ABS Problem - Light Goes Out But No ABS

[Bargain Bucket]

I have a strange ABS fault. Let me try and describe what happens.

The ABS light comes on with the ignition and goes out shortly afterwards (as it should).

The first time I slam on the brakes, the ABS appears to work normally but only very briefly. I can feel/hear the brakes being released and re-applied in rapid succession. But that stops happening after a second or so and the wheels just lock up.

Any subsequent slamming on of the brakes just results in the wheels locking up with no sign of the ABS attempting to release and re-apply the brakes. I'm fairly sure I can hear the ABS pump running during this.

Any ideas anyone?

[100SRV]

Might be worth your life to take it to a dealer? Sounds like the modulating valve block is not being driven electrically; are all the connectors mated correctly and clean?

[ELAN+2]

get some one who Knows the car/ system to ry it out. you dont say what car it is, or the conditions. Of late you would have to be giving it large on a track day or driving on a dirt track to require ABS!! check to see when the fluid was last changed, at least every two years IMHO, also, use a pressure or vacuum bleeder, not the "pump the pedal" technique!!

regards

Mark

[Bargain Bucket]

Thanks for the feedback. The car is a Lotus Carlton (ABS system the same as a standard Carlton or Senator). I've pressure bled the brakes multiple times and the pedal feel and stopping ability are fantastic !!! I've replaced the ABS ECU and ABS relays, and cleaned the connectors to the modulator - all to no avail. I'm currently testing when wet - as you say, hard to lock up in the dry (although possible - believe me). If I thought a Vauxhall dealership would have the slightest clue with what to do with a 13 year old car (older than some of their technicians by the look of it), then I'd certainly give that a go. It would annoy me though as I'm usually pretty good with any mechanical work.

I was wondering if the issue was in the fluid return system to the master cylinder. How on earth does one bleed that?

[cptsideways]

Sound like the pressure accumaultor thingybob is not fully pressurised? its like one of citroen sphere things. This is what provides the pressure. Usually when you start the car up you get a bzzzzzz at it is pumped it up, and it should repeat after a brake test or operate during. Sounds like a pressure sensor is down & not allowing it to recharge fully, as its dud its also not telling the ecu you have a pressure fault.

Just my guess

[ELAN+2]

see if a local garage can code read it for you, if the light is on there has been a fault, it needs to be "cleared" to reset the system IIRC, been a few years since I played with Carltons!! Most garages should have a Snap-On Scanner or Sykes Pickavant code reader and should be able to help. Are you near Luton?

regards

Mark

[Bargain Bucket]

This version of ABS pre-dates being able to store and read codes It's a very simple ECU. Besides, the ABS light is working as it should. Lights up when the ignition is switched on (to prove the bulb works) and goes out shortly afterwards. At no other time does the light come on.