ABS protection relay

citronut · Post by **citronut** » Tue Sep 15, 2009 8:16 am

can anyone tell me were to find the relay as in the title,

i know it was mentioned by someone on here a while ago that on certain year/s model's it ios under the clock tray,

i have checked and it is not under there on this one,

the car is a H reg 16V

regards malcolm

DLM · Post by **DLM** » Tue Sep 15, 2009 12:47 pm

I'm fairly sure there's a relay somewhere in the circuit, but also something I think is a diode rather than a relay.

That, if present, is in a longish, thin black plastic holder, probably swathed in insulating tape. That's what I remember being directly under the clock.

If not directly under the clock tray, I think it may be found behind the glovebox or by carefully checking cable runs that do down to the left of the clock tray.

I'd wait for someone else to confirm before pulling the box out as I recall clicking from a malfunctioning ABS circuit in the past that seemed to come from directly behind the central console.

My experience of ABS has been with 1992/3 cars - I don't know if the earlier cars had different circuits or looms.

Post by **docchevron** » Tue Sep 15, 2009 1:35 pm

Protection relay?
Do you have a part number or anything for said?
I'm sure it's in the name, but I dont recall there being a protection relay..

As DLM said, there is a diode that lives in the wiring down beneath the clock / towards the N/S of the heater box, the only relay I'm aware of for the ABS is in the fusebox..

citronut · Post by **citronut** » Tue Sep 15, 2009 6:49 pm

ok thanks
its just the CX has a relay with a diode biult in under the spare wheel rack,

and i have heard people refering to a diode and a relay regarding BX's, so i thought it might be something like the CX one,

i only know about the CX one because my CX 2.5 TRI saffari had/s one i found out after accidently conectting jump leads up the wrong way round and did not realise for a few minnuites, as the battery on the car was stone flat it did not show the usual signs of flashing, this in turn knocked out the diode in the ABS protection relay,

regards malcolm

Vanny · Post by **Vanny** » Tue Sep 15, 2009 6:50 pm

The ABS relay is ont he steering column isnt it? I dont know of a protection diode in the ABS circuit, nor a protection relay, there is a trigger relay (switched by the ignition) but thats all i know of.

citronut · Post by **citronut** » Tue Sep 15, 2009 7:05 pm

thanks Vanny also for the Sauriau

in the OE BX manual it shows a diode in circuit just after the ignition switch,

also are there diferent ABS ECU's as the sensor pin outs in the OE manual dont seem to match what the ECU plug on this car, unless im not following it corectly

regards malcolm

Post by **docchevron** » Wed Sep 16, 2009 2:05 am

Vanny wrote:The ABS relay is ont he steering column isnt it?

You're quite right.. my bad!

Citronut wrote:in the OE BX manual it shows a diode in circuit just after the ignition switch,

I've stripped the looms out of a fair few ABS BX's now, and the diode has never *quite* been in the same place, but I've never yet found one in the loom that close to the ign. switch..
Most have been under the clock, although on my valver it lives in the large nest of wiring that runs along the dash on the left hand side of the heater box by the air tube for the N/S dash heater vent..

Citronut wrote:also are there diferent ABS ECU's as the sensor pin outs in the OE manual dont seem to match what the ECU plug on this car, unless im not following it corectly

Erm, I guess it's possible, although every ECU I have here (and there's a few!) are identical, and I've never seen another type, but that isn't to say there isn't more than one..
Whats the number on the ECU you have?

citronut · Post by **citronut** » Wed Sep 16, 2009 8:04 am

docchevron1472 wrote
" but I've never yet found one in the loom that close to the ign. switch..

i dont know how close to the ignition switch it is fitted, but on in the OE manual it shows the diode in curcuit directly between the ignition switch and the ECU,

i will check the ECU ref No. in the next couple of day,

regards malcolm

DLM · Post by **DLM** » Wed Sep 16, 2009 11:00 am

I certainly know of the diode circuit feeding from the ignition through experience . I spent far too long pre-MOT one year trying to find out the reason for an ABS light that wouldn't go out sometimes, and checked my way through the Citroen diagnostic sheet without any real success.

I then proceeded to check or re-make connections, starting from the ignition feed. In the course of this I discovered the ignition switch feed was intermittent, but could be stabilised with the aid of the odd cable tie pending ignition switch/lead replacement.

You might be able to trace this feed visually with the clock-tray off. Gently move the single green(?) wire with single red connector on the centre-console end of the ignition-switch lead, and see if anything moves on the loom under the clock tray.

Vanny · Post by **Vanny** » Wed Sep 16, 2009 8:12 pm

So you did get it then, never got a reply to the PM so wasn't sure.

I by passed the relay and the diode, and stuck a switch in line to turn it off on track

Stupid bloody system. In the 20+ cars i've stripped i have never seen a different ABS ECM, but i have a stack of spares since in the history of the BX never has one failed!

The diagram in the haynes suggests the ABS is triggered by the brake light switch (god help us) and the diode is in circuit AFTER the dash light on a black wire in the anti lock braking harness. However the Job2 electrical installation has a different layout with greater information about harness coding (connectors mind) images number bx. 45-25e which matches the RWBS ABS excerpt. In that guide there is no statement of ECU pins but harness connector pins, and not something i have ever found to be innacurate.

citronut · Post by **citronut** » Wed Sep 16, 2009 8:45 pm

you are right Vanny
just goes to show how good (not)i am at auto electricary,

i was looking at the engine ECU under the drivers seat and the ABS ECU is under the passengers seat DER!!!!!!,

i have also tracked down the diode which was hidding on top of the left hand dash vent duct, and it appears to be kafut

regards malcolm

Vanny · Post by **Vanny** » Wed Sep 16, 2009 11:16 pm

I must say, i'm now intrigued as to how i have mine wired up

Hows about cut the diode out, bridge the gap, then fit a new diode in the sleeve from the ABS ECM connector, easier to work on i should imagine! And its only a coil discharge diode i imagine, not so much there for reverse polarity protection, but to stop high energy discharge.

citronut · Post by **citronut** » Sat Sep 19, 2009 9:47 am

well found the fault in the end, turned out to be the ECU i forgot the K reg BX i have on my drive has ABS, so i borowed the ECU pluged it in and bongo,

so the owner Douglas could now do with a N/S/F ABS sensor, the diode and an ABS ECU,

so dose anyone (Vanny) have all three items and how much + post to St Leonards on sea East Sussex,

or send via the FCF parts relay system

regards malcolm

Vanny · Post by **Vanny** » Sun Sep 20, 2009 7:52 pm

Appologies, only just realised this thread. I have a ABS ECM and diode you can have, pulled the diode from a valver loom today, untested at the moment, and will have an ECM in the garage.

Can you PM me your address and i'll get em in the post.