406 phase 1 Brake question

[moizeau]

Right then. Set off Wednesday in the 2.1td, fully packed up to do a 500 mile round trip to Lyon to take my son to his new engineering college. 30 miles into the journey, at a junction my brake pedal went gradually to the floor, released the pedal, re-applied, car stopped. I have an intermittent fault on the abs so I wondered if it was that. Next junction same again, s**t! Got out to see a drip coming from the rear right in between the wishbone and the fuel tank. Turned round and came home (very gently) using the handbrake and gears so as not to force more fluid out of the system. Luckily to route was across country. By the time we got home the light had come on permanently. I'm just about to put it on ramps to have a look, I'm hoping it's a flexy. First question, I've read that you shouldn't purge the brakes with the ignition on because it plays merry hell with the abs system and can need a 'dealer purge'? In effect I've done this by continuing to drive it with a leak. Unfortunately I had no choice as my son's 'rentree' was the priority. Is this the case?
I've had pp2000 on it and it said 'intermittent fault front and rear RHS sensors'. I realise this could mean sensor or the wiring to it. Is there a method of checking the sensors and the plug prior to them?

Any pointers to the above gratefully received.

Just to finish, we then unloaded the BX of all my tools, put the rear seats back into position, covered the seats and boot with blankets and did the trip in the older beast. The other parents must have felt sorry for us as I parked next to all the new cars!

[ekjdm14]

I don't think there's any problem with effectively "bleeding" fluid through the system in the way that has happened, only time I've known a problem caused to an ABS pump/valve block is if air gets into the system with the ignition on (presumably the thing then tries to pump air and runs itself to death or similar?).

As long as there was still at least a bit of fluid in the reservoir when you got home I think you'll be OK just to repair the leak however caused and bleed with fresh fluid making sure not to allow air in at the master cylinder end.

As far as checking the ABS sensors, with it being an intermittent fault on both I'd suggest it's more likely to be either wiring/plug related more than the sensors. You should be able to check the resistance of the sensors with a multimeter but perhaps in your case i would probe the contacts at the ABS ECU plug and then have an assistant wiggle connectors/wiring to see if/when anything changes

[moizeau]

Cheers, there is still fluid in the reservoir, but it turns out it's not the flexy, it's the solid pipe that goes from front left to rear right. Just spoke to a chap who said he can do a repair on the pipe (replace the knackered bit with a flared piece). As I was underneath I also noticed the inner sill at the rear needs some attention. As for the info on the abs, that's what I thought, but any idea what and where to probe on the abs ecu? Never had a car with such 'gadgets'. I suppose it's time to check the BOLs wiring diagram.
Thanks again

[ekjdm14]

Oh, sorry i don't know what pins you'd have to probe at the ECU but i suppose for a start you could check the actual sensor plugs/wiring for any obvious corrosion or damage. Not sure on what the specified resistance should be for the sensors but in general anything other than open circuit and they should be working i think.

Also may be worth checking the reluctor rings for corrosion/cracks as they could possibly make the ECU think the sensor is faulty if they're sending vastly out of sync impulses through the sensor (this would usually manifest as an ABS fault where the light only came on after you'd driven a few yards though, if the light goes through the self-test routine and then stays on straight away it's an electrical issue with the sensor rather than mechanical with the reluctor rings).

I would hope the BoL reveals the pins to look for on the ABS ECU anyway though, and good to hear you've got a repair on the way. In many ways it could be a blessing in disguise it being the solid line, if it had been the flexible there's a good chance the flare nut could have stuck to the pipe and twisted it off anyway so you'd still be into re-flaring the steel line before fitting the new flexi.

[xantia_v6]

You say that the abs fault is intermittent, does the light stay on before driving, or come on after you have driven for a bit?

[moizeau]

It comes on whilst reversing off the drive, or after a minute (a few bends in the lane perhaps) or not at all. If it hasn't come on within a couple of minutes, it doesn't. If it does come on, generally, I can extinguish it by turning the ignition off then restarting the car. That presumably resets the system. It's also more common if the car has sat overnight or for a long period. It probably feels like me in the morning and needs 'warming up'.

[xantia_v6]

With those symptoms, I would be looking at the abs rings and see it they need cleaning or are corroded or split.

[moizeau]

Thanks for the tips, just off to do the brake pipes, so I'll have a look at the rings whilst it's on the ramp. Thanks

[moizeau]

The rings are fine, the rear was replaced with the bearing kit last year, the front looks good. The pipes however... are now done, with much swearing. where it screws into the rear load adjuster! 3 hours on a car lift and finally with a flame. At least the abs light didn't come on today. Wait 'til tomorrow . Control in a week, Need to keep the beast purring for another 2 years