Syncro 4&4 Discussion and Q&A last answered over 2 years ago.
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After much searching I have recently bought a 1990 Caravelle GL Syncro with ABS. When I first drove it it was fine. Now when starting up the ABS light comes on and goes off as you start to move then ABS pump, under the front passenger seat, starts to whir; eventually it gives up, the pump stops and the ABS light comes on. Now I can't it through the MOT
Also the rear diff lock light comes on even if it isn't actuated. I have read a few posts in the forum re ABS woes which seem very similar. I don't have a schematic as the Bentley manual doesn't seem to cover it, none of the posts I found actually had a link to any schematics. By the looks of it the van recently has had the front left sensor changed.
Can anyone help I'd love to understand how the system was supposed to work? How to test the sensors, is there some kind of test rig that could tell if the sensor was pulsing.
disconnect sensor get the multimeter plugged in to it spin wheel whilst checking resistance ...i did have some documents pretaining to the abs system but cant find them anylonger ....might be worth giving aiden talbot a shout as im sure i sent some to him a while back...cheers
Maverick, I'm not much of a mechanic myself, but also have abs. The issue with mine was the disk that the sensor monitors gets corroded and causes an issue with the abs having a moment. It was a easy fix to clean it with a small blaster cab and painted it. Symptoms sound similar, my pump would wine then go off and the light would illuminate.
The early abs systems are not great...but do have a self diag function using flash codes I think ( golf ones do anyway, similar setup)
The pump runs for a long time to build pressure in the accumulator...it may be a duff pump or knacked accumulator..I'm no expert on the system I'm afraid and personally I would be looking to remove it if I had one fitted! My rallye has abs and it tends to lengthen stopping distances on wet roads, and hot a wet manhole over and the brakes are taken off you for a few seconds while the ancient system works out what's going on...not ideal!
Oh..and..the sensors are inductive so an AC output increasing in amplitude or summat as speed increases...a scope is the best tool to check those as the voltage output is fast and alternates between positive and negative to fast for a meter to catch..
rear difflock wiring is interconnected to ABS system, SyncroAndy was able to provide a circuit diagram when Xriss couldn't find it, it was for a customer of mine I was upgrading to difflock, in the end I couldn't wire the interlock because his seat base is welded in so couldn't get at the abs ecu connector to add the missing connection - there's a buzzer that goes off if you do more than 5km/hr (iirc) with the locker on
odd that the ecu would illuminate the difflock light - maybe an earth fault - path of least resistance
Syncro ABS wiring diagram, hope its useful. As I was pulling the wiring out of a PD130 Golf last week I was thinking to myself, how hard would it be to upgrade the ABS controller to a later model. Not something to be done lightly obviously, but if I was putting a much later engine into an ABS equipped T3 I'd certainly investigate the possibility. E D I T: Has Doug done this ? He's running T5 hubs iirc..
Syncrosport (taking a break as of summer 2024)
Volkswagen Transporter, reloaded.
ninja.turtle007 wrote:for now just remove the ABS and parking brake warning light completely from the dash pod. Should pass its MOT.
Unfortunately the MOT rules are that if the ABS is fitted it has to work. I had done as you had suggested but - removed the light in the handbrake ABS light pod blanked the front with black tape and removed the ABS relay. However the MOT guy spotted the sensors and then checked. The crazy thing is the MOT requirement is that the ABS light comes on when the ignition is on then goes off as the engine starts then stays off. If they put it on the rolling road it will come back on. They don't actually test that the ABS works.
Somebody made a suggestion of wiring the ABS light in with the alternator. I tried this with a relay but there are other electronic components there (a diode and resistors) so the circuit although it activates the relay doesn't behave as it should. My electronics knowledge is rather rusty 30 years ago at college
BTW this was only a temporary attempt as I want to getting working as it should
VW Classicparts are listing it available at 156 euros. At that price definitely worth assuring yourself its not a wiring fault you can fix instead of the pickup sensor itself. Might also be worth looking into adapting a sender off a later vehicle.
Syncrosport (taking a break as of summer 2024)
Volkswagen Transporter, reloaded.
...i did have some documents pretaining to the abs system but cant find them anylonger ....might be worth giving aiden talbot a shout as im sure i sent some to him a while back...cheers 
Thought I was on my own with my new beast