Antiskid + Brake failure stop safely - Error expert needed!

[andyKent]

I'm not sure if this is going to be useful, but I was getting both "ABS service req'd" and "ABS temporarily disabled", progressing to "brake failure stop safely" + limp mode (2004 d5). It got bad enough that I could trigger the limp mode at will (after turning off ignition at layby to reset limp-mode) by driving up a hill and booting it (in 2nd or 3rd) - it would go into limp mode within about 2-5 seconds of putting foot down (or, if I drove gently and avoided bumps I could stave off the limp-mode indefinitely). At first I thought it was related to the engine mounts - they were all shot but I changed them all without improving my brake warnings & limp mode situation.

It turned out to be the ABS rings (both front wheels, both rusted and snapped and nolonger locked to the wheel hubs as intended).

Diagnosis is complicated by the fact that a rusted and broken ABS ring can work 'as intended' (rotate with the hub and provide pulse readings) at high speed because of centrifugal/frictional forces keeping it rotating and also complicated by the fact the ABS ring's freedom of movement is affected by the angle of the drive shafts/etc, so faults can occur when you put your foot down, or when you go over a bump. I had it happen under steady driving going over a bump/crest on the motorway, for example (which was a shock given that I was on cruise control at the time at 70ish).

My reverse-engineering-the-conservative-interpretations-of-the-Volvo-computer hypothesis on this is that when the broken (not-turning-with-wheel-hub) ABS ring in one wheel shows prolonged 'locked wheel' status (ring not moving = no more pulses) whilst the engine is under load (I.e., pretty safe for computer to assume the car is driving), you get an "ABS temporarily disabled" message and when both wheels do this at the same time, you get limp mode with "brake failure stop safely". When driving at low speed, the limp mode never came on (under 30 mph) and I just got very weird occasional ABS behaviour (no front brakes!) during low-speed-braking (and low-speed-braking-with-turns - ABS-activation-as-if-in-a-skid).

I.e., you don't need to apply the brakes to get a "brake failure stop safely" warning from the ABS rings.

After I did both ABS rings all my warnings went away and I've done >1500 miles since - no return of faults.

It's probably the cheapest thing to do on the random-diagnostic-path-of-elimination but only if you do the work yourself.

Andy

[cornerwaysuk]

My xc90 did the same, all the brake messages and abs messages. Never went in limp mode. My discs were well worn so decided to replace them and when doing this noticed that the drivers side abs ring or abducter ring was corroded and actually broken. Got the new rings (about £4 for 2 off ebay) just need to fit them.

[marzyeh]

Hi danc and all of you with this issue.
I have a XC70 2006 d5 aut with exactly the same issue.
Wonder if you or anyone solved it?

Kind Regards from Sweden

[phuz]

Has there been any solution to these issues? I am experiencing the exact same symptoms as Danc (as I know a few others are, as well). I have disconnected my DEM connector and still have the problem. I have removed my CEM a few months ago and everything looks extremely clean.

I have started a thread on Swedespeed back in July regarding this with pictures of the codes from VIDA as well as a video showing what is happening. I printed out the CAN troubleshooting guide from KBB (big thanks for that!) and intend to tackle that today.
https://forums.swedespeed.com/showth...art-(CEM-codes)

FWIW, under normal operation, my voltage would be around 14.0-14.2 (depending on ambient temp), but when the issue would occur, it would be steady at 13.5-13.6 which I have come to find out is a default alternator output when communication is lost. This morning, it was 11.5, so it wasn't charging at all. I need to look into that issue as well, because I replaced the alternator a little over a year ago. Battery was also replaced at the same time.

For now, priority is tracking down this communication problem. If anyone has a way to reach Danc, please let me know. I'd love for an update from him.

[onyourbikenate]

this thread appears to have died along with a few others with no resolution. i'm having pretty much the same issues opened a new thread here

https://www.volvoforums.org.uk/showthread.php?t=302513

if i can fix it will post the resolution. or if i roll the car off a cliff will also update the thread to state that was the resolution