ABS can signal error from pcm

[howdeedoodee]

Hi Chaps

I need some help and the story is going to take a while to get drawn up on this post in words,photo's and videos so here goes.

I've got a MK7 transit medium roof van with ABS lights coming on after driving it about a mile or two, they come on randomly and are not speed dependant as in they can come on at any random speed from 15mph to 70mph and at any random time.(max 10 minutes)
The speedo stops working and all the LCD numbers for milometer ext go to just dashes,the van also goes into a weird sort of limp mode but not a true limp mode as I can get to 70mph at any revs but the engine doesn't like it, when I turn off and back on again it drives normal until the abs comes on again, I've posted a YouTube link to show this.
https://www.youtube.com/watch?v=uLUxGzUQplI
At the start of the video it shows me doing the turn key 3 times on and off to clear engine warning light and abs light, then I drive until the fault re-occurs.
Both the batteries were replaced 6 months ago with the silver calcium ones recommended by ford.
Additionally I took both batteries out and charged up on a good £100 intelligent charger just prior to trying again.
In desperation I changed the abs sensors as some wasntt reading 1.7 ohms as listed.
I then got a reliable OBD2 code reader, the model as recommended on this forum by other members as being reliable and loaded up the For scan obd2 programme.
Whilst driving with the laptop on the dash I get kph/mph readings through live data.
However the readings are 2-3 kph different as I had two new tires fitted on the front which are 215/65 and the rears were 215/75
see video here. https://www.youtube.com/watch?v=gtDnnpC2RCk
A 60 year old mechanic who has worked on hundreds of transits doesn't think this small speed difference would create the abs error..however the For scan diagnostic code information says this could be the case??
I'm going to try some different tyres tomorrow to see if it makes a difference.
I've also traced all the wires back to the abs module to check for wire problems,wire chaffing around were they go over fuel tank ect but all seems OK.
I've checked all connectors for bad contacts and corrosion even the main cable loom that goes into the abs module.
I've cleared the relevant abs diagnostic trouble codes loads of times from the system so each time im checking with a fresh cleared DTC memory.



A few questions

As per the screen shots of the OBD2 diagnostics posted here

1.It mentions the encoder ring is damaged? Is the encoder ring the external ring you see when looking under van with the gaps all around....a bit like a cog but not pointed, I say this because I read an encoder ring can be machined within a bearing..not sure about transits.

2.I don't think i've got a worn wheel bearing as in they don't sound rough or have any play

3. Non standard accessories ?

4. I have good signal from WSS
5. Tone wheel? Is this the thing with gaps in it?6.
6. Checked damaged wires,corrosion ect.
7. its says i'm not getting a can speed signal from pcm? Where is the pcm? What can be checked?
8. I have an unrelated problem I think where I cant get 12v from the VDO to power the cargo space interior lights which is a pain in winter.....is the VDO knackered...the door locks work OK as in does the VDO get a door open signal from door lock mechanism.
9. I read a post about steering wheel angle sensor?....related to this problem or not?
10. There's an option in ABS module on for scan to reset ABS module, is this worth a try or will it reset the abs module so I have to reprogramme it? Is abs module plug and play or not?

So this is where I am with it so far, its been a bit of a brain drain but hopefully someone on here can help.
Please see both videos and 3 screenshots of the diagnostics
Thanks in advance
John the builder.

edit: when i clear the DTC (error codes) then run another scan the system is all clear of codes, then when i drive until the abs comes on the codes re-appear on a new scan.

[Punto443]

The tyres are probably the cause, as the abs unit is reading different speeds due to the size of the tyres.

The difference is exaggerated at speed, you have a invalid signal code due to the differing sizes that the van can’t make sense of, this why it’s invalid.

It’s identical to what happens when I get a flat tyre and put my 15” spare on, a few miles, lights up like a Christmas tree and drops to limp.

[knobby1]

Yep as Punto says...it's the different sized tyres causing it, they need to be exactly the same size all round or the ABS and/or traction control (if fitted) will have a hissyfit, there's a very small margin for error, exceed that tolerance and the system will not work. ...seen it many times before...and no doubt we'll see it again.

Lord Knobrot

[knobby1]

Yep as Punto says...it's the different sized tyres causing all your issues, we had a chap with this problem a week or two back. The tyres need to be exactly the same size all round or the ABS and/or traction control (if fitted) will have a hissyfit, there's a very small margin for error, exceed that tolerance and the system will not work. ...seen it many times before...and no doubt we'll see it again.

The system relies on the tyres/wheels rotating at the same RPM +or- ~1% or the system will go into meltdown and think a wheel has locked up or one is spinning faster than the others. Yours being 215/65 vs 215/75 will be ~6.3% difference in rolling diameter/circumference ...see here:

https://www.tacomaworld.com/tirecalc?ti ... -215-75r16

Lord Knobrot

[howdeedoodee]

Thanks for replies, I'm going to try tires tomorrow and I'll report back.

[howdeedoodee]

I've called the tyre place that fitted the 215x65 and hes agreed to change them so i'll report back when the tires are in for them to fit.
thanks again for replies.
John the builder,

[Aidanb]

I have had a very very similar problem but it comes and goes, seems to happen in the warmer weather.
The abs and esp lights come on, then the ------, then powertrain, then brake warning, the speedo down to 0, rpm up and down and then very rough driving, surging and very jerky.
I do have the tracking slightly off, ie the steering wheel is a few degrees off centre when driving straight ahead, this brings the esp light on after a while when driving at higher speeds.
My tyres all match.
As far as I remember I get a speed sensor fault and if I monitor it on torque on my phone it reads speed as 0 mph when driving, all other readings appear fine

[knobby1]

I have had a very very similar problem but it comes and goes, seems to happen in the warmer weather.
The abs and esp lights come on, then the ------, then powertrain, then brake warning, the speedo down to 0, rpm up and down and then very rough driving, surging and very jerky.
I do have the tracking slightly off, ie the steering wheel is a few degrees off centre when driving straight ahead, this brings the esp light on after a while when driving at higher speeds.
My tyres all match.
As far as I remember I get a speed sensor fault and if I monitor it on torque on my phone it reads speed as 0 mph when driving, all other readings appear fine

This sounds like the old "Front battery issue", is yours a FWD or RWD..?? Best to get your battery/s load tested to eliminate them.

Also might need the tracking fixed and the steering angle sensor calibrated.

Lord Knobrot

[Punto443]

I have had a very very similar problem but it comes and goes, seems to happen in the warmer weather.
The abs and esp lights come on, then the ------, then powertrain, then brake warning, the speedo down to 0, rpm up and down and then very rough driving, surging and very jerky.
I do have the tracking slightly off, ie the steering wheel is a few degrees off centre when driving straight ahead, this brings the esp light on after a while when driving at higher speeds.
My tyres all match.
As far as I remember I get a speed sensor fault and if I monitor it on torque on my phone it reads speed as 0 mph when driving, all other readings appear fine

Seen similar faults caused by the large blue/red cable attached to the engine bay fuse box being corroded.

[howdeedoodee]

Tyres being changed in a few hours..once they are done at least I can take the tyre size out of the equation, then carry on checking through the DTC check list.
however now having phoned several garages for free bit of advice over the phone they say ABS software/firmware don't allow for a nearly 8% difference between front and back wheels...its too great.
I'll report back once i had tyres changed, but thinking back this didn't happen until i had them changed.

[Aidanb]

I have had a very very similar problem but it comes and goes, seems to happen in the warmer weather.
The abs and esp lights come on, then the ------, then powertrain, then brake warning, the speedo down to 0, rpm up and down and then very rough driving, surging and very jerky.
I do have the tracking slightly off, ie the steering wheel is a few degrees off centre when driving straight ahead, this brings the esp light on after a while when driving at higher speeds.
My tyres all match.
As far as I remember I get a speed sensor fault and if I monitor it on torque on my phone it reads speed as 0 mph when driving, all other readings appear fine

This sounds like the old "Front battery issue", is yours a FWD or RWD..?? Best to get your battery/s load tested to eliminate them.

Also might need the tracking fixed and the steering angle sensor calibrated.

Lord Knobrot

I unfortunately had the problem last summer and the summer before, I did change the batteries at some point and then later on had them load tested. Had new ignition switch too.
The blue/red cable is a new one though, hadn't seen that before will have to check.
Hopefully the right tyres will sort the op, but it is just so similar to mine (my tyres match)

[howdeedoodee]

SOLVED!

I had the tires changed by the tyre place the put the wrong size on and it instantly solved the abs lights problem, ive been driving around for 2 days now and no ABS lights, before they would come on withing a few minutes
The manager of the tyre place said they have never had this problem before with transits and went on to say the it states they can put on 6 different sizes on this vehicle, i said that if you put on say 215/55 (2 sizes lower) you would be going about 35mph in a 30mph, 45 in a 40 and so on and be open to speeding camera fines.
he said well people would go to fords and have the computers recalibrated? i said who's going to go and spend £160 an hour at fords to have there vehicle recalibrated just to have a different size/wrong size tires on.
Comments please

[v8dave]

The abs only cares that all the tyres are the same size.

You could fit 215/75/13 all round and it will be happy.

But as you found fit an odd tyre or change the size on one axle and it complains.

[Punto443]

^^what Dave said

As long as all tyres match, they can be any size.

[knobby1]

The manager of the tyre place said they have never had this problem before with transits and went on to say the it states they can put on 6 different sizes on this vehicle, i said that if you put on say 215/55 (2 sizes lower) you would be going about 35mph in a 30mph, 45 in a 40 and so on and be open to speeding camera fines. Comments please

Actually, it's 'tother way round, if you fit smaller diameter tyres, the speedo will read higher than actual, so you'll be doing say 40 and your speedo will be reading 45 or possibly more depending on how small you go in diameter, so you're going slower than the speedo says.

Even with standard fitment tyres the speedo always tends to read high, my Mk7 with stock 216/75/16 tyres reads ~106kmh at an actual 100 according to my GPS, smaller diameter tyres will just make that worse.

Lord Knobrot