ABS issues on a 2002 Corolla

[NTT]

Let me begin.

The issue is the following, when coming to a stop, right near the end when braking, the ABS unit engages. When hard braking to full stop, it doesnt happen. Only at very low speeds. No ABS light is/comes on during all this. Now I found several topics, discussing similar issues. I did/checked the following:

• Took out both the front sensors, cleaned them, checked the seating area and the ABS rings on wear. Noticed the bolt on the front right sensor had broken off and kit was used to secure it...
• Replaced the front right knuckle, bearing, sensor and ABS ring, since we couldn't drill out the broken off bolt. Issue remained
• Dropped the car off at friendly mechanic to check and he says he measured all the ABS sensors and those seemed to check out.
• When unplugging a sensor, the ABS light comes on as well, so the wiring from the sensor to the module seems fine. He noted that it could be the ABS module itself.
• I ordered a second hand from a parts dealer, we replaced the module for one with an exact match with the older one. After a lot of hassle bleeding the system, issue remains.

Now, there is a chance, however small, that the 2nd ABS module also has a fault in it, but to me, it seems weird that it is the EXACT same issue. The cost for a new front left sensor and ring isn't that much, so I will be replacing those too. But could it be a rear sensor? They are integrated inside the hub so dirt couldn't be an issue right?

Since it is becoming a costly issue, I ask you, do you have any experience with this kind of issue?

Any idea's, or suggestions at this point will be greatly appreciated

[flash22]

you need to read the live data for each wheel sensor i highly suspect that you have a crack in the magnet in one of the rear bearings (the Hub and bearing are 1 unit and it's not worth messing about with bearings) if it is the issue use a decent quality item like SKF or Blueprint

[oldcodger]

@flash22 has a possible answer there, but you will need a good /expensive  OBD reader to give you such data, not cheap, though would assume a decent garage would have one ?

You can measure the static resistance of all the sensor using a simple multimeter.

We had a very similar problem , just pulling up, the last meter or so, and it felt like the ABS came on ??  Also happened readily when reversing slowly up the driveway.

Checked the sensors as above all ok, removed the front ones to see if their faces were ok, but the bolts badly corroded, had to drill one out and retap.

Again all looked ok and the abs ring teeth looked clean.

However, the abs ring fit onto the cone shaped cover of the CV joint and if like our your will find it may be rather rusty.

On ours, the rust got under the ring and suspect the pressure split the ring, which although seemingly working ok, somehow slips at that very low speed ??

It can be difficult to spot the split in situ but after we applied some brake cleaner to the ring it became looser to the touch, so showing us the problem.

You can buy the rings on their own .

 

 

 

[NTT]

Thanks for the advise @flash22 and @oldcodger. I will look into contacting a garage who might do it for a reasonable price and see if we can figure out which sensor might be busted. Will report back on this!

[NTT]

Unfortunately, after changing both rear wheel bearings, the problem still persists @flash22. Would disconnecting 1 sensor, then drive the car, help with diagnosing which wire might be kaputt?

A friend of mine came with another possible cause, when your brake discs are warped (not saying mine are) that could cause the ABS sensor to go off as well?

[flash22]

the only way is to use live data and find what sensor is dropping out - when you changed out the ABS module did you perform a calibration?

[Mjolinor]

This is not Toyota specific. I am not an expert on Toyota.

I have seen this situation in the past on various cars where the brake light switch is not a simple switch but has two switches in. One is normally open and one is normally closed. The computer expects that these two switches change state with very specific timing and if that timing errors the ABS does stupid things.

Firm pressure will work fine but light pressure or slow application triggers the fault.

It can be caused by damp in the switch or a worn / faulty switch.

Do Toyota have a duel brake switch or a simple single pole?

 

[NTT]

6 hours ago, flash22 said:

the only way is to use live data and find what sensor is dropping out - when you changed out the ABS module did you perform a calibration?

I myself did not change that, a buddy if mine did that. So I will need to check on that. Any idea on such a thing should be done? Do you need specific equipment for that?

 

[oldcodger]

Worth checking that switch as @Mjolinor mentions  as the electrical diagrams seem to show the switch feeding the stop lights and ABS unit, but no details if its a single or dual switch unit, eg 2 wire or 4 ?

To monitor the Live Data for the ABS sensors you need a suitable OBD2 reader, though only the more expensive ones have those features, most garages or very keen diyers  should have one.

You can see how it works on ytube etc - but does not always mean it will be the cause of your problem.

Quiet a bit of ABS calibration  info on ytube.

Just re-reading your posts and of all the parts you have replaced, but no mention of the relatively cheap front 2 sensors ? vs the expense of the rears/hub ?

The front ABS sensor are connected to the wiring loom just under the top of the wheel arch so could be a poor connection/ corrosion on them as if the wheel arch lines has been damaged/ loose water could esily get in.

 

 

[NTT]

Hi @oldcodger,

Thanks for your reply. So far I have changed the front sensor, front bearing and knuckle (since the sensor bolt was torn off) and both rear bearings/hubs. I haven't been working on the car lately due to study stuff, but I still tend to find out what is wrong with the car. I am looking into getting into it a proper shop and see if they can figure out what is happening since I have been spending to much money already 😅

By the way, do you happen to know why the brake pedal VERY firm before starting the car? When you start the car, it drops and operates normally. Never had that on a car before..

[oldcodger]

Hi,

The brake pedal being very firm before starting the car or just after switching the engine off, will likely be because there is no vacuum from the engine , so no pressure on the brake Servo which gives you the assistance / lighter feel on the brake pedal, Brake Servos standard on most modern cars.

Assume its just your typing, but you say above you have replaced the front Sensor ( singular) , do you really mean you have repaced both front sensors ?

Cannot offer any more help on your ABS problem but worth getting the problem diagnosed before spending on parts that 'might' be the cause.

As originally said  your problem  sounded  so much like the one we had which turned out to be the slipping ABS reluctor ring.

What we would do as a simple final check before doing anything else expensive, if you look under the front of the car, you can just see a small section of reluctor ring just under the hub,  suggest you  put a mark the ring and the hub  then  run the car /brakes to induce the abs problem a few times, then check those marks and see if they are still in position or has the ring moved ?

The ring is can be seen from underneath  as in this photo from  another make,  just that on the Corolla is a litte less exposed, but still viewable.