ABS fault

[DIYspanner]

2004 Bora TDI

Like my 2003 Bora TDI, I plugged my new Topdon scanner in to fault find.

With the 2003, it reported a rear sensor which I replaced and that switch off the triangle and abs lights.

With the 2004 I'm now doing, the warning triangle is lit and the abs is flickering as soon as the ign is switched on. They both stay lit with the engine running.

I did a scan which reported the front right wheel sensor which I replaced yet the warnings are still lit.
The abs sensor is just under 1k ohms and the cable voltage from the harness is 2.3v, both which I believe are the right valves.

Would I be correct in presuming it may be a abs module error?
Anyone had this bother?

 

[Burnerman]

Did you check the reluctor ring on that side?
Very prone to rust, cracking or even falling off.
John

 

[carmanmemoranda]

Be wary of replacing items just because a code is set.

I'd agree with burnerman, have a good look at the reluctor ring, or even corrosion pushing the existing sensor away

 

[DIYspanner]

The hub, inc reluctor ring, was replaced four years ago due actual damage to the old ring. I checked it whilst doing the sensor.

Its the fact that the abs warning is flickering that bothers me.

 

[carmanmemoranda]

What code(s) did you get ?

 

[Belle427]

Live data is handy for monitoring the wheel speeds if you can get into it.

 

[DIYspanner]

The code is 00285

 

[carmanmemoranda]

From memory, I think the front sensors are identical, not handed ?

Swap left to right , delete codes, and see what code shows then ? Either it changes wheel, so suspect the sensor, or it stays the same, suspect wiring or other ?

What brand did you fit? Cheapy or good quality ?

 

[DIYspanner]

From memory, I think the front sensors are identical, not handed ?

Swap left to right , delete codes, and see what code shows then ? Either it changes wheel, so suspect the sensor, or it stays the same, suspect wiring or other ?

What brand did you fit? Cheapy or good quality ?

Sadly the front sensors are handed.

I fitted an Apec brand sensor and although now owned by NAPA, presumably still a quality parts source?

Apec part no ABS1005 front right and ABS1004 front left.

 

[Harry Bloomfield]

ABS systems, run a couple of diagnostics...

1. When the ignition is switched on, to check the ABS module, and the wheel sensor appear to be working. The static test.

2. When the car moves, to ensure each sensor is producing the expected pulse signals. The on the road, continuous test.

I've only once had ABS problems, long ago, on a Granada. It was intermittently turning the warning light on. That used a coil type sensor. I resolved that by diagnosing which corner, and found it was due to oxidation in the plug pins. A spray of WD40, cured it.

Latest car, uses Hall Effect sensors. In the boy scout tradition, I dived in with no faults, to see how easy that might be to diagnose and fix. I found I could detect the pulses from the Hall Effect, with an LED oscilloscope, I then later found I could also detect the pulses, with a piezo earphone, so I made up a break out plug and socket, which could be quickly plugged into the loom, between sensor, and the ABS loom. I have yet to need to use it, but it's there should I need it...

Aside from the sensor failure, or module failure, they can suffer from rust attaching itself to the reluctor ring, disturbing the pulses. So I devised a way to test for that, using the piezo earpiece.....

Wheel jacked up, ignition on, and earpiece listening to the clicks. Add a pointer close to the tyre, and some chalk. Rotate the wheel slowly, and each time you hear the click, mark the tyre. The marks should end up, perfectly evenly spaced around the tyre, and the correct number - from memory, mine should produce 49 pulses, per full revolution.

Back to the OP's problem - Intermittent flickering on and off, whilst moving, suggests, a poor connection, something similar to what my Granada suffered. It should be logged in the diagnostics, but most likely a problem at the sensor to loom plug and socket, close to each wheel.

 

[baldykev]

what did you use to measure the volts at sensor, if it was a multimeter it might be better to try a bulb that way you are putting a load on the circuit that will show up any bad connections/broken wires .multimeter has a high impendence and will put the circuit under load.

 

[carmanmemoranda]

Sadly the front sensors are handed.

I fitted an Apec brand sensor and although now owned by NAPA, presumably still a quality parts source?

Apec part no ABS1005 front right and ABS1004 front left.

Id fit a quality part before going further.

Cheap aftermarket sensors are a total waste of time money and effort.

May not be the sensor, but.

Remove the connection from the other side and see what code(s) that flags up

 

[DIYspanner]

I fitted an Apec brand rear sensor to my own Bora TDI last week and that put the abs light out.

With the one I'm on with now, I swapped the Apec sensor for a Delphi brand - the problem persists.

I've checked both side cables off the battery terminals, live to - and ground to +. The reading were identical.

I starting to think the abs module is the culprit.

I used my new Topdon scanner to graph the front n/s and both rear sensors when driving. The graph curves were near identical.

I then graphed the both front together. This graph is the output. The RHS is very jumpy.

 

[johnny2007]

ABS module.
I had the same problem on my Passat and it turned out the ABS module has some super-thin wires soldered to the board.
These get dislodged and sometimes are close enough to make slight contact giving you the warning light flickering effect.
You can check by removing and opening the module; it takes minutes.
If that's the problem, get an original one from ebay.
The same module was used up to the b6 VW version of Bora/Passat.