ABS activates at low speed - no fault light on dashboard

[DaringSquirrel]

Problem with a Daewoo Lanos 2001 model with the ABS activating at low speed

Started occasionally kicking in when pulling up at a junction or in traffic - this has gradually got worse over the last few weeks which makes pulling up in traffic behind expensive cars quite interesting when a few yards from the car in front you suddenly lose the brakes!

Taken it for a couple of test drives and under heavy/emergency braking on dry roads the abs does not activate and the car pulls up quickly and straight so the brakes themselves seem fine. On the same dry road if you pull up gently (as you would at a junction) just as the car is about to stop (< 5mph) the abs activates for a few seconds which can be felt through the brake pedal.

The ABS light on the dashboard comes on when the engine is started and goes out after a few seconds as it should, when the ABS kicks in at low speeds the light does not come on again so no fault is indicated which hints that all the sensors and electronics are ok - so could this be something mechanical, like a fault with the abs pump itself? Have checked with person who drives it and it looks as though the brake fluid has not been changed for a good 40 000 miles - could dirty brake fluid have damaged the pump in some way?

Is it possible for faulty/dirty sensors to not appear as an error on the dashboard light?

Any advice would be much appreciated

[MMamdouh]

how can ABS kick in when your wheels are not on the verge of lockup??

are you sure this is an ABS issue not an out of round rotors that are causing brake pedal pulsation??

MMamdouh

[DaringSquirrel]

That's a good point, is that a common issue and if so how would I check?

Have investigated further and found that the drivers side front wheel speed sensor bracket and toothed ring and very corroded (see attached image) - the toothed ring has a crack in it but is still attached. It could be that at low speed when the break in the toothed ring passes by the sensor the hall effect is not enough to induce an AC current in the sensor and so the sensor reports that the wheel has stopped turning and so the abs is applied. Either way the service guide I got from this site (thanks to those who posted the link) says that if the toothed ring is damaged the entire CV joint needs to be replaced - which can go one of two ways.... both of which involve me bleeding and swearing lots!

Has anyone got any experience in replacing the outer CV joint on a Lanos and if so was it A) easy, B) difficult or C) harder than getting a sensible price for Daewoo parts from a UK GM dealer!

Also the bracket that holds on the speed sensor is very corroded as well and so removing the bolts without breaking them will very difficult - hoping to leave the sensor alone but am worried about damaging it when trying to remove the steering knuckle.... any further advice appreciated

[DaringSquirrel]

To see if it was the ABS I removed the fuse from the engine bay - ABS light and Brake warning light remain lit on the dash - with the ABS disabled the brakes work fine, no juddering through the peddle at low speed, so mechanically the brakes seem fine. Probably safer to drive it with the ABS disabled until I can get the CV joint replaced as if the ABS starts engaging at higher speeds it could cause an accident. Now to get it through the MOT before the end of the month.... if it fails it may force the issue