Brakes: Another ABS thread.....

[Luxobarge]

Originally Posted by Baffler

Indeed🤞

Great write up, Luxo, and glad to read you're feeling yourself again!

Thanks mate, really appreciated. Another four trips today, and still no light, so starting to feel optimistic

[brickman]

Good write up!

The 850II app is pretty good, glad someone has bothered to take up the torch that VOL-FCR put down about a decade ago (works for most things but a little patchy). But yes hard to use and you spend a lot of time going in circles navigating around it, will get better with time i have no doubt. Kudos to the creator for getting it this far already.

Got my own ABS demon, replaced all reluctor rings and checked everything I can. Very occasionally at low speed, less than 8mph if you brake regularly, and then let off pedal and then brake with less pedal force, one of the left wheels will lock up on the ABS pump, front or rear, at random. Does it much less since changing the rings all around. Used to do it reliably each and every brake application when it has been wet under those exact conditions, new rings it now happens maybe only once a month. No ABS light and no codes ever.

Tried to run car with it on live data and getting wife to drive and vice versa but it happens so fast that Volvo 2000, VOL-FCR and OBD 850II cannot display anything fast enough.

IN every other way, brakes and ABS fine. Its just the low speed braking but not to a total stop, ease off pedal, then brake again but with LESS force = locking a wheel. However instead of every time, its now 1 in 100 times.

[Luxobarge]

@Brickman - thanks mate. Yes, agree with your comments on the OBDII app, huge thanks to the Finnish guy who's written this, not intuitive to use but it does work.

Re. your fault, given that new reluctor rings improved it so much, I'd be suspecting a poor/marginal signal from that front sensor. Sensors themselves seem pretty reliable, but I think I'd be taking it out and check that it's seated properly, fully down as far as it can go - maybe rust has moved it up a bit? Check the sensor to reluctor gap - not sure what it should be, but at least make sure it's the same on both sides.

I've done loads more journeys in mine now, and still no light, so I'm happily going to chalk this up as "fixed". That's literally as it happens, I have a chalk board with a list of car and home jobs to do, and nothing gives me more satisfaction than to wipe one from the list, especially this one as it's been there for years

Still really angry with myself for not soldering it properly the first time I had it apart though....

[duke1]

Originally Posted by brickman

Good write up!

The 850II app is pretty good, glad someone has bothered to take up the torch that VOL-FCR put down about a decade ago (works for most things but a little patchy). But yes hard to use and you spend a lot of time going in circles navigating around it, will get better with time i have no doubt. Kudos to the creator for getting it this far already.

Got my own ABS demon, replaced all reluctor rings and checked everything I can. Very occasionally at low speed, less than 8mph if you brake regularly, and then let off pedal and then brake with less pedal force, one of the left wheels will lock up on the ABS pump, front or rear, at random. Does it much less since changing the rings all around. Used to do it reliably each and every brake application when it has been wet under those exact conditions, new rings it now happens maybe only once a month. No ABS light and no codes ever.

Tried to run car with it on live data and getting wife to drive and vice versa but it happens so fast that Volvo 2000, VOL-FCR and OBD 850II cannot display anything fast enough.

IN every other way, brakes and ABS fine. Its just the low speed braking but not to a total stop, ease off pedal, then brake again but with LESS force = locking a wheel. However instead of every time, its now 1 in 100 times.

sounds exact same as mine i fixed abs so it got mot then disconnected it due to finding the fault alarming and dangerous,im told by the garage it likely has a fault in the valves that are inside the abs pump body,not brave enough to delve in there yet.
my braking was much improved by replacing all the brake fluid and giving a jolly good bleed,good luck

[Tannaton]

Finally got around to plugging mine in and it is reporting Front Left wheel sensor faulty signal - so hopefully a simple fix.

Will have a look at the weekend to see if it is a cracked ring.

[Luxobarge]

Originally Posted by Tannaton

Finally got around to plugging mine in and it is reporting Front Left wheel sensor faulty signal - so hopefully a simple fix.

Will have a look at the weekend to see if it is a cracked ring.

Interesting - IIRC it's the front left sensor that gives the engine ECU the "vehicle speed" signal and also drives the dashboard speedo. Are you seeing any odd behaviour from the speedo? If it's just the odd glitch (like it would be from a cracked/corroded ring) then it's probably not enough to see a visible change in speedo indication, but it does tell you that the sensor is not totally inactive. Check the ring/sensor gap too.

Let us know how it goes!

[Tannaton]

Originally Posted by Luxobarge

Interesting - IIRC it's the front left sensor that gives the engine ECU the "vehicle speed" signal and also drives the dashboard speedo. Are you seeing any odd behaviour from the speedo? If it's just the odd glitch (like it would be from a cracked/corroded ring) then it's probably not enough to see a visible change in speedo indication, but it does tell you that the sensor is not totally inactive. Check the ring/sensor gap too.

Let us know how it goes!

Haven't notices anything on the speedo nut haven't been looking - it did once put the EML light on with "Faulty speed signal".

[Luxobarge]

Originally Posted by Tannaton

it did once put the EML light on with "Faulty speed signal".

There you go - the actual symptoms are agreeing with the scanner, so at least you're focusing on one specific area rather than guessing. In my view you've got 3 scenarios:

1) Cracked/corroded reluctor ring.
2) Faulty sensor, or badly located in the steering knuckle
3) Bad solder joints from this sensor in the ABS unit. Pins 4 & 11 in case you're interested.

All easy enough to sort, although somewhat time consuming in the case of 1 & 3.

Cheers

[liammedler]

Is there a diagram somewhere which shows the numbers for the pins in the ABS ECU?

[volvo2]

Not sure if this is what you are after, but this is the 1995 version:

https://www.volvoclub.org.uk/tech/se...ngDiagrams.pdf

and also here (for 1994 model), on page 128:

http://www.volvo850.ru/shem/1994.pdf