Abs Light

[Zorro]

Does anyone have any suggestions on the following:

 

ABS warning light goes out after starting engine - after about 3 seconds.

 

Warning light comes on again when travelling at about 15 mph and stays on.

 

Brakes appear to be working normally, except no ABS.

[seatkid]

Sounds like no signal from one of the 4 wheel sensors. Check the wiring to the sensors. You can see this wiring easily in the front wheel arches (there's also a connector there - check that)

[Ivor_E_Tower]

Can we elaborate?

Light usually comes on for about 3 seconds for self-check mode. ABS doesn't work below about 15mph, so once you exceed this speed the control unit is looking for certain signals, eg speed of vehicle (presumed OK as the light stays off below 15mph) and input from wheel sensors (hence suggestion that one or more is missing). Anything else the control unit may be looking for? Throttle position? Steering wheel angle?

[Zorro]

The Haynes manual says the ABS functions at speeds over 3 mph. This would suggest that it is working between 3 and 15 mph as the light stays out until 15 mph.

 

Does anyone know whether 15 mph is significant or is it just peculiar to my car?

[seatkid]

No it should activate above approx 3 mph, but there might be a time delay of two or three seconds before the ABS/Traction control faults (by which time your doing 15 mph) Try driving at 6 or 7 mph constantly to test this theory.

 

The only "inputs" are the wheel rotation sensors and brake pedal switch, ABS/TC works out speed, acceleration etc from them and looks at the % difference in speed/accelleration of the wheels to determine slip.

 

Diagnostics will show what is wrong but I would check the multiplugs and wiring near the sensors first.

[Zorro]

I thought something like that may be happening. I have tried driving for 2 or 3 minutes at 10 mph - no abs light. As soon as speedo shows 15mph the light comes on.

 

Braking and time taken to reach 15mph seems to make no difference. It all makes me wonder what the significance of 15mph is.

 

Maybe it is just a fault on my car and the abs is not activating until 15mph instead of 3mph???

 

If its the abs unit its very expensive and probably means taking it to Ford - I don't trust any of them!

[seatkid]

I don't trust any of them!

Wise man. ;)

 

Have you checked your brake lights and cruise control are working correctly (in case its a brake switch problem which are quite common).

 

Also you could try disconnecting one sensor at its multiplug and see if it makes a difference to the speed at which it faults.

 

You need to fix it for your MOT of course ;)

[Ivor_E_Tower]

May not ned to fix it for MOT - if car is not driven above 15mph!

(depends on how fast it needs to be driven on rollers for the brake test. Anyone know?)

[Mussey1]

I assume that the non function of ABS does not mean that the brakes themselves do not work.

 

If the ABS system is disconnected I would imagine that the car returns to normal brakes.

 

If this is the case then it is feasable that the car could still pass MOT as long as the brakes work. As far as I can recall MK1 LX's and many MK1 Alhambra's don't have ABS anyway.

 

Can anyone else confrm this?

 

Mussey1.

[seatkid]

ABS systems are always fail safe. Without ABS working, normal braking is maintained. But as far as I know, if a vehicle is fitted with ABS then it must be working to pass the MOT. Yes early base models didn't have ABS as standard, but the tester will see the ABS lamp.

 

taken from MOT website http://www.motcentrefinder.co.uk/nav/info_...nts.html#brakes

 

Brakes

 

Parking brake lever mechanism

Must be in good condition.

Must be fully operational.

 

Hand operated brake control valves

Service brake control

Anti-lock braking system

Mechanical brake components

Hydraulic, air and vacuum systems

Brake performance

Must be in good condition

Must be fully operational and will be tested for efficiency

[Ivor_E_Tower]

Correct, if ABS fitted it must work at time of MOT test.

What is worse:

If ABS is fitted and is not working, plod can do you for defective braking system. Not sure exactly what law/section of construction and use regs they use, but it has been done before - I remember seeing an article of a crash photographed by a red light camera, and a car which should have had ABS fitted (IIRC a Granada/scorpio) was photographed with tyre smoke from locked wheels. As it should have had ABS, plod included in the prosecution charges something about defective brakes, and the charge stuck. Be warned!

[Mussey1]

Ivor,

 

Good to know that.

However considering that in many cases ABS actually increases the braking distance due to the driver taking foot of the pedal when all the clicking starts, in some cases ABS is actually a disadvantage. In real life sometimes you hardly have time to put your foot on the brake let alone have time to 'steer round' an object.

 

I think ABS + brake assist would be a good job though!!

 

Mussey1.

[Zorro]

Thanks for all the suggestions.

 

I will try looking at the wheel sensors when the weather gets a bit warmer. Failing that I will have to find someone to sort it out for me.

 

Oh..... its just passed the MOT!

[Guest nimrod]

Try giving the sensor houseing a gentle love tap with a soft hammer! being sure not to hit the cables! if any road crap or dirt gets in the way of the sensor it cant get a correct reading of the hub and brings up a fault! this time of year with all the puddles of dirty water and road salt lying around it can build up and block the sensors vison of the hub so to speak! it may be worth your while checking to see that no crap has built up in the hub, in the castlelated section of the sensor ring causeing a false reading!

 

Or find a friendly garage that will read the fault codes! you will then have an idea of where to start looking, if it a sensor gone us! they are fairly easy to change but expect to destroy the old one getting it out! and spray a lbit of release oil around the sensor a few days in advance but minding not to get it on the disc's and pads!

[MartinWindsurf]

Just a little comment on the MOT side of things:

 

if you would be happy driving a car with the ABS having disabled itself due to a fault, then on the yr2000 Galaxy, the instrument panel is easy to pull out to access the warning LEDs - each one has an enclosed plastic cell to stop the light spreading to other warnings. The LED can be covered up easily within it's own cell so that the car can get through the MOT - it fails MOT only if there is a visible safety warning light - so my local garage told me.

 

Then your choice as to whether you persue a fix or to drive on with slightly reduced safety (maybe drive a little slower / leave greater gaps with that in mind?).

[SilverBeast]

The MOT tester should check operation of the lights for airbags and abs to check they come on with the ignition and then go out after the system self check. So if you do as suggested above it should fail its MOT.

[MartinWindsurf]

My intermittent ABS warning light appears to be fixed. I think surface rust from the drive shaft was causing the sensor to be obscured from the toothed ring - easy to see with the wheels off.  Carefully cleaned the rings and sensor faces, squirted a little wd40 into the cable connector above the wheel and all now seems ok. Heavy rain had always caused the light to come on over recent months, so water added to the rusty bits obviously combined to block the sensor. Bits of rust were also lightly jammed in the tooth ring gaps - I carefully eased them clear with a terminal screw driver. So it looks like it just needed a thorugh cleanup while being careful not to damage the fragile ring.

 

Also note that with a multimeter, test the resistance of the sensor when you have unplugged it, slowly spin the wheelhub and you should see your meter needle move up and down slightly - might need to try various resistance ranges on your meter before you see this.

 

Nb: while I agree with the chap above, I've had 3 successful/successive MOTs despite my questionable warning lamp practices - 1 was at the Ford garage who had twice previously failed to repair my airbag issue (very frustrating). I think most testers only give a quick cursory look for warning lights sometime after engine starting. There are so many lights that come on with the ignition they are not likely to spot one of them is missing. At your own risk.