Trailer ABS light

UK PROFESSIONAL DRIVERS FORUMS THE UK PROFESSIONAL DRIVERS FORUM (INTERACTIVE)
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Hi everyone, Im new here and I’m a domestic driver. Having just bought an old trailer with ABS I have encountered some of this :unamused: so I joined, to share my findings here, hope I’m doing the right thing?

VOSA and the Lamp if you’re stopped…

This is a link to what VOSA are expecting the ABS Lamps to do, I don’t think this has changed much since then.

transportoffice.gov.uk/crt/r … 063837.pdf

VOSA’s memo updating Vehicle inspectors on what action to take as a result. The chaps phone number email etc. is in there, so you could call him and get the latest on this. :laughing:

fta.co.uk/_galleries/downloa … bition.pdf

:bulb: I’m going to print these out, keep them in the cab, to “discuss” with the roadside inspectors when we meet.

Why the Lamp plays up.

From what I can tell there are 4 official generations of ABS and a further change in tractor units and the problem arises in an incompatibly in mating one generation tractor with different generation trailer. As the Vosa doc show, this doesn’t necessarily mean that the ABS isn’t functioning it perhaps shows the indication system is malfunctioning due to incompatability.

This was what my problem turned out to be…

Haldex said “Not all modern tractor units put out a voltage on Pin 6 of the 24S. If the ABS unit finds Pin 2 to work but Pin 6 not working it may set the cab light to fault.” Making it appear you trailer doesn’t have ABS, or its malfunctioning

IF you have the ISO 7638 to connect, disconnecting the 24S for a moment and seeing if the problem persists will identify the above. If so , disconnecting 2 and 6 in one end of special 24S suzie only to be used in this situation, will solve the problem. Obviously if your truck or trailer doesn’t have the ISO 7638 you cant do this or there wont be a signal at all.

You’ll see from the diagram below the signals in 24S pin 2 and 6 are duplicated in the ISO7638. Which is why Tractor manufacturers aren’t bothering now to populate the 24S pin.

This is the diagram of the 24N 24S ISO 7638 and Warning Lamp Hope this helps someone. Steve

Trailer tails.JPG
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EBS and ABS are isolated systems .ABS uses 5 wires red black yellow brown and white,the green and white and the brown and white are the can high and can low mirror signals.

When the ignition is on you should have 3 lives the red (solenoid feed) black(sensing) and brown(holding relay)

The green/white and brown/white will show a flickering digital signal for the trailer data stream.

Older trailers do not have data stream available as they use old generation 2 ECU modules and so have only 5 pins in the ISO socket connected.This "confuses "the tractor ecu as it is not recieving any data from the trailer ecu and throws up the flag.Also corroded reluctor rings will show up a fault after a time on later ecus as the digital square wave signal gets out of sync.Play in a wheel bearing(presuming you have only sensed center axle) will bring the light up after a while as well ,as reluctor signal on one side will start to “fade”

Also some older trailers have a feed to the abs through the brake lights and this can cause problems with 3rd generation tractor ecus as they detect a fluctuating voltage at the trailer ecu.

All 3 generation trailer ECUs did away with the 7 mph activation trip and do a static self test by sending a digital pulse to the wheel sensors for checking their integrity.The S susie on later tractors are only there to drive the fogs and reverse lights

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Great explanation of what is happening Bking.

Seems a bit more than a pity that the vehicle manufacturers just choose to ignore the problems rather than get on with the job of ensuring that their product is compatible with what their customers operate. They employ enough design engineers to have sorted these ongoing problems years ago.

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cav551:
Great explanation of what is happening Bking.

Seems a bit more than a pity that the vehicle manufacturers just choose to ignore the problems rather than get on with the job of ensuring that their product is compatible with what their customers operate. They employ enough design engineers to have sorted these ongoing problems years ago.

Problem is they build a nice new shiny tractor and then they programme its systems to a nice new shiny trailer.
Usual reply is “Well it works perfectly fine on our trailer”

No you numb buggers it should be built to operate with 1st,2nd,3rd generation systems thats why I bought the bloody thing.To pull all trailers not just new ones.

Had instances of EBS lockout and unlike ABS lockout which goes to standard brakes eg everything locks up,braking efficiency drops to 30% and all your left with in an emergency is the hand valve.And these people “know” how to design a brake system?

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What needs to happen is the likes of the supermarkets returning the vehicles as “unfit for purpose”.

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I’m having intermittent ABS trailer warnings this week too, it’s just road salt on the trailer wheel sensors.

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ABS fault used to be a PG9 (or GV9 as you know it) but that ceased last year. (See I did learn something on my dCPC course today hehe)

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Kerbdog:
ABS fault used to be a PG9 (or GV9 as you know it) but that ceased last year. (See I did learn something on my dCPC course today hehe)

If VOSA did a GV9 on every truck they stopped with an ABS warning when the gritters were out, there wouldn’t be any trucks left on the road apart from the gritters. :wink:

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I found this http://www.dft.gov.uk/vosa/repository/Categorisation%20of%20Defects.pdf (page 85) which says an ABS warning light is a delayed PG9. When it happens to me 70% of the time it goes out as I drive across the yard. If that doesn´t work, I´ll stop and then restart the engine with my foot on the brake. If that doesn´t work I´ll get out and try and clean the pins in the connector with a bit of tissue paper (it worked at least once). If that doesn´t work then I´ll defect it.

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I went and looked at that , Its another useful doc thanks.
The more of this collateral I have in the cab, the smaller the chance I’ll get mugged off by a road side inspector who like me, doest know what it is he should or should not be doing.

Despite the diagram I posted, its not the way my trailers wired. The connections in the Trailer sockets are not the ones down at the ABS processor or the rear lighting junction box. I ripped up the floor of my trailer today to find the hidden junction box conealed above the Fifth wheel pin. When you pull the 24S & N and ISO trailer connectors forwards the wires all look dead standard, and to the book. Little do you know a little further back there’s a junction box and there they are sharing grounds etc. going down the trailer to economise on wires. Effectively ■■■■■■■■■■■■ the standards to save a few quid.

Cheers

Steve

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bed bug:
I went and looked at that , Its another useful doc thanks.
The more of this collateral I have in the cab, the smaller the chance I’ll get mugged off by a road side inspector who like me, doest know what it is he should or should not be doing.

To be honest, I’ve always found VOSA to be entirely reasonable provided you pass the attitude test. :wink:

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I like everything working the way it should , anything for a quiet and easy life. I’ve never met VOSA out there yet, they may all be very nice and know they’re job inside out, but, I’m not taking any chances!

A wise man learns when he can , the fool…when he must.

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Kerbdog:
ABS fault used to be a PG9 (or GV9 as you know it) but that ceased last year. (See I did learn something on my dCPC course today hehe)

Well they told you a load of cobblers. Or you didn’t listen. :wink:
It hasn’t ceased. Let’s say you’re based in Preston, and you’re heading away from base, You’ll get a delayed prohibition, If you’re heading back then you won’t.

Here’s how to avoid a prohibition in the first place,
open up the dashbourd, split the clocks, and slide in a piece of black insulation tape over the ABS diode.
no more ABS light.
simples.

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We have had some new Scanias at work when I use some of our trailers I have noticed that the abs light for the trailer lights up on the dash with the warning of an abs fault. It dosen’t do it with all the trailers, it didn’t do it with the older units and sometimes it can be 30mins to an hour into the journey before it comes on, any ideas what is wrong? or is it just an incompatability problem? also what would vosa do as when I leave the yard it is fine?

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vwgpmk2:
We have had some new Scanias at work when I use some of our trailers I have noticed that the abs light for the trailer lights up on the dash with the warning of an abs fault. It dosen’t do it with all the trailers, it didn’t do it with the older units and sometimes it can be 30mins to an hour into the journey before it comes on, any ideas what is wrong? or is it just an incompatability problem? also what would vosa do as when I leave the yard it is fine?

Our Scanis do the same. Vosa saw it when I was pulled once and made me reverse up their yard, then run back down reaching 10ks to see if it went out… it did.
Don’t know why they come on, but I’m sure someone else will.

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When you couple up, try switching the unit off this sometimes helps, also try using the stowage socket for the lead when it’s not in use. This will help keep moisture out of the pins and ensure a better connection, although doing the above doesn’t always work it seems to help. Some units seem to be sensitive electronically, and will show faults when none exist.

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how old is the trailer ? we had the same problems and it was said the truck was EBS and the Trailer ABS which meant its didnt work :unamused:

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Renault Premiums did the same but with bulb warning fault on with certain trailers :confused:

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Had a Stralis where wouldn’t operate indicators, sides or brake lights if there was any more than one bulb for each one. With a trailer that had three indicator bulbs on each side you would need to take two bulbs out from each side and take all the brake light bulbs out bar one from each side. Oh happy days

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On my Stralis I get this every day when I hook up, along with license plate bulb warning but it all goes out after I brake at the first corner. :confused: