G'day From Australia!

New to the forum? Feel free to introduce yourself / your cars. Also have a look for any frequently asked questions and information.
Post Reply
motorgnome
Knows how to use the parking brake
Posts: 141
Joined: Sun Aug 26, 2018 12:36 pm
Orga / RP numbers: Meteor Grey RP5058
Silver spares car RP4957

Re: G'day From Australia!

Post by motorgnome » Sun Dec 30, 2018 9:48 am

Next job on the list was the old "ABS out of use"...I made up a blink reader out of an old LED test light I had hanging around & pulled out the codes..
33, 34, 35, 41..All speed sensors.
I cleared the codes, checked that there were none & drove it again & they all returned.
One thing that I have noticed, is that the ECU passes it's "self test" on start up. The ABS light blinks then goes out, It is only when the car moves that the ABS light comes on....Sooooooo, in my way of thinking, the electrical connections to the sensors & the resistance of the sensors must be ok for it to pass its "self test" on start up..but, the ABS computer mustn't be happy with the signals it's receiving from the sensors when the car is moving, so it turns the fault light on.

I only had a quick physical check of the sensors/rings & clearance & the front ones look quite normal..Thoughts on this one??..Maybe the internal magnets in the sensors are no good so it is only giving a weak/erratic signal to the ECU. I have read on here they are unobtainable & impossible to remove without destroying them..something about them being glued in..well the later ones were..I suppose my best bet would be to try & see what sort of signal I am getting at the ECU. My Generic scan tool has a digital oscilliscope built into it..I have never tried it, but theres always a first hey!

I will report back & if you have seen this all before & are nodding your head going "hmmmm" ...give me some clues please!

Cheers!

Looks OK here!
IMG_20181230_183522 (450 x 600).jpg
You do not have the required permissions to view the files attached to this post.

motorgnome
Knows how to use the parking brake
Posts: 141
Joined: Sun Aug 26, 2018 12:36 pm
Orga / RP numbers: Meteor Grey RP5058
Silver spares car RP4957

Re: G'day From Australia!

Post by motorgnome » Sun Dec 30, 2018 9:53 am

Oh, whilst I was looking into my erratic interior fan blower, I pulled the one out of the silver spares car (thinking it might be the speed transistor module thing)..It was siezed up (rusty). It was only then I could see how the motor comes out of the plastic fan housing..Three rubber blocks..a bit of silicone spray & a flat screw driver & it was apart in a jiffy! You blokes must have laughed your guts out at me, when you saw the picture of me soaking the whole lot in a bath of oil to lubricate it!

citroenxm
Global Moderator
Posts: 8196
Joined: Wed Apr 15, 2009 9:11 am
Location: North Wales - FAR far far away!!! :-p

Re: G'day From Australia!

Post by citroenxm » Sun Dec 30, 2018 9:54 am

The fronts are removable with a bit of surgery.. The sensor is in a O House with a bolt. Turn the O house into a C house. Remove the bolt vola out they come.

Rears are a different story. They are completely enclosed.
the abs ring can get dry grease on them and trigger the light.. But it's wheel.. Caliper.. Disc and 6 6mm bolts to get the rear hub out with abs ring..

The other culprits are the black relay board mounted on the abs unit down in front of the gearbox on the subframe. They are A sealed box but it's been in here that they can have dry soldered joints. Cut it open carefully but essential it's sealed back up on reassembly
1990 H reg V6 24v Manual .. in progress.. on SORN
Projects:
92 L Xm 2.1t D auto project
Others
07 c5 2.2 hdi 173bhp manual

motorgnome
Knows how to use the parking brake
Posts: 141
Joined: Sun Aug 26, 2018 12:36 pm
Orga / RP numbers: Meteor Grey RP5058
Silver spares car RP4957

Re: G'day From Australia!

Post by motorgnome » Sun Dec 30, 2018 10:09 am

G'day Paul
Yes, I rear about the ABS relay board & dry soldered joints on here a while back..back when I had the front off the car doing the head gaskets. It was there looking at me, so I pulled it apart & reflowed the soldered joints, even though they looked ok..Figured it was easy then, when the car was all apart..I think it was Misha that posted that on here..I spend a fair bit of time looking..still find stuff, then can't find it again when I want to!

motorgnome
Knows how to use the parking brake
Posts: 141
Joined: Sun Aug 26, 2018 12:36 pm
Orga / RP numbers: Meteor Grey RP5058
Silver spares car RP4957

Re: G'day From Australia!

Post by motorgnome » Sun Dec 30, 2018 10:11 am

The dry grease thing might be the problem...I read somewhere on here that they only just worked when they were new, so it doesn't take much to stuff things up.

I must go & try find the pin outs of the sensors at the ecu.. It'll be on here ...somewhere!

xmexclusive
Global Moderator
Posts: 5662
Joined: Wed Apr 15, 2009 8:11 am

Re: G'day From Australia!

Post by xmexclusive » Sun Dec 30, 2018 12:41 pm

Hi Motorgnome

It might help to repeat a few of the BENDIX ABS information items in one place.

I believe that the XM Bendix ABS is a hang over from the early electronic ABS development phase.
This means it contains some features that were not replicated in later ABS systems.
It is one of few systems of that age considered to operated effectively.
Even then factory set up with new components there were reliability problems seen in service.
This led to at least 3 significant innovation changes during the production run from 1989 until 1995 when Teeves ABS took over.
The ABS rings are 48 teeth when most similar age systems were using 29 teeth.
For a given car wheel speed these extra ring teeth almost doubles the frequency at which the ABS ECU has to process signals.
This to be achieved with a slow early type of ECU microprocessor (For reference the later Teeves ECU microprocessor was 4 times faster).
That larger number of ring teeth resulted in very small air gaps between the teeth on the rear ABS rings.
This required very fast sensor signal identification by the hard pushed microprocessor.

Obsolete component item to check out and replace if found.
The earliest production XM's were fitted with Sinusoidal wide tooth rear ABS rings in the belief that it would improve signal identification.
In practice it did not achieve this and a new rotor ring with thin parallel sided teeth was introduced from RPN 5075 (1 Oct 1990).

There were some other changes made at this same date:
These comprised electrically redesigned wheel sensors and ABS ECU plus the improved assembly specification for rear sensors.

The new wheel sensors were physically identical to the originals but contained a far greater number of coil windings.
This change gives double the generated electrical pulse for a given wheel speed greatly reducing the chance of ECU error.
Early wheel sensors have a resistance between 1000 Ohms and 1400 Ohms.
These sensors are marked "Bendix F" on the along the rear of the head, that marking parallel to the cable.
The later wheel sensors have a resistance between 2200 Ohms and 3200 Ohms.
These sensors have two rows of marking across the rear of the head "Bendix F" with "SIEMENS" below.
The use of "Locktite" to glue rear sensor in place had commenced at RPN 4993.
Silicone rubber glue was used in the 9 months prior to this.

These changes were needed despite the fitting specification for XM BENDIX wheel sensors being unusually close to the rotor ring teeth.
The setting is specified at 0.5mm and new sensors were fitted with a paper shim to give the correct setting.
If we compare then the Teeves gap specification is 0.58 to 1.95mm.
Teeves sensors are non adjustable and typically come from the factory set to give a 1.2mm air gap to the rotor teeth.
This much wider air gap gives lower signal strength.
This lower signal is one of the reasons why Teeves sensors are not recommended as a direct Bendix replacement.

The XM "NEWS FLASH" system of Dealer advice notes shows that ABS sensors were giving problems and needing replacement very early on.
The mention in my index was sent out in November 1989

The later BENDIX F "SIEMENS" wheel sensors with their better signal strength added an extra ABS problem to be solved.
They were much more reliable in service but their resistance was too high for the resistance check within the original BENDIX ABS ECU.
This causes any early ABS ECU to fail the start up test if it sees a later high resistance sensor.
This puts the light on and the ABS out of use.
Citroen introduced a revised ABS ECU which could see both old and new sensors on the start up test.

Obsolete component check:
Early BENDIX ABS ECU's have a code number ending in 001. Any of these found should ideally be removed from service and destroyed.
Later BENDIX ABS ECU's have a code number ending in 002. These will work with any version XM BENDIX ABS.
There is a small physical difference in the BENDIX ABS ECU case mounting brackets on the version for Mk 2 XM's.

Bendix ABS ECU contact pins.

Top Row (pins 35 - 19)
Pin Function
35 Nearside front wheel sensor (green wire)
34 Offside rear wheel sensor (green wire)
33 Offside front wheel sensor (green wire)
32 Nearside rear wheel sensor (green wire)
31 Not used
30 Not used
29 Not used
28 Earth (yellow wire)
27 Earth (grey wire)
26 ABS light & block diode (grey wire)
25 Not used
24 Valve block coil rear brakes (green wire)
23 Not used
22 Valve block coil 1 Nearside front brake (green wire)
21 Valve block coil 2 Nearside front brake (green wire)
20 Earth (yellow wire)
19 ABS relay coil (green wire - relay is component on valve block pcb panel)

Bottom Row (pins 18 - 1)
Pin Function
18 Nearside front wheel sensor (brown wire)
17 Offside rear wheel sensor (brown wire)
16 Offside front wheel sensor (brown wire)
15 Nearside rear wheel sensor (brown wire)
14 Not used
13 Not used
12 Diagnostic socket
11 Not used
10 Not used
9 Not used
8 ABS relay coil (green wire)
7 Not used
6 Not used
5 Valve block coil 1 Offside front brake (green wire)
4 Valve block coil 2 Offside front brake (green wire)
3 Earth
2 +12volt supply, via F1 (ignition switched)
1 Not used

Note that: The +12volt feed is disconnected while the engine starter is engaged.
It is the On/Off/On sequence of this supply that initiates the ABS ECU static test.

ABS Block PCB

7 pin connector
Pin Function
1 Valve block coil rear brakes (ECU pin 24)
2 Valve block coil 1 Offside front brake (ECU pin 5)
3 Valve block coil 1 Nearside front brake (ECU pin 22)
4 Valve block coil 2 Offside front brake (ECU pin 4)
5 Valve block coil 2 Nearside front brake (ECU pin 21)
6 Not used
7 Not used

5 pin connector
Pin Function
1 +12v switched supply (ECU pin 26 & ABS light)
2 ABS relay coil feed (ECU pin 8)
3 ABS relay coil feed (ECU pin 19)
4 +12volt permanent feed to ABS relay NO contact
5 Earth ABS relay NC contact

ABS sensors.
There are now very few NOS Bendix sensors available and where offered they are usually Fronts only at very extortionate prices.
With a little mechanical machining it was possible to modify Teeves sensors for a reduced air gap fit.
The lead plugs (Blue type) needed a raised ridge removed for them to fit the (Green type) Bendix socket.
Unfortunately these Teeves XM sensors are now difficult to find available new.
There are a few recovered secondhand XM Bendix sensors to be found, mainly fronts rather than rears.
On both Bendix and Teeves ABS sensor heads there are differences between front and rear heads.
The soft iron cores are positioned longitudinally on the front heads and laterally on the rear heads.
This is done to avoid more than one ABS ring tooth being under the core at the same time.
With the wide tooth spacing on the front rings either core orientation will work.
So SOD's Law gives us rear sensors (the rare ones) that will work any where.
There are reports of fronts working as rears but BENDIX ABS history suggests there will be many reading errors and regular light on problems.

At present I have a few recovered BENDIX sensors.
I have also located a few new Teeves sensor heads which I can modify for close fit then graft on Bendix leads.
Limited time usually determines what stock holding, if any that I have.

To be continued and updated.
Version 5 (30/12/2018).

John

motorgnome
Knows how to use the parking brake
Posts: 141
Joined: Sun Aug 26, 2018 12:36 pm
Orga / RP numbers: Meteor Grey RP5058
Silver spares car RP4957

Re: G'day From Australia!

Post by motorgnome » Sun Dec 30, 2018 12:55 pm

Thanks again John. I have read through all the posts in the "ABS sensor" page in the electrical section, but you always add more information.

My plan of attack tomorrow is to try & get a visual signal via my scan tool scope, of a sensor in operation, at a set speed..Say 20kph. I will pick on one of the front wheel sensors, as they are easy to get to, but I will "scope it" from the actual ABS ecu plug, so I hopefully will be able to see what the ecu is seeing. I will then clean the ABS ring of all its surface rust (not much really) & the sensor itself, refit it with the correct air gap & check the scope pattern at the same speed to see if I have improved anything.

I will report back tomorrow on my findings
Cheers!

motorgnome
Knows how to use the parking brake
Posts: 141
Joined: Sun Aug 26, 2018 12:36 pm
Orga / RP numbers: Meteor Grey RP5058
Silver spares car RP4957

Re: G'day From Australia!

Post by motorgnome » Mon Dec 31, 2018 9:08 am

Well today was interesting..
I had the car on the ramps at work, so I dug out the ABS ECU & pulled back the connector so I could access the back of the terminals. Fired up the scope, chose the LHF wheel sensor first & ran the car on the ramps, watching the pattern produced by the LHF wheel sensor. Looked OK to be honest.
IMG_20181231_164540 (600 x 450).jpg
I was doing this when it dawned on my, that the ABS light hadn't come on...I thought "maybe there was some dodgy connection & by pulling the connector apart, Iv'e fixed it". I ran it up to 80kph & back down, still no light on. Bouyed with enthusiasm, I put the car back on the ground, cleared all the fault codes & took it for a run...Within 20 metres "bing ABS out of use!" HA!

Blink reader says all 4 wheel sensor faults..Hmm. Best I scope ALL the sensors whilst driving the car (only did the LHF on the ramps, rear wheels would be useless of course). So I went back to the LHF & tested that so I at least have a control, so to speak..then I tested the RHF..flat line...nothing...& both of the rears had a pattern, but it was so small it would be useless for the ABS computer..1/4 of the size of the pictured one (LHF)..So..at least I could see a reason for my ABS light, though I would have thought that LHF one would have been a good enough signal.

Anyway, next check was resistance..to verify what sensors I had (1100 ohms, or 2600)..I was checking these at the ABS ECU, & got to the RHF sensor & it had continuity!!! What the Hell? I disconnected the RHF wheel sensor down at the subframe & checked the sensor..1134 ohms..all good there, checked the other side of the plug & it still had continuity..That is both of the wires were touching each other somewhere!. I followed the wiring harness from the wheel sensor, along the inner wing & there was the problem.. Some nong at sometime in the cars life (probably when it had it's accident) had trapped the harness under one of the bolts that secures the charcoal canister..squashing the wires & causing the short.. I had trouble even seeing this, but I was able to shove my phone in there & take a picture..Great gadgets them phones...
IMG_20181231_180149 (1008 x 756).jpg
That's where I had to leave it..New years eve hear & we have a BBQ planned with the neighbours..

I'll keep you posted
You do not have the required permissions to view the files attached to this post.

User avatar
White Exec
Citroen God!
Posts: 5199
Joined: Fri Mar 11, 2011 7:38 pm
Orga / RP numbers: RP7165
1996 2.5TD saloon, manual, Polar White
Location: ex-Ealing, Cheshire, W.Sussex & Surrey. Now living in Sayalonga (Malaga, Spain)

Re: G'day From Australia!

Post by White Exec » Mon Dec 31, 2018 9:14 am

A really good piece of determined detective work.
Well done in locating the problem, and avoiding endless head-scratching!
Chris
1996 XM 2.5TD Exclusive RP7165 Polar White
2003 RAV4 D4D 2.0 5dr LHD Silver WORKHORSE
1989 BX19RD Delage Red Deceased; 1998 ZX 1.9D Avantage auto Triton Green Company car 1998-2001; 2001 Xantia 1.8i auto Wicked Red Company car 2001-2003

Dieselman
Global Moderator
Posts: 10940
Joined: Thu Jun 18, 2009 6:44 pm

Re: G'day From Australia!

Post by Dieselman » Mon Dec 31, 2018 9:35 am

Good diag work, there.

I suspect the ECU is seeing the imbalance of signal so shutting down.

If all sensors scope correcty then it's probably the ECU. Early Xantia Abs ECU used to fail, possibly XM ones as well.
92 2.1SED M.RP5740 ECZ Sable Phenicien
92 3.0 V6-24.Rp 5713 EXY Black
92 2.1SD M.RP 5685 ENT Blue Sideral
Prev
90 2.1SD M.RP 5049 EJV Mandarin
92 2.1SD A.RP 5698 EJV Mandarin
94 2.1SD A.RP 6218 ERT Triton Green
91 2.0SI M.RP 5187 EWT White

Post Reply