ABS problems - Ibiza 2008

[ACar]

So on my ibiza 2008 I have a fault code: "00287 - ABS Wheel Speed Sensor - Right Rear/ 012 - Electrical Fault in Circuit" and the ABS light is lit up and the ABS system is disabled.
A mechanic told me he is "sure its the sensor itself", so I swapped it out for a new one, on the first test drive after the swap out the ABS light was not lit for about 5-7 minutes. Earlier it always came on directly at engine start, but now again the ABS warning light comes on directly at start.

So it seems its maybe not the wheel speed sensor then. The rear right wheel shows 0 km/h at all times when measuring each wheel speed, so its not intermittently. I swapped out the ABS sensor without removing the brake calliper, and brake rotor, etc. so I haven´t looked at the sensor ring.

So what more can it be, does an ABS sensor ring break or get so dirty that it stops working completely, at all times? Or can it be a cable fault between the ABS sensor and the ABS module, even though there was a low voltage in the sensor end of the cable?
I measured the voltage at the end of the sensor cable, it showed 0.48V when ignition was turned off, and 0.11V when ignition was on (but engine off), does this voltage seem normal? or maybe that measurement is useless unless the wheel is rotating?

Any ideas would be appreciated about what can be at fault here? Thanks in advance.

 

[R3k1355]

Usually if it's not the sensor itself it's the ABS ring on the hub.

Have you checked for continuity on the sensor wiring?

 

[ACar]

Usually if it's not the sensor itself it's the ABS ring on the hub.

Have you checked for continuity on the sensor wiring?

Thanks for your answer. Now I haven't checked continuity, how is that done, do you mean to probe one end on the sensor wire and the other side of the same wire at the ABS module side?

But I measured the voltage on the sensor end of the wire, and it had a low voltage (0.11V and 0.58V), so I guess it must have continuity then?

 

[R3k1355]

Yea

Thanks for your answer. Now I haven't checked continuity, how is that done, do you mean to probe one end on the sensor wire and the other side of the same wire at the ABS module side?

But I measured the voltage on the sensor end of the wire, and it had a low voltage (0.11V and 0.58V), so I guess it must have continuity then?

Yea check continuity that way, checks for broken wires and can also check for short to ground.

Voltage does sound low, have you checked the other side to see what voltage that sensor gets?

 

[ACar]

The voltage check was in the sensor connector with the sensor removed, and 0.11V with ignition on (engine off), and 0.58V with ignition off, dont know if the sensor must be present and the wheel spinning in order to get a higher voltage, I think I read something about that online, but not sure?

Yea I could measure the voltage on one of the working sensor cables to compare.

How would one go about to check for short to ground?

My electronics skills are very limited. The sensor wire is a bit hard to follow all the way since it passes inside the car in hard to reach places.
I tried to measure the resistance on the sensor itself, but I got very conflicting numbers, so im not trusting those numbers.

 

[RUM4MO]

I checked all 4 channels on an older Bosch ABS by "looking back" up each wheel arch wiring with the power off using a high impedance multi meter on resistance mode, if in your case, all 4 look the same, and also check wrt chassis, then the wiring and the controller should be okay, in my case, it was a single channel of the controller that had failed, main dealer had not worked that out and was continually replacing sensors - it was a warranty job, so more an annoyance for me to return 6 times to get it sorted out, that was pre "good self diagnostics" era. For me, spinning each wheel and getting and AC output on a oscilloscope let me dismiss each of the wheel sensors, then, in my case, looking back up each channel wiring into the controller then confirming by unplugging the controller pinned it down to the controller. Main dealership, VX, just started at the quick and each bits first, so wasted 6 wheel sensors before replacing the controller, replacing the controller in that car, a 1991 VX Cav GSI 4X4, was as simple as opening the passenger side front door and removing a cover from the sill trim, unplug then unclick controller, then same in reverse.

Edit:- just be aware that some of these voltages might have been electrical noise and not true system voltages, that is why it is better to use a high impedance meter on resistance with the car's power off.

 

[ACar]

I checked all 4 channels on an older Bosch ABS by "looking back" up each wheel arch wiring with the power off using a high impedance multi meter on resistance mode, if in your case, all 4 look the same, and also check wrt chassis, then the wiring and the controller should be okay, in my case, it was a single channel of the controller that had failed, main dealer had not worked that out and was continually replacing sensors - it was a warranty job, so more an annoyance for me to return 6 times to get it sorted out, that was pre "good self diagnostics" era. For me, spinning each wheel and getting and AC output on a oscilloscope let me dismiss each of the wheel sensors, then, in my case, looking back up each channel wiring into the controller then confirming by unplugging the controller pinned it down to the controller. Main dealership, VX, just started at the quick and each bits first, so wasted 6 wheel sensors before replacing the controller, replacing the controller in that car, a 1991 VX Cav GSI 4X4, was as simple as opening the passenger side front door and removing a cover from the sill trim, unplug then unclick controller, then same in reverse.

Edit:- just be aware that some of these voltages might have been electrical noise and not true system voltages, that is why it is better to use a high impedance meter on resistance with the car's power off.

Interesting, okay so only one single channel on the ABS module can also break?
So I will compare the resistance with the working wheels, but a couple of questions, What counts as a high impedance multimeter? My multimeter is not a fancy one, I have 200, 2000, 20K, 200K, 20M and 200M on my multimeter on the Ohm setting.

Also excuse my ignorance, but whats "WRT chassis", I could not find anything online when searching?

And, when measuring the resistance, can I have the battery still connected, since there is a low voltage on the sensor wires even when the car is turned off, at least on the faulty side, or do I need to unplug the sensor wire from the ABS module first?

Im also curious why it took around 5-7 minutes for the ABS light to lit up only the first time after I had installed the new ABS sensor, normally it always turns on within seconds of the engine starting, and does so now again. Can some electrical fault in the car have destroyed the new sensor after a few minutes? For example if no voltage should be present in the sensor wires "at rest", but there is a low voltage?

When I think about it, in the beginning when this fault showed up, it took a bit longer for the ABS light to lit up, from 15 sec to 2 minutes.

 

[RUM4MO]

Ending up with your problem being a failure within the ABS controller hopefully is unusual, but for completeness I included that as that has happened to me.

The plan with only using a high impedance multi meter is to avoid lots of current being run down lines when checking resistance/insulation as that could damage sensitive components, unfortunately I don't know where in impedance values that term "high" begins, I only have Fluke level of quality multi meters.

WRT just means With Respect To, so test each of the 2 wires with one side of the meter connected to a good vehicle earthing point, ie clean metal on body, as well as checking between these 2 wires.

I still don't think that you are actually measuring a true potential difference at these points, it will just be an open circuit and so electrical back ground noise.

Typically with a working system, the ABS light comes on with ignition to act as a "lamp test" after the engine has been started it should go off and then within a very short distance (car moving) the ABS will perform a self test and if it detects a fault it will bring that ABS light back on.

As said by another it could be a reluctor ring issue or even a knackered wheel bearing.

Get the wiring checks done first, battery can stay connected.

 

[ACar]

Ending up with your problem being a failure within the ABS controller hopefully is unusual, but for completeness I included that as that has happened to me.

The plan with only using a high impedance multi meter is to avoid lots of current being run down lines when checking resistance/insulation as that could damage sensitive components, unfortunately I don't know where in impedance values that term "high" begins, I only have Fluke level of quality multi meters.

WRT just means With Respect To, so test each of the 2 wires with one side of the meter connected to a good vehicle earthing point, ie clean metal on body, as well as checking between these 2 wires.

I still don't think that you are actually measuring a true potential difference at these points, it will just be an open circuit and so electrical back ground noise.

Typically with a working system, the ABS light comes on with ignition to act as a "lamp test" after the engine has been started it should go off and then within a very short distance (car moving) the ABS will perform a self test and if it detects a fault it will bring that ABS light back on.

As said by another it could be a reluctor ring issue or even a knackered wheel bearing.

Get the wiring checks done first, battery can stay connected.

Thanks for your answer. So before I got an answer about the resistance test, I measured the voltage on the functioning Left rear sensor wire, and to my surprise it showed 0V when ignition was off and virtually zero with ignition on, it went up to like 0.02V with ignition on, so clearly there is a difference between the non functioning side and the functioning side.
So even if its noise there is still a difference between the two sides.

Like I mentioned earlier....I think I did, my knowledge about electronics is very limited. What does that tell you that the broken side has a voltage but not the working side? Can it be shorted to positive, or whatever its called? Could that give a voltage of 0.11V and 0.58V somehow? Earlier I measured the broken side several times and it always gave those exact numbers every time.

 

[RUM4MO]

I'd think that checking the resistance and insulation of both the working and the not working side will answer that question, ie prove if it is a broken wire or a wire shorted to something - or even a faulty controller.

The working side giving you a 0V and nearly 0v is proving that the wiring is okay and that controller channel is okay, so it is allowing a circuit to exist and keeping the voltage where it should be, a broken wire would allow you to see "voltage noise" using a high impedance meter.

 

[ACar]

Yeah so I have to check the resistance, I haven't done that yet since I'm a bit worried that some sensitive components can get destroyed on the ABS module, I guess thats why you used a high impedance meter? I read something about that being a risk if doing it the wrong way?

What I did again just to verify was to measure the voltage again, and to my surprise it measures 0.48V....with the battery disconnected, both minus and plus disconnected and yet it still shows 0.48V.
When the battery is connected and the ignition is turned on it goes down to 0.11V.

What does that indicate when its not showing 0V with the battery disconnected? So a broken wire could cause this result? And would the voltage then also go down when the ignition is turned on?

 

[RUM4MO]

It does sound like it is a wiring problem, ie a broken wire.

 

[ACar]

It does sound like it is a wiring problem, ie a broken wire.

Thanks, I will check the wiring.

 

[ACar]

Thanks for the help. So the problem was like RUM4MO suggested....a broken ABS wire on the positive side, well almost broken, it was connected with like only 2 strands of the wire (but no continuity). The break was below the rear door, so pretty easy to access, I was afraid it would be somewhere behind the dash panel. It was in a spot where it was connected to a different coloured wire, I think it was the cross over point to the interior wiring harness?.

By the way, does somebody know if there is drawings of how the wiring harnesses are routed inside the ibiza 6L? I cant find such a thing online.

 

[RUM4MO]

Good result, I don't think that there is a list of drawing showing the routing of individual cables function by function, possibly because as much as possible, all cabling will be bound up together over the longer runs.

 

[R3k1355]

By the way, does somebody know if there is drawings of how the wiring harnesses are routed inside the ibiza 6L? I cant find such a thing online.

Usually only find those in the manufacturer workshop manual, which isn't always available.

Even then the diagrams are pretty bad and just give you a general idea of where it's routed.

 

[ACar]

I had access earlier to the workshop manual and it seemed to only have the current flow diagrams, and when I looked at them I couldn't figure out how the cables are routed inside the car, I guess thats not the purpose of the current flow diagrams?

Like you said, I only got a general idea....more like from where it starts and then where it ends, but not how its routed between the start and the end.