have got me scratchiung my head..
Replies
19
Views
2K
yfo866
yfo866
MikeFl4
P38A ABS faults and codes
Replies
17
Views
3K
MikeFl4
MikeFl4
M
Range Classic 1990 V8 Brake Light On
2
Replies
20
Views
2K
Madcal
M
Back
Top