Buzz Thro Brake Pedal At Very Low Speed When Stopping

[bmthavensis]

Hi All

I've recently bought a 1998 Avensis 1.8 GLS (7AFE) saloon and have to say how impressed I am with it so far.

There is just one possible problem that is bugging me.

As I brake, immediately before the car stops (so at less than 5mph) I get a buzz/reverberation coming back through the brake pedal. It seems as if the ABS is activating momentarily. The ABS warning light on the dashboard illuminates when the ignition is switched on and then goes out as normal.

Initially I thought it may be the pads/discs but a visual inspection suggests that they are OK.

I then removed the ABS fuse from the fusebox and drove the car again. With the fuse removed the buzzing doesn't happen although the ABS light does then illuminate correctly.

I think this proves that it is something relating to the ABS system that is causing the buzz.

I then took the car to the garage I normally use and they tried 2 different diagnostic tools and neither showed any fault. To double check this I've just taken the car to another garage and again no fault was showing on the diagnostic system.

So it's fair to say I'm now totally confused.

Has anyone experienced something similar or can anyone give me a clue as to what the problem may be or how to solve it?

Thanks in advance!

[Konrad C]

Hi All

I've recently bought a 1998 Avensis 1.8 GLS (7AFE) saloon and have to say how impressed I am with it so far.

There is just one possible problem that is bugging me.

As I brake, immediately before the car stops (so at less than 5mph) I get a buzz/reverberation coming back through the brake pedal. It seems as if the ABS is activating momentarily. The ABS warning light on the dashboard illuminates when the ignition is switched on and then goes out as normal.

Initially I thought it may be the pads/discs but a visual inspection suggests that they are OK.

I then removed the ABS fuse from the fusebox and drove the car again. With the fuse removed the buzzing doesn't happen although the ABS light does then illuminate correctly.

I think this proves that it is something relating to the ABS system that is causing the buzz.

I then took the car to the garage I normally use and they tried 2 different diagnostic tools and neither showed any fault. To double check this I've just taken the car to another garage and again no fault was showing on the diagnostic system.

So it's fair to say I'm now totally confused.

Has anyone experienced something similar or can anyone give me a clue as to what the problem may be or how to solve it?

Thanks in advance!

Hi

I had the same problem last year with the same model. Brake dust causing the deep bass vibration at slow speed braking.

Initially when I cleaned the car, I hosed around the brakes to clear the dust. I was going to take the pads out and clean them and the calipers, but decided to change the disc and pads. I also bought coppperease and brake cleaner. The new brakes solve the problem - no more noise and vibration.

Start cheap and simple first, then try next solution.

One other tip is to check the wheel nuts.

Hope this helps.

[bmthavensis]

Hi All

I've recently bought a 1998 Avensis 1.8 GLS (7AFE) saloon and have to say how impressed I am with it so far.

There is just one possible problem that is bugging me.

As I brake, immediately before the car stops (so at less than 5mph) I get a buzz/reverberation coming back through the brake pedal. It seems as if the ABS is activating momentarily. The ABS warning light on the dashboard illuminates when the ignition is switched on and then goes out as normal.

Initially I thought it may be the pads/discs but a visual inspection suggests that they are OK.

I then removed the ABS fuse from the fusebox and drove the car again. With the fuse removed the buzzing doesn't happen although the ABS light does then illuminate correctly.

I think this proves that it is something relating to the ABS system that is causing the buzz.

I then took the car to the garage I normally use and they tried 2 different diagnostic tools and neither showed any fault. To double check this I've just taken the car to another garage and again no fault was showing on the diagnostic system.

So it's fair to say I'm now totally confused.

Has anyone experienced something similar or can anyone give me a clue as to what the problem may be or how to solve it?

Thanks in advance!

Hi

I had the same problem last year with the same model. Brake dust causing the deep bass vibration at slow speed braking.

Initially when I cleaned the car, I hosed around the brakes to clear the dust. I was going to take the pads out and clean them and the calipers, but decided to change the disc and pads. I also bought coppperease and brake cleaner. The new brakes solve the problem - no more noise and vibration.

Start cheap and simple first, then try next solution.

One other tip is to check the wheel nuts.

Hope this helps.

Thanks for thre reply Konrad- I had thought of changing the discs and pads but the thing that made me not do this was the fact that if I de-activated the ABS then the vibration doesn't happen. Could the dust etc only cause it to happen when the ABS is working? Could the dust etc be making some kind of "connection" to activate the sensor?

[Q.S.]

Hi All

I've recently bought a 1998 Avensis 1.8 GLS (7AFE) saloon and have to say how impressed I am with it so far.

There is just one possible problem that is bugging me.

As I brake, immediately before the car stops (so at less than 5mph) I get a buzz/reverberation coming back through the brake pedal. It seems as if the ABS is activating momentarily. The ABS warning light on the dashboard illuminates when the ignition is switched on and then goes out as normal.

Initially I thought it may be the pads/discs but a visual inspection suggests that they are OK.

I then removed the ABS fuse from the fusebox and drove the car again. With the fuse removed the buzzing doesn't happen although the ABS light does then illuminate correctly.

I think this proves that it is something relating to the ABS system that is causing the buzz.

I then took the car to the garage I normally use and they tried 2 different diagnostic tools and neither showed any fault. To double check this I've just taken the car to another garage and again no fault was showing on the diagnostic system.

So it's fair to say I'm now totally confused.

Has anyone experienced something similar or can anyone give me a clue as to what the problem may be or how to solve it?

Thanks in advance!

Hi

I had the same problem last year with the same model. Brake dust causing the deep bass vibration at slow speed braking.

Initially when I cleaned the car, I hosed around the brakes to clear the dust. I was going to take the pads out and clean them and the calipers, but decided to change the disc and pads. I also bought coppperease and brake cleaner. The new brakes solve the problem - no more noise and vibration.

Start cheap and simple first, then try next solution.

One other tip is to check the wheel nuts.

Hope this helps.

Thanks for thre reply Konrad- I had thought of changing the discs and pads but the thing that made me not do this was the fact that if I de-activated the ABS then the vibration doesn't happen. Could the dust etc only cause it to happen when the ABS is working? Could the dust etc be making some kind of "connection" to activate the sensor?

Sounds to me like a weak signal from one of the ABS wheel sensors, when the speed gets down to 5mph, it thinks the wheel has stopped turning, so activates. Check the sensor rings for dirt and debris first off, if you have no joy with that you may have to check the resistance through each individual sensor to find the faulty sensor. Because the sensor hasn't actually failed fully, it wont have registered as a fault in the ecu memory. As far as the ecu is concerned, the car just keeps locking a wheel at low speed.

[Gooli]

I had the exact same problem. I guessed that the abs sensors where clogged or faulty.

I first removed, checked and cleaned two of them, put them back, but no improvement.

Then I did the same thing to the next two, and also changed the brake fluid in the whole system.

I could not see any damage or clogging on the sensors, that should have caused the problem

on any of the sensors. But the bolts that held them in place where rusted stuck (had to drill them out).

Anyways, this cured the problem. But I to this day don´t know if it was the sensors or some problem

with the brake fluid that was causing it.

The brakes have now worked flawlessly for several years.

Earlier post on removing abs sensors : http://toyotaownersclub.com/forums/index.p...ic=89503&hl

[bmthavensis]

I had exactly the same problem. I guessed that the abs sensors where clogged or faulty.

I first removed, checked and cleaned two of them, put them back, but no improvement.

Then I did the same thing to the next two, and also changed the brake fluid in the whole system.

I could not see any damage or clogging on the sensors, that should have caused the problem

on any of the sensors. But the bolts that held them in place where rusted stuck (had to drill them out).

Anyways, this cured the problem. But I to this day don´t know if it was the sensors or some problem

with the brake fluid that was causing it.

The brakes have now worked flawlessly for several years.

Earlier post on removing abs sensors : http://toyotaownersclub.com/forums/index.p...ic=89503&hl

Guys, thank you very much for your help. I guess I have my tasks now for the next few days! I'll report back on how I got on. If, in the meantime, anyone else has any suggestions then please do give me a shout. Thanks again :)

[bmthavensis]

Time for an update and hopefully some more guidance!

Well, so far we've taken the front sensors off and cleaned them. This didn't solve the problem so we've replaced the front sensors. Again this hasn't solved the problem :(

I guess the next step is the do the same with the rear ones although this doesn't look as easy as the front ones. Does anyone know where they route to when they go up into the wheel arch? Or ideally any step by step instructions to remove them?

Finally, just so we can make sure the new sensors aren't faulty, does anyone know the resistance figures that we should be looking for when using a multimeter?

Thanks in advance again for all your help!

[bmthavensis]

Sorry to bump this one guys, but if anyone could shed some light on this before I pull out what little hair I have left, I'd really appreciate it :)

[Gooli]

Not tried changing the brake fluid? I know it is a long shot,

but its an easy thing to do. Even if it doesn't do any good, it surely doesn't do any harm either.

Often many years pass between changing it. Workshop manual says every 20 000 miles or two years.

[bmthavensis]

Weather permitting the brake fluid is the next thing to do - my problem with this is I don't quite understand how it could affect things just when the ABS is on (in other words, why wouldn't it happen when the ABS was disconnected?)

Has anyone changed the rear ABS sensors and if so could you please give me a clue as to how to do it?

Same if anyone has access to a workshop manual which details the resistance - I'd be really greatful to get that info just in case the front sensors I've put on are duds!

Thanks again

[Gooli]

You could test the resistance of all of them. Writing the measurements down on paper,

and comparing the results. Maybe gives a clue of what is wrong.

[bmthavensis]

That's probably a good idea Gooli - does anyone know how to access the rear sensors?

[Gooli]

Couldn't you just connect the instrument to the connectors connecting to the abs control unit?

These instructions are for second generation avensis. But they will probably also apply to first generation.

http://i26.tinypic.com/op9qi1.jpg

[bmthavensis]

Thanks very much Gooli!

Again that sounds a good idea. Any idea where the ABS control unit is located?

Thanks again :)

[Gooli]

Abs unit is located in the engine compartment. Not sure you can disconnect any wires though.

http://i32.tinypic.com/11abac1.jpg

Rear abs junction boxes seem to be located in front of the wheel arch, inside the car.

Should be easy following the sensor cables to locate them.

http://i31.tinypic.com/1on5on.jpg

[bmthavensis]

Gooli - thanks very much for your help! If ever I'm in Sweden or you're in the South of England I'd be happy to buy you a beer!

[Gooli]

Good to hear :) But I'll be happy if you just let us know if and how you got it sorted.

[bmthavensis]

It's not sorted yet but I'll update as soon as I know more :)

[bmthavensis]

It's not sorted yet but I'll update as soon as I know more :)

Time for an update, but it's not good news.... ABS front sensors changes, brake fluid changed but it's still buzzing. Next I guess is to check and maybe change the rear sensors - after that I'm stumped. Has anyone any other ideas please?

[Beagh1958]

To bmthavensis,

Recently had a Rover 45 into w/shop with exact same symtons. Turned out to be excitor ring around cv joint, with all rust removed, it was found that 2 sections of the ring had just rusted away over time. New cv joint cured problem. Maybe something for you to check.

Regards, Beagh.

[UCHTARAIN]

What you need is a doner car in a breakers yard. Change one thing at a time till you eliminate the problem. If you fit it and it makes no difference give the part back and move on to the next part. If you remove the fuse and the problem is gone then fit the part that the fuse connects i.e ABS unit and test. Then move on to Sensors etc etc. It may be a slightly seized caliper or rusted pads carrage/cradle, clean spotless and grease, .......but make sure your brakes are all working 100% mechanically BEFORE you start eliminating electronic controls

Regards

Fergal

[bmthavensis]

Thanks for your reply Fergal

I understand, I think, the logic of what you are saying. The bit that confuses me is that, if it is a "normal" brakes issue, then why does the noise not happen when the ABS is disconected (ie - the fuse is removed).

Unfortunately my local breakers yard don't permit the ability to try a part and take it back if it doesn't work. In fact thesedays they actually charge you to get into their yard!

[bmthavensis]

Another update...

Brakes cleaned and copper greased etc. Rear ABS sensors resistance checked.

Still no joy.

Has anyone any other ideas before I go down the ABS pump / ECU line? Can anyone recommend a reliable (inexpensive) supplier for either of those parts please?

[Gooli]

As odd as it may seem, one tire may be in a smaller diameter than the rest,

making the system think that it is slipping, as suggested here:

http://www.hondacarforum.com/honda-2/10766...bs-problem.html

Also, on some other forum a guy suggested to jack the car up, connect a volt meter to the sensors, one by one.

Setting it to AC at the lowest grade, and while slowly spinning the wheel measuring the AC voltage.

He said it should be around 2 volts. Not sure if that applies to your car, but at least both of the front sensors should

read the same voltage, as well as the rear ones.

[bmthavensis]

Thanks for the reply Gooli.

I had 4 tyres fitted when I bought the car - they are all the same make and size so hopefully that rules that potential problem out.

Over the weekend we used a multimeter and checked the resistanve to all 4 sensors and they were all in the range posted earlier in the thread, we also changed the brake fluid having cleaned the brakes first.

I'm slowly leaning to the idea its an ABS pump / ABS ECU issue - has anyone replaced these before? If so, how big a job is it please? Does anyone have any idea of potential costs?

Thanks in advance