Brakes: ABS / Brake Failure light & message

[Wilse]

Hi folks, first post here and looking for some help with this D5

Car is 2005, 2.4 D5 163hp with 121k on clock

Current issue is with the ABS.

info:
ABS lamp lit
Anti Skid message

synopsis:
Abs lamp stays on constant. When moving away from starting car, speedo sticks at 20mph, revs constantly increase, no gear change (in auto)
If i switch to manual, gears change ok, but speedo still stuck at 20mph regardless of road speed.
If brake pedal depressed 3/4 times before driving, after 1 revolution of wheels, i get BRAKE FAILURE - STOP SAFELY message and BRAKE ASSIST SERVICE REQUIRED messages with red triangle. However, car then drives fine, gears change in auto OK, and speedo operates correctly

Had plugged into Vida -
Following codes presented RED

BCM-0021 Wheel Sensor, Right front faulty signal
BCM-0041 Wheel Sensor, Right rear faulty signal
BCM-0094 Communication between control units Communication problem with DEM

Amber
BCM-0042 Wheel sensor, right rear mechanical error
BCM-0109 Communication between control units communicational problems with SAS, internal fault
BCM-0031 Communication between control unitsTolerance control for SAS not run
SAS-0007 Control module internal fault
SAS-000E Steering wheel angle sensor internal fault

I have replaced the front right abs sensor, and checked reluctor rings for damage (this one recently replaced <1000mls ago, temporarily clearing ABS lamp lit)

Is it likely to be combination of 2 sensors with faulty signal causing this BRAKE FAILURE message? or is it possible its a fault with a module, given the unusual trigger for fault messages?

Any help greatly appreciated

[SwissXC90]

Physically inspect the ABS wheel sensors and reluctor rings for damage

Unplug the DEM and check connector for corrosion
Check DEM fuse
If these are OK, remove DEM, open up and inspect for corrosion

[Wilse]

Front rings look ok, cant see any obvious cracks or missing teeth. The rears are magnetic though?

this is the front ABS sensor I removed.

[Wilse]

sorry, correct image

[Wilse]

Originally Posted by SwissXC90

Physically inspect the ABS wheel sensors and reluctor rings for damage

Unplug the DEM and check connector for corrosion
Check DEM fuse
If these are OK, remove DEM, open up and inspect for corrosion

DEM connection looks fine, no corrosion on pins of connector. clean inside (forgot to take pic though!)
Fuse 7.5a (AWD #23 in rear fusebox) awkward to get to, but pulled it and is good.

Can i take the DEM off without leaking fluid though?

[SwissXC90]

If you see nothing obvious than follow the diagnostic procedure given in VIDA

An osilloscope is worth more than an entire toolbox when dealing with ABS signal issues

[Wilse]

Originally Posted by SwissXC90

If you see nothing obvious than follow the diagnostic procedure given in VIDA

I don't have access to Vida, I had the car scanned by someone with a Vida setup for the codes.

So looks like I have to change the wheel hub and rear sensor and hope for the best. Garage want £300 to do it, reckoning parts stand me around £120, might have to suck up the stripping out of the seats and hope the hub comes out without too much hassle

There seems to be a lot of ABS faults on these pages, but not many fixes?

[SwissXC90]

Originally Posted by Wilse

I don't have access to Vida, I had the car scanned by someone with a Vida setup for the codes.

So looks like I have to change the wheel hub and rear sensor and hope for the best. Garage want £300 to do it, reckoning parts stand me around £120, might have to suck up the stripping out of the seats and hope the hub comes out without too much hassle

You are guessing.
Using guesswork as a diagnostic precedure often results in replacing perfectly good parts with parts you did not need to buy, thus costing more time and money than necessary.

Example: you may have a cracked reluctor ring, but you might fit a new ABS sensor and thus not solve the problem, resulting in unnecessary costs.
Or you may have a wiring loom issue, and you only find out after fitting a new hub and new ABS sensor, again spending more than you need to.

Or it may be something completely different.


I recommend to stop guessing and start diagnosing
Diagnostics is a lot more than just a one-off code read.
It involves resetting codes, running drive cycles, reading the codes after the drive cycle, reading live data, and looking at signals on scopes and meters, sometimes deliberately inducing faults such as disconnecting sensors to observe what happens, and using other logical steps and a lot of common sense.
And that all happens before you order new parts.


But it is a free world and you are a free person who can choose to do what they want, so at the end of the day the choice is yours.

[Father Ted]

Originally Posted by SwissXC90

If you see nothing obvious than follow the diagnostic procedure given in VIDA

An osilloscope is worth more than an entire toolbox when dealing with ABS signal issues

Hi Swiss.
I suspect I have an issue with N/S front reluctor ring, not started trcing it yet as it is intermittent and (until today) hasn't caused any issues. However, today, I got the ABS warning light and Anti Skid disabled message.

I haven't read the codes yet but I do have access to a scope and think I can remember how to use one (been about 30 years!).
What would i be looking for? Would it be a voltage change as the teeth pass the sensor?

[SwissXC90]

Originally Posted by Father Ted

Hi Swiss.
I suspect I have an issue with N/S front reluctor ring, not started trcing it yet as it is intermittent and (until today) hasn't caused any issues. However, today, I got the ABS warning light and Anti Skid disabled message.

I haven't read the codes yet but I do have access to a scope and think I can remember how to use one (been about 30 years!).
What would i be looking for? Would it be a voltage change as the teeth pass the sensor?

Yes, the ABS sensor puts out pulses in time with the teeth of the reluctor ring
Not necessarily large pulse, don-t expect anything above 5V.
Maybe only a couple of volts.
But pulses that you can see.