ABS brake pedal pumping

[Angle Grinder]

Just replaced a 16v i.e. with a V6 Auto that has ABS.

The brakes work fine except in the last few metres before coming to a stop.

When the car has slowed to almost a stop the brake pedal pumps 4 times and this is accompanied by a sound, which sounds a bit like something releasing pressure.

For want of a better description it sounds like the car is gently squeezing out a fart!!!

There is no evidence of pedal judder when braking at higher speeds and it only kicks in when pulling up to a stop at a junction.

Any ideas?

[Brian Hilton]

Hi Mike,
Sounds like the ABS kicking in?

Brian Hilton

[Angle Grinder]

Hi Brian,

Yes definitely a case of the ABS kicking in when it isn't required.

The question is what would cause this to be triggered?

Somehow the ABS ECU is getting the message that a wheel has locked up and this is triggering the ABS to cut in. Is this a symptom of a failing sensor or just dirt on the ABS ring generating a misleading inductance at the sensor?

I am running the car on alloys that are 14in per the original spec, but they are not OEM Lancia alloys. Could this be a factor?

Cheers
Mike

[Dian]

Mike,

I had the same problem. In my case it was broken cable, at the end, of the left rear ABS sensor. But before total brake of the cable I had the same situation as you.

You can check gap between the end of a wheel speed sensor and phonic wheel (0.55mm-0.85mm).

Next you can chek resistance of every sensor, it shoud be about 1KOhm. You may measure resistance at the electrical connection of sensors in the engine compartment for front and in the baggage compartment for rear by disconnecting the sensors from its wiring harness.

Next step, and the last is to check AC voltage reading when the wheel is spun at a speed of about one revolution per second. It shoud be about 700 MV. You may meassure AC voltage with greater speed of wheels, but the same speed for wheels of the same axle.

Dian

[Angle Grinder]

Dian,

Thanks that is excellent detailed information and it would certainly explain the symptoms.

On two occassions the ABS light has come on and whilst the light was on there was no pumping at the pedal.

I assume that the light came on because the cable to the sensor had temporarily broken, suggesting that I have the same partial loss of continuity in the wiring.

Hopefully I will be able to see the worn wires and splice them together.

Many thanks!!!

[dian]

ABS always measures readings from sensors. When you press brake pedal (accting on the switch above) it is signal for ABS central unit to start with its programm. Without pressed brake pedal and large differences between readings from sensors on the same axle you have ABS light on signaling error in ABS circuits. Then, ABS shuts itself, and the braking is the same as without ABS. So, you may disconnect one of the sensors and start you car without ABS and brake pedal pumping, but with ABS light on. I did that, disconnecting rear right sensor. I was suprised after starting the car and driving because ABS warrning lamp was off. Why? Reading from rear right was 0, and there was not differences between left and right wheel. It ment only one thing: reading from rear left was also 0. So cabling of that sensor was broken.
Unfortunately for me, I did not know that at that time. Measuring AC voltage I found bad one.
So I would start cheking first rear then front sensors, because of the greater vertical play of rear wheels and cables of the sensors.
In my case, periodical ignition of ABS warning light was after large play of the rear end of the car during driving.

Dian

[Angle Grinder]

Hi Dian,

Valuable information thanks!

Do the ABS diagnostics run everytime the pedal is pressed?

I've tried disconnecting the sensors alternately, but I have found that I need to start the car and drive it before the warning light comes on with one of the sensors disconnected. Reconnecting the sensor afterwards does not turn the light off until the engine is switched off and on again.

Do you know if the ABS diagnostics only reset after engine switch off?

I'll need to get new batteries for the voltmeter... : )

[dian]

ABS diagnostics runs all the time.
With disconnected sensor you have to drive more than 40Km/h to light ABS warning light. You are right, you must switch the engine off and on to turn the light off.
I am not sure about reseting ABS, but some post say 8 times of adding contact will reset ABS or disconnecting the battery. I think one is enough.
There is on http://www.832.dk/index_old.htm workshop manual and chapter for brakes. It is 8.32 thema but the same thing.

Dian

[iain ambrose]

I have had the same problem on my series 2 Thema for the last 3 years.
I've been looking for replacement sensors for ages now.
In the mean time I simply removed the fuse in the box covering the ABS system in the engine bay.
This means the ABS warning light is always on as the system is permanently disabled.
For the MOT I put the fuse back in as the ABS works for the brake tests etc.

[marcolino 8.32]

I have an 8.32 Tipo I (1988). The ABS warning light is always on in winter (cold) and mostly on in summer (warm): if i switch on the ignition, the warning light goes on and remains on, even if the car is not moved at all.

In summer, however, the ABS warning light goes sometimes (rarely) off _while driving_, i.e. without switching the ignition off and on. I've never had a pumping pedal, though, and all the other electrical systems work well. Recently, I've changed the ABS general protection relais, since I noticed that it was clicking when I knocked on it with my finger - it did not help.

When I came across iain ambrose's message about the fuse below the ABS system cover in the engine bay, I wanted to replace that fuse, but I cannot find such a fuse in my 8.32 ?!

any ideas?