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        General >> Problems >> ABS Engages on Dry road @ low speed
        
(Message started by: Sutton09 on Apr 16^th, 2005, 3:27pm)

Title: ABS Engages on Dry road @ low speed
Post by Sutton09 on Apr 16^th, 2005, 3:27pm

Hi there folks

Noticed a disturbing problem on my way home from work.

When i was driving home from work this morning i notice that the abs is activating under normal breaking at relatively low speeds, the brake pedal also feels excessivly spongy, checked fluid levels, all OK, no sign of leaks anywhere in the braking system. only thing that may contribute is that my n/s front wheel bearing needs replaced and as such had been giving me a wobble recently, now the wobble is still there but the pedal does feel like it has more travel, after i noticed this i tested the brakes out and when heavy pressure was applied the brakes operated as they should, it just seems to be under normal braking, and only in the "final" part of braking ie the point where i apply most pressure to the pedal. any tips would be greatly appreciated,

i was just thinking of pulling the abs fuse in the meantime

Title: Re: ABS Engages on Dry road @ low speed
Post by scorpio_man on Apr 16^th, 2005, 4:26pm

hi there

you need to fix the wheel bearing, pronto! :o the abs error is telling the wheel/hub is moving about. not good. also check tyre pressures. it has been known to affect the abs, but in your case, i doubt it.

Title: Re: ABS Engages on Dry road @ low speed
Post by Sutton09 on Apr 16^th, 2005, 4:39pm

Booked in for monday morning :)

Thanks for that,

Title: Re: ABS Engages on Dry road @ low speed
Post by nodge on Apr 16^th, 2005, 6:30pm

I have the same problem so I'd be interested to know how you get on. Mine is not connected to the wheel bearing though. Obviously if you know your wheel bearing is failing then you need to get it replaced. My abs activates just as I come to a stop, say from 5 mph to a standstill. It was explained to me that one of the abs sensors is getting a weak signal for some reason and at say 5mph the signal is so weak it thinks the wheel has actually stopped turning and so the abs activates. I don't work on the car myself but the mechanic who does said the sensors were seized in place and he didn't want to force them for fear of braking them. The problem is I don't know which wheel the problem is on. I've been living with it for ages now but I would like to get it sorted. Does anyone know if an obd check would show anything?

Nodge

Title: Re: ABS Engages on Dry road @ low speed
Post by ren on Apr 16^th, 2005, 8:46pm

Hi Nodge
on my previous car a 2.0ltr scorp
i had a similar problem i took into
a garage a one man operation and
he had a machine that he plugged into
the car and it identified that the rear right
abs sensor was faulty,which i changed
it wasnt a laptop connection as i believe
obd leads connect thro tho.
Ren

Title: Re: ABS Engages on Dry road @ low speed
Post by Eddie on Apr 17^th, 2005, 4:21am

ABS triggering at very low speed,i.e. just as the car is stopping is usually a faulty sensor.
One way to check a sensor is to jack up each corner at a time and disconnect the sensor at the plug a coupple of feet up the cable,connect a meter on low voltage range and have someone spin the wheel,you should get a low voltage reading. They can also be checked by measuring the resistance acroos the two pins of the connector,I cant remeber the figure you would be looking for. Do all four and the odd one out is the culprit.

Changing the sensor on some cars is usually a destructive proccess,the old one having to be broken up and dug out. It is just a coil in a can with a magnet.

eddie

Title: Re: ABS Engages on Dry road @ low speed
Post by nodge on Apr 17^th, 2005, 4:30pm

Thanks Ren & Eddie. Not sure what Ren's mechanic did but failing any more info I'll give Eddie's method a go. I'll add it to my "To Do" list.

Nodge

Title: Re: ABS Engages on Dry road @ low speed
Post by ren on Apr 17^th, 2005, 4:56pm

Hi Nodge
Iwas trying to answer your question if a obd check would
show the sensor at fault,
The lead was connected to the connector in the coin box
were the obd lead connects to,but it wasnt a laptop that
was connected to the lead,it was an handheld machine
with a display which read o/s/r sens FLT,
so i would have thought a obd check would tell which
sensor at fault
Ren

Title: Re: ABS Engages on Dry road @ low speed
Post by SaveTheNight on Apr 17^th, 2005, 6:41pm

hiya .. that machine is called a breakout box ..its just a larger and clearer way of checking the ECU pins .. you can check them in exactly the same way right at the ECU between each sensor terminal.. but Eddie's way is simpler ..in fact there is no need to spin the wheel even as the resistance itself across the sensor wires will tell you which is faulty .. the sensation you feel is caused by the sensor NOT cutting out below five mile an hour as it should do .. usually due to an incorrect air gap at the sensor.. ie: muck on the sensor reducing the gap or as everyone says ..a faulty sensor .. the feeling is as you say quite disconcerting when it happens .... regards ....... STN

Title: Re: ABS Engages on Dry road @ low speed
Post by Sutton09 on Apr 17^th, 2005, 10:20pm

Hi again.. i've been busy today

Wheel bearing replaced, new discs and pads all round. same problem. but it doesn't always happen @ < 5mph. although it is intermittant. usually when i get the problem the brake pedal has far more traval than normal. and when pressed can get right to the floor, it then firms up again. system has bled twice, no leaks. any ideas

I am now thinking it may be a combination of ABS sensor as suggested and perhaps a servo issue

any help would be appreciated

Title: Re: ABS Engages on Dry road @ low speed
Post by nodge on Apr 17^th, 2005, 11:51pm

Hi,
If the pedal's hitting the floor I'd be suspecting the master cylinder. No idea why the abs is activating though - I think it might be a symptom rather than the cause. I'm not a mechanic so hopefully someone who knows more than me will give you an answer.
Nodge

Title: Re: ABS Engages on Dry road @ low speed
Post by Sutton09 on Apr 18^th, 2005, 12:15am

The thing is braking is fine on a firm "plant" of the pedal, its just normal braking that gives the symptoms. emergency stops are good.. ie abs kicking in as needed and with the fuse out wheels locking

Title: Re: ABS Engages on Dry road @ low speed
Post by SaveTheNight on Apr 18^th, 2005, 12:39am

Hi again sutton .. i would still think that the effect you are experiencing is the sensor fault ..as I say it is quite disconcerting when it does it and its pretty common too ..the abs HAS to cut out below five miles per hour to avoid the wheel sensors bringing in ABS when parking or just about to halt when the sensor will think that the wheel has stopped and therfore activate ABS ..it's THIS that is not working correctly that is bring your ABS on ..although intermittent I suspect that it NEVER happens at above five or eight mph ? .. the long pedal travel can still be explained by the ABS taking fluid at that time .. check the sensors especially the fronts at the first connector by the strut and clean and white grease them .. ohms test them if you have the facility ..and clean them if poss ..if you dont want to risk removing them then remove the inner dust cap from the stub axle where you can then clean the sensor with a rag on a thin screwdriver ... hth ..... STN

Title: Re: ABS Engages on Dry road @ low speed
Post by Sutton09 on Apr 18^th, 2005, 12:51am

Thanks very much STN, will try and clean sensors tomorrow and let you know how i get on

Guys like you are what makes owning a scrop what it is

Title: Re: ABS Engages on Dry road @ low speed
Post by nodge on Apr 26^th, 2005, 9:17am

Hi Sutton,

Just be interested to know if you've found the cause of the problem yet.

Nodge

Title: Re: ABS Engages on Dry road @ low speed
Post by Sutton09 on Apr 29^th, 2005, 11:57pm

Hi Nodge

Ok, Turned out to be the wheel bearing, although it had been replaced, turned out the Hub itself had sustained some damage, replaced the strut as a whole, and now i have no problems at all, stops on a dime. Garage said that he found it strange as the hub seemed OK when the bearing was changed, but 500 miles later it was whining again, this was then attributed to the hub or flange as he said (i'm not a mechanic). anyway bought a whole new strut as he also found the shocker needed done, after that was done she is great. i guess the play in the wheel was causing choas with the ABS

Thanks for all your help guys

Title: Re: ABS Engages on Dry road @ low speed
Post by SaveTheNight on Apr 30^th, 2005, 2:06am

glad to know you sorted it sutton09 .. can i ask whether you changed the sensor ? ..or did one come fitted to the s/h hub/strut ? .. < in which case you automatically " changed " the sensor too > .... regards .... STN

Title: Re: ABS Engages on Dry road @ low speed
Post by Sutton09 on Apr 30^th, 2005, 10:21pm

Came with the strut as far as i know

Title: Re: ABS Engages on Dry road @ low speed
Post by SaveTheNight on May 1^st, 2005, 9:54am

cheers sutton ... STN