ABS air gap nightmare W639 Vito.

[GranTouringRacing]

Hi i have a 2012 W639 vito 116cdi RWD and it is my distinctive work van i replaced everything as i wanted it a reliable work van, new Bilstein suspension, Big brake conversion, uprated everything, custom exhaust, new bushes, new propshaft, new bearings, the whole shooting match.

My problem lies in the rear abs sensors, like i said all new bearings, sensors, discs and pads, everything was great and then i had limp mode as both rear sensors were reading speed but had the air gap fault, i realised i had bought generic cables so bought another full set from the autofactors, I then got rid of limp mode but the fault is just rear left with the same fault, air gap!

In my 20 years as a mechanic i have never had this problem on a vehicle with a simple hole and bolt sensor.

Is this a common issue, i know i’m being told to go genuine by many people but the fact the right hand side works now but not the left makes me think its something else?

£300 quid for genuine cables when it may not fix the problem seems like a crap gamble to me?

I use the same brand cables for all makes and never get this problem, could i have another issue here or is the gap such a small finite reading on these?

Would a voltage drop, crappy connection do this?

DTC fault code i have is:

44A8

Thats on the icarsoft MBII scanner i’ll put it in Xentry later to see if i get another code?

Also is there a way to delete the brake wear sensor other than cutting and joinjng the wires, my front brakes are 358mm 8 pots so do not have the standard brakes, I can’t see anything on Xentry that can switch them off, is there a fuse i can pull to stop the warning light or is it ‘old skool’ join the wires?

Thanks in advance people!
Scott.
Gran Touring Racing
GTR REMAP LTD.

 

[GranTouringRacing]

Did anyone ever read this?

 

[Jobsworth]

I’ve had trouble with aftermarket sensors on the rear of Vito before. If you have the ability to read live data while you drive that might pin it down. In my experience the aftermarket sensors read exactly double the road speed

 

[GranTouringRacing]

I’ve had trouble with aftermarket sensors on the rear of Vito before. If you have the ability to read live data while you drive that might pin it down. In my experience the aftermarket sensors read exactly double the road speed

I have Xentry and icarsoft, the weird thing is they seem to all be reading fine yet this air gap issue is the only problem!

 

[Nicebutdim]

Just a thought. Don’t know if it‘s same on your vehicle but on my W211 front bearings when you install the bearing seal (which is also the magnetic reluctor ring) you need to take care not to press it into the housing too far. Pressing it in too far increases the air gap between the reluctor ring and sensor.

 

[GranTouringRacing]

Just a thought. Don’t know if it‘s same on your vehicle but on my W211 front bearings when you install the bearing seal (which is also the magnetic reluctor ring) you need to take care not to press it into the housing too far. Pressing it in too far increases the air gap between the reluctor ring and sensor.

Yeah these were a one piece bearing and seals with sided magnetic strip, whats getting me is both sides didn’t work on the first set of cables, then the second set from Euro Crap Parts the right side works, so I’m guessing it is cables but surely they can’t be that different its just a hall effect sensor, i reckon its a wiggle and a tighten before i shell out for MB ones, i wish i hadn’t done them now as they were all fine, i just thought i’d renew with the build as it was all stripped!

I suppose i should stick to the old adage, “if it aint broke, don’t fix it!”

 

[Bellow]

I have Xentry and icarsoft, the weird thing is they seem to all be reading fine yet this air gap issue is the only problem!

Who or what is defining this 'air gap issue'?
You say they are all reading fine - so implies the air gap is correct (or there'd be no readings). Or is that your diagnostics reading that the sensors are there (present) - not live (output) data with a wheel rotating?

 

[GranTouringRacing]

Who or what is defining this 'air gap issue'?
You say they are all reading fine - so implies the air gap is correct (or there'd be no readings). Or is that your diagnostics reading that the sensors are there (present) - not live (output) data with a wheel rotating?

Live data of the speeds is reading each wheel with a speed.

However the fault code states wheel gap, the icarsoft checks this as a live data field and the Xentry shows it as a fault code, as soon as the van moves the lights come on the dash and stay on!

I cant post pictures from my phone as it says the files are too large?

 

[GranTouringRacing]

Live data of the speeds is reading each wheel with a speed.

However the fault code states wheel gap, the icarsoft checks this as a live data field and the Xentry shows it as a fault code, as soon as the van moves the lights come on the dash and stay on!

I cant post pictures from my phone as it says the files are too large?

44A8 Component L6/3 (Rear left RPM sensor) does not function properly (speed sensor at left rear axle has a gap)

 

[Bellow]

Live data of the speeds is reading each wheel with a speed.

So no accurate output? Any output?

However the fault code states wheel gap, the icarsoft checks this as a live data field and the Xentry shows it as a fault code, as soon as the van moves the lights come on the dash and stay on!

Which I read as circuitery OK, no or invalid output from sensor.

I cant post pictures from my phone as it says the files are too large?

Cropping (if possible) sometimes works.

 

[Bellow]

44A8 Component L6/3 (Rear left RPM sensor) does not function properly (speed sensor at left rear axle has a gap)

Can you swap sensors side to side and see if the problem shifts sides?

 

[GranTouringRacing]

Can you swap sensors side to side and see if the problem shifts sides?

Possibly but I actually had this fault on both sides with the first set of cables, but when it was on both sides it went into limp mode, so my worry is, if it goes onto both again after a swap I can’t use the van!

I will play about with them and see if there is any adjustments to be made the fact the right appears to have fixed itself with the new cables but not the left is baffling!

although the left does have twin cables with the brake wear sensor also so the actually different!

 

[Bellow]

My problem lies in the rear abs sensors, like i said all new bearings, sensors, discs and pads, everything was great and then i had limp mode as both rear sensors were reading speed but had the air gap fault, i realised i had bought generic cables so bought another full set from the autofactors, I then got rid of limp mode but the fault is just rear left with the same fault, air gap!

This is what I don't understand - how it can give readings and have an air gap problem. If the air gap is too large, not enough signal to give a reading - or so I thought.
Maybe, (guessing here) limp mode was because there was a (perceived) problem on both driven wheels (ESP, TC concerns)?

I use the same brand cables for all makes and never get this problem, could i have another issue here or is the gap such a small finite reading on these?

Is the air gap measured or measurable? How could there be a consistent value when the sensor could be sitting over a tooth or between teeth? That it appears (as light on the dash) as soon as all 4 wheels are rolling makes sense though as an air gap problem - but not getting readings of wheel speed. Unless....

Would a voltage drop, crappy connection do this?

....the signal is getting lost due to the above.

If there are any errors in the above as to how I'm reading what's going on - please correct me.

Going slightly leftfield..... saw a guy having an 'air gap issue' with a crank position sensor. The fault was eventually traced to the reluctor wheel not turning with the crankshaft, just sitting there as the crank spun...

 

[Nicebutdim]

When i was having similar problems i read that some aftermarket bearing sets had an inadequate chamfer for the axle on the bearing. Again this pushed the reluctor away from the sensor.

the guy who posted this info solved it by some judicious grinding. The thread might be on this forum, you’ll have to do a search.

 

[GranTouringRacing]

This is what I don't understand - how it can give readings and have an air gap problem. If the air gap is too large, not enough signal to give a reading - or so I thought.
Maybe, (guessing here) limp mode was because there was a (perceived) problem on both driven wheels (ESP, TC concerns)?

Is the air gap measured or measurable? How could there be a consistent value when the sensor could be sitting over a tooth or between teeth? That it appears (as light on the dash) as soon as all 4 wheels are rolling makes sense though as an air gap problem - but not getting readings of wheel speed. Unless....

....the signal is getting lost due to the above.

If there are any errors in the above as to how I'm reading what's going on - please correct me.

Going slightly leftfield..... saw a guy having an 'air gap issue' with a crank position sensor. The fault was eventually traced to the reluctor wheel not turning with the crankshaft, just sitting there as the crank spun...

Bellow,

As a mechanic that does diagnostics this is baffling me also!

There isn’t any adjustment in anything, its a hole with a bolt hole, the bearings can only go in as far as they will go home and a circlip fitted!

The hubs go in as far as they can go, the driveshafts are splined so can’t spin and the pick up is on the bearings.

The fact with the cheap cables they both didn’t read, then I bought cables from the autofactors and one side works absolutely fine, same shape sensor, same hole that it goes in but now it works without a gap?

I had a BMW X5 that had an airgap fault but it was about 2kmh out which sent the engine management daft, this turned out to be a warped hub carrier! However the Vito brakes worked absolutely fine, the original bearings and sensors taken out replaced with new and then didn’t work, more new cables and one side works, so just like you, i’m baffled, i’ll maybe see if i can use my autel or the snapon verdict to see if i can graph the speeds, but on a visual live data all wheels seem to be fairly coherent and constant?

Limp mode occurred because there was a fault on 2 axles of the same axis (both rear) so as a coherent speed couldn’t be produced on an opposite side as a safety net i assume thats why limp was implemented?

Could a faulty former cable blow a fuse? The fact the cables have power and do take a reading suggests this isn’t the case?

Hence why i’m here asking if its maybe a voltage thing? Could the connectors cause a voltage drop that flags up an air gap? These sensors usually use a 5v system?

In which case i’m tempted to hard wire the cables or get new connections?

I just cannot believe it is in the branding of the cables personally, or the company that makes them surely would always have this problem for every Mercedes, the auto-factors would very quickly stop supplying them if they kept being returned?

I’m going to do a strip and clean before i change anything after i try and get some live data?

Is there a way to upload videos in here if i can pull a live data graph?

The brake pad wear sensor on the side that has a gap doesn’t work either, when it did before, is there a way to program out brake pad warning without bridging the wires (the front has huge 8 pot calipers with 358mm discs so is bridged anyway?

Surely this wouldn’t cause an ABS issue tho?

 

[Larkone]

The brake pad wear sensor on the side that has a gap doesn’t work either, when it did before,

Two electrical errors on the same side - possible SAM issue?

 

[Jobsworth]

The brake pad wear sensor on the side that has a gap doesn’t work either, when it did before,

Two electrical errors on the same side - possible SAM issue?

Not got the two plugs at the inner end of the cable muddled up?

 

[Nicebutdim]

A dodgy connection or a faulty magnet could cause a flaky signal flagging up an air gap fault.

In my case an air gap fault on one side was sufficient to put car into limp mode at speeds above 10mph. i had a damaged magnet. Replacement of the magnet solved the problem.

 

[Bellow]

Bellow,

As a mechanic that does diagnostics this is baffling me also!

There isn’t any adjustment in anything, its a hole with a bolt hole, the bearings can only go in as far as they will go home and a circlip fitted!

I would - just for peace of mind - check the (inserted) length of the two sensors against each other just in case there's been a manufacturing fault on one ( unlikely though that is). Swapping them would be another check. Finally, a bit of Blue Tak to check what clearance exists.

The fact with the cheap cables they both didn’t read, then I bought cables from the autofactors and one side works absolutely fine, same shape sensor, same hole that it goes in but now it works without a gap?

Possibly a clue there. There's some suggestions from other contributors regarding this.

I had a BMW X5 that had an airgap fault but it was about 2kmh out which sent the engine management daft, this turned out to be a warped hub carrier! However the Vito brakes worked absolutely fine, the original bearings and sensors taken out replaced with new and then didn’t work, more new cables and one side works, so just like you, i’m baffled, i’ll maybe see if i can use my autel or the snapon verdict to see if i can graph the speeds, but on a visual live data all wheels seem to be fairly coherent and constant?

Can we firm up the terminology here?
Diagnostics recognising the presence of sensors - which implies good sensors and wiring.
Live data from sensors - ie, when wheels are turning, verifying output signals from the sensor.
At a guess, it should be possible to detect an (flickering) output from a sensor on a multi meter directly connected and the wheel spun by hand.

Limp mode occurred because there was a fault on 2 axles of the same axis (both rear) so as a coherent speed couldn’t be produced on an opposite side as a safety net i assume thats why limp was implemented?

I'm guessing that's the case. There would have been no verification of gearbox output speed.

Could a faulty former cable blow a fuse? The fact the cables have power and do take a reading suggests this isn’t the case?

Hence why i’m here asking if its maybe a voltage thing? Could the connectors cause a voltage drop that flags up an air gap? These sensors usually use a 5v system?

No, except for the complication of the wear sensor which I'd guess is fused. The sensor outputs are only present when the wheels are turning, and so low a current as to not require fuses.

In which case i’m tempted to hard wire the cables or get new connections?

Not sure what you mean by that? Try to 'jump' them?

I just cannot believe it is in the branding of the cables personally, or the company that makes them surely would always have this problem for every Mercedes, the auto-factors would very quickly stop supplying them if they kept being returned?

Quality control isn't everything it could be. If the cable are as simple as I imagine them - can they be interrogated with a multimeter for resistance/continuity? I'd expect any problem there to flag as 'lost connection' and/or 'faulty sensor' not 'air gap'. But you've been here already with the one that cured one side.

I’m going to do a strip and clean before i change anything after i try and get some live data?

See previous request.

Is there a way to upload videos in here if i can pull a live data graph?

I don't know how to - but vids are possible.

The brake pad wear sensor on the side that has a gap doesn’t work either, when it did before, is there a way to program out brake pad warning without bridging the wires (the front has huge 8 pot calipers with 358mm discs so is bridged anyway?

Surely this wouldn’t cause an ABS issue tho?

Another clue to crossed wiring (or similar) between ABS and pad warning system?

Another leftfield suggestion - brake switches can create weird ABS issues. That the braking lights are working isn't enough verification of switch as they frequently have two contact sets. One for lights, the other for ABS, etc. For the time it takes to check....

 

[Fazzy2005]

Hi did you manage to sort this?
I have abs and traction light on fault relates to o/s/r air gap changed the bearing 2 times and speed sensor all from dealer but still get this when turning the ignition off light goes out and only comes on when wheel rotates
Anyone that can help