Post queries regarding your Mk3 Cavalier's ICE and electrical components (head units, wiring, retro-fit toys, upgrades etc.) here
#163403 by Telegram Sam
Fri Jul 07, 2017 1:49 pm
My ABS warning light is coming on continuously and Tech 2 (?) diagnostics doesn't appear to be able to say why. I don't have the EO something or other diagnostic plug fitted. Next step is to investigate the ABS unit directly - can anyone let me have a copy of the wiring diagram? H-reg 1990/91 / 2 litre / Pre-facelift / 8 valve / non-cat / 20 SEH.

Or is this available on the website somewhere?

#163405 by Robsey
Fri Jul 07, 2017 6:49 pm
Okay - so you are talking a very early Cavalier with 10 pin aldl (assembly line data link) connector.
The diagnostics equipment used on Cavaliers and almost all other pre-1997 vehicles was Tech 1.
The primary diagnostic language is KWP (key word protocol)

Tech 2 uses the later European "industry standard" 16 pin EOBD (Electronic On-Board Diagnostics) connector.

EOBD continued up until approx when emissions controls were tightened further, with the use of CAN (controller area network) protocol.

With CAN data stream technology came EOBD2, which uses the same connector as EOBD.
For those in the know, Petrol cars had to use CAN from late 2001. Diesels were from late 2004.

In approx 2010, this was replaced by MDI and so on...

Now then that's the techie bit.

As for your ABS - early ABS vehicles did not have on-board diagnostics, in the same way the very first injector engines did not.

So in summary - there is no diagnostics tester tool to disgnose the early ABS modules.
We have to go back to absolute basics.

So the checks are: -
Look for cracked or corroded toothed rings on the front outer CV joints.

Look for damaged or chafed wiring, especially in the front wheel wells.
Especially where tyre contact may have occured.

Finally look for corroded, damp, damaged or dirty connectors or their pins within the whole ABS circuit.

As for wiring diagram -
Look on page 224 of the pdf version of Haynes manual that I sent in Winter 2014.

You are looking for track lines 700 to 720.


#163406 by Robsey
Fri Jul 07, 2017 7:03 pm
Just for info...

If your car has ABS diagnostics, then pin K of the 10pin ALDL plug will be populated with a grey wire.

Not likely for cars manufactured before 1992. (Pre facelift models).

Using a paper clip test procedure, the ABS light on the dash will flash out number sequences if you short pins A and K together in the diagnostic ALDL plug.

These number sequences will identify the symptoms being flagged up by the ABS module.

There is a how 2 listing all the ABS error codes somewhere.

Sadly if you do not have the grey wire, then it is time to get -
a test meter to check for resistances and continuity.
oscilloscope for testing the sensor ring and pick up square wave output signal.
#163414 by Telegram Sam
Fri Jul 07, 2017 11:23 pm
Rest assured that all the above is being gratefully passed down (up) the line, tks.
You would think that this would be known to the service dept of the main Vauxhall dealeship in Newcastle but I fear that if the problem doesn't respond to Tech 2, all is lost.
For anyone following the thread I found the ABS wiring diagram on page 225 of the Haynes manual, possibly because I was using a different pdf reader.
#163416 by Robsey
Sat Jul 08, 2017 9:31 am
It was well known 25 years ago when that particular ABS system was starting to be phased out on the Cavalier.

It is likely that many of the current service personnel were either in nursery or junior school at that time.

At this point in time they would probably know as much about a Mazda 3 or some other non-Vauxhall model.
#163418 by Mk3alan
Sat Jul 08, 2017 11:38 am
Might be worth having a look at the front sensor holders, they are ally and corrode within, crushing the sensor!
One of mine did this and I had to cut the holder off the sensor and amazingly the sensor still worked although to look at it you wouldn't have thought it possible.
Later/new holders are plastic.

#163421 by Telegram Sam
Sat Jul 08, 2017 1:22 pm
Unfortunately your suggestion Alan came thro too late for this morning's investigation. All the above turned out to be to no avail cos the unit I've got is too old - no grey wires and paperclips etc. It wil be down to painstaking checking of all the connections and terminals and things, including the front sensor holders no doubt, a mega-job. Something to be thought about at the time of the re-shell ..
>> Question: Might it be feasible to "transfer" the ABS system from a 1995 N-reg LSi to my 90/91 H-reg SRi, or are the two systems just incompatible???
#163435 by Telegram Sam
Sat Jul 08, 2017 10:49 pm
I think the problem foreseen by my garage, who is very clued up as a GP but doesn't claim to be a specialist surgeon, is that the N-reg ABS would have been designed to mate with an N-reg ECU / electronic environment / braking system etc, and that you cannot just regard the ABS as a totally separate and isolated system. My understanding at least. Obviously it would make me very happy if these fears were groundless.
#163438 by Robsey
Sat Jul 08, 2017 11:52 pm
Do you know which ECU you are running?

I presume it is a 20SEH, but could be Motronic 4.1 or Motronic 1.5.

From looking at my notes, the 1988 to 1990 ECUs were Motronic 4.1.

1991 to 1993 ECU's were Motronic 1.5.

Now then - I am running a 1992 to 1995 ABS 2E module with a 1991 to 1993 Motronic 1.5 Engine ECU.
Both work fine together.

There is no direct communication between the engine ECU and the ABS 2E module.

There is the standard diagnostic brown and white wire, between the ABS 2E module and Engine ECU.
but even the earlier 4.1 ECU will have the brown and white wire that you can link up to, if required.

So as I said - the later ABS 2E module should be successfully transferrable to an older car model. Especially if you have the 1.5 ECU.

Your garage is looking way too deep into this.
#163439 by Robsey
Sun Jul 09, 2017 12:09 am
Personally, I would look at repairing your existing set up, rather than going into attempting the unknown.

A sensor, CV joint or a sensor mount will be a lot cheaper and easier to replace, rather than a complete system upgrade, just so that you can do diagnostics.
#163440 by Telegram Sam
Sun Jul 09, 2017 12:24 am
RE part 1: Looks like mine could be borderline 20SEH / Motronic 4.1 / 1.5. (I took delivery in Jan 91, I can remember).
- can I deduce which?
- does it matter?
- I may have slightly misquoted my garage man
RE part 2:
- he seemed to think that checking all the connections etc would be a laborious job whilst with the prospect of "merging" the H reg and the N-reg it would not be such a major job to include the ABS in the transfer also. Not that transferring would exclude checking the connections in the first place. I suppose that the ABS itself might have failed. I'll pass on your comments.
#163441 by Robsey
Sun Jul 09, 2017 12:39 am
The ABS modules themselves are quite robust.

99.99% of failures are due to everything else.
Pulse pick up sensors,
ABS toothed rings on the CV joint,
Dirty or corroded connectors.
Damaged wiring in the front wheel arches,
And unknown to me - corroded sensor mounts.

So nothing too difficult if you know what to look for.

As per your updated quote -
Fitting an updated system would indeed be a lengthy involved process.
(Labour intensive to use your words).

I am not sure if the early ABS brake line split is the same or different to the later brake line configuratiom.

By that I mean -
Diagonal split - front left is linked to rear right, and front right is linked to rear left.
Or ...
Front / rear split -
Both fronts are linked and both rears are linked.

If there is a difference, then that would incur a whole load of additional plumbing.

As said - so much easier to repair what you have already.
#163455 by Tobias_CDX
Sun Jul 09, 2017 1:46 pm
You got the old ABS system with its ECU installed at the seat called "ABS 2S". This system has no diagnostic function. Maybe you find someone who still has a KM-566 diagnostic unit. This will do the search for errors a lot more easier.


If you haven't there is some measuring to do. Remove ABS ECU and check direct at connector voltages of power supply and ground connection. Inner resistance of wheel sensors shall be 0.9 to 1.3 kOhm. Insulating resistance of wheel sensor shall be greater than 100 kOhm. Change of voltage at sensor shall be greater than 100 mV if wheel is spinned at one rev per second. Common ABS errors are the sensor or connection of the sensors.

Later systems "2E" and "2EH" with ECU installed at hydraulic unit have diagnostic function.
#163456 by Telegram Sam
Sun Jul 09, 2017 2:41 pm
Many thanks - I will pass the info on (!). If anyone has a KM-566 that they'd be prepared to loan me I would much appreciate.
#163457 by Mk3alan
Sun Jul 09, 2017 6:39 pm
Still got to jack it up and spin the wheels though!
The sensor output can be checked at the abs ECU plug as this will then include all the cabling and connectors. If no output is found it can then be tracked back down the relavent wiring until the problem is found.
It would be worth giving any plugs/connectors you take apart a squirt of contact cleaner/lubricant (Servisol recommended)

#163461 by Robsey
Mon Jul 10, 2017 8:27 am
I am sure that there is likely to be next to nobody in a domestic situation with any of the Kent-Moore test tools.

And after 20-odd years not many garages either.
You best chance is a really old skool independent Vauxhall Opel specialist garage.
#163502 by Telegram Sam
Sat Jul 15, 2017 10:48 pm
I tracked down such a gentleman in a back street garage in a posh residential part of Newcastle. Whether he had a Tech 1 or its predecessor he didn't say but fairly quickly he was able to pinpoint a trapped / squashed ABS cable. Obvious enough when you looked at it. I got this repaired but unfortunately the ABS light is still on. But we then identified a broken ABS sensor mounting bracket at the front n/s wheel and it seems that this part no 90345826 (now in plastic) is actually in stock at the main stockists. Hope lives on ...
#163510 by Robsey
Sun Jul 16, 2017 1:32 am
I don't think it would.
I think you need to use a basic test meter to check resistances and voltages through the relevant wires,
And an oscilloscope to test the abs sensor outputs

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