ABS Problem

I posted this in the 1st gen section however I think this post is better suited for the technical chat. Being new to this forum, I hope by posting the same request in two different sections, I have not violated some rule.

I need help regarding the ABS on my Tacoma. It is a 2000 4X4 5 speed V6. Now for the problem. Initially, on about every third start-up, my ABS light would come on and remain on for the entire trip. Other times, the light would extinguish upon start-up and remain off during most of my trip (some of 5 miles, some of 100 miles). There was no identifiable pattern regarding when the light would come on during that trip or what, specifically, I was doing when the light chose to reveal itself. Many times, I was on the freeway at speed, not touching the brakes when the light would appear.

Recently, the ABS light starting coming on (and remaining on) after every start. I queried the ABS computer and discovered I had faults 32 (L/F sensor), 44 (decel sensor), and 49 (brake light switch). I pulled all four sensors, cleaned them up, and correctly re-installed them. No difference. I decided against replacing the L/F sensor at this point in time because almost everyone else with the exact same codes did so to no avail. I next pulled the ABS plug, cleaned up the male pins (including a slight tweak), applied a small amount of dielectric grease, and reinstalled the plug. The ABS light on the dash now went out after its initial 3 second “test on.”

I thought I had solved the problem. NOT. I went for a ride. As I was coming to a stop, the ABS function (vibration in the brake pedal and a ratcheting sound) occurred at about 5 MPH to stop. The first time, the ABS light stayed off, however after the second stop with the same symptoms, the light came back on (and of course, now the 5 MPH vibration was gone – ABS obviously again disabled). I went under the hood and “re-positioned” the ABS plug wires (coming out of the 90 degree ABS plug). The light again went off. Again I thought I had identified the problem (wiring at the plug) and had solved it with the re-positioning.

Now, the light will consistently go off upon start-up giving the mistaken impression all is OK. The ABS will activate from 5 MPH to stop about 60% of the time (approximately every other stop). That activation is not predictable. Sometimes, I will have 4 stops in a row that are normal, then have two or three with the vibration. The light is still off (after its 3 second “test on”) on every start-up. With the light off (and one would assume “no faults” in the system or the light would remain on), I again queried the ABS computer. I still get the three codes (32,44,49).

Now for the questions. If the computer is still throwing the 3 codes, why does the light go off? Isn't the fact the computer sees faults enough to light the ABS light? With the light off, one would think the computer believes all is well. Why is the ABS function consistently activating at under 5 MPH? Why not activate at 30 MPH? What is the computer seeing at 5 MPH that is causing it to activate? Could one of the wheel sensors be dropping out at that low speed, confusing the computer? Is this symptom something someone recognizes that they have solved? If so, what was the solution?

I cannot help but believe I have a wiring problem at the plug. The movement of the wires apparently does have an effect on the computer function. I need help.

 

Just for additional information, I decided to erase the stored codes in the ABS computer, hoping that a fresh re-boot might solve my problem. After clearing the computer, I went for a ride. My truck exhibited the same symptoms as before; no change except no fault codes returned to the computer's memory. The ABS computer believes all is well.

My only other thought regarding this issue is with the wheel sensors themselves. If one of the sensor magnets is weak (but operational), the tone wheel teeth would still easily generate the sine wave the computer is looking for during its pass through the magnetic field at higher revolutions. The AC voltage generated is directly proportional to the magnetic flux density of the magnetic field and the rotational speed of the tone wheel. When the rotational speed of that tone wheel slows, the above factors could result in a lower than expected induced voltage sent to the ABS computer. Depending on the programming of that computer, it might ignore that “reduced voltage.” If it were to read that reduced voltage as “no voltage” at one wheel, that signal would be translated into “no rotational activity.” The computer would assume that one wheel has locked up (no rotational signal) and trigger the anti-lock function.

It's possible the weak sensor would ohm-out within specs yet not have a strong enough magnetic field to satisfy the induced voltage need of the ABS computer at low rotational speeds. Has anyone solved this problem with the above symptoms? If so, what is the solution short of mindlessly throwing parts at this problem or disconnecting the ABS function altogether?

 

Noone has picked up on this question because it's HARD.
It sound like that you have a grasp of the fundamentals on how it works.
The shop manuals tend to have very specific diagnose procedures where you can look for your sensor voltage , etc and it will point out what connectors have the information.
Unfortunately Toyota has made it nearly impossible for us to post portions of their manuals any more, even so they are out of print and not available from their own dealers.
(dont' get me started)

If you want to diagnose this yourself I'd consider an account with www.alldatadiy.com and see if it isn't documented there. I was able to get the 2nd gen manual and the diagnostic procedures are in it.

 

I have been having a similar issue. Just purchased an '01 4wd double cab in February and had 32 and 44 in it. Resistance across both front wheel speed sensor were equal, measured 1k ohms each (all data says 4wd should be 1.4-1.8k and 2wd .9-1.3k ohms but since I wasn't setting a code for rf I just went with its in spec). Circuits from lf wss to abs module tested good. Attempted to swap them side to side but they have slight design differences. Tone ring looked good. Bit the bullet and replaced lf wss. Unwanted abs activation is no longer happening but abs light does still come on, sometimes immediately after start up and sometimes after a few miles. I just did this Friday and haven't looked back into it but I'm betting 44 is set. I haven't tried diaging the deceleration sensor yet. Seems simple enough you tilt it a certain way and it shows continuity on certain pins but I cant seem to find this part for purchase anywhere except Toyota which wants WAY more money than its worth. Honestly I'm just glad the unwanted abs activation is gone bc I definitely almost rear ended some people. I bought this truck bc I came across it for a fair deal and have always liked them, but after having for a few months I'm pretty underwhelmed with it.

I would go ahead and replace the faulty wss and reevaluate.

 

I also have an ABS problem. I have a '09 Tacoma 4 cylinder 4WD, the most basic one sold. I've been satisfied with it for years until a few months ago, the brakes started to decline. Now the pedal goes down too far before any brake action. A few days ago, the VSC and the ABS warning lights both came on randomly. Now they are both on all the time. The dealer says all the brakes are in good shape, and they tested the wheel speed sensors and other connections to no avail. I have a feeling that there is a problem with the master cylinder and the warning lights are just a symptom but the dealer disagrees. They spent 2 hours investigating and got nothing. I think the ABS is not working but I don't know if that is also a symptom or cause. BTW, how does one query the ABS computer? Any thoughts at all would be appreciated.

 

Are you sure that none of the tone rings on your axles are cracked? Cracked tone rings won't show up at higher speeds because the sensor does not see them as the axle is spinning too fast. The crack will show itself at low speeds and the sensor will see and think the tire is slipping and will activate abs.

 

@solarvolter do you have drum brakes in the rear? They may just need to be adjusted. Pedal travel had nothing to do with abs. It may have popped on bc the brake fluid is low so I'd check there. You check the codes by jumping terminals in the diagnostic port under the hood. I do not know which ones, I have a scan tool for this, but I'm sure there is a write up in here somewhere. I'm not familiar with toyotas but the brake combo on my taco have less than desirable performance if you ask me.

@Nfarrall I would think the crack would show regardless of speed bc it's a physical deformity. Is this a common issue? I had seen tone rings on rock auto but like I mentioned I looked and saw no real problem with it.

 

It's a fairly common issue. If you use an o scope to diagnose you will physically see the crack in the tone ring as it goes around. The truck can't see it as speed increases because the tone ring is spinning too fast to pick up hence why it is only at low speed. Pull the speed sensor and look at the tone ring with a flashlight and have someone spin the axle slowly.

 

Corvette Guy,
Rid of the ABS system altogether. Many have done this, including myself, and the brakes are so much better without it.
Do the Tundra brake mod as well.

When I removed all of the ABS crap, I installed a Wilwood proportioning valve near the MC. The OEM unit was garbage and never functioned correctly since I purchased the truck new.

Good luck.

 

Thats a terrible suggestion wtf.

 

Why is that?

 

Because one that is extra unnecessary work, two it probably won't fix his, original problem, and three costing money that again still probably won't fix the original priblem

 

Hmm, all others that have gone this route have been happy.
As for the expense, $60.00 is far cheaper for the Wilwood unit versus repairing the OEM garbage.
Price an OEM lspv, you'll get an idea and it's far cheaper than the ABS module and sensors.

Good luck OP in whichever route you take.

 

I have some what of a similar problem with my brakes. 08 v6 DCSB 4x4. Just replaced my wheel bearings about two months ago and had this occur.

My problem is that the abs will go off from 0-30mph and will pull the truck to the right. Sometimes it goes of and sometimes it doesn't. It has a mind of its own. But as soon as I go on the freeway and get above 55mph, the abs light will come on and my brakes are completely fine.

I haven't had time to pull up the codes yet, but I'll try get on that soon. I'm pretty sure my front driver abs cable might have got smashed and that maybe the cause, but I'm also wondering if it's the new wheel bearings that are causing it.

Any input is greatly appreciated!!

 

Thought I might bring this thread back seeing as how I just began experiencing the same involuntary ABS action. I have a 2005 4wd and haven't done any recent work to provoke the new tantrum. Last job done was 5 months ago rebuilding the CV axles and there was no issue after that job until now. The ABS light came on, so I took it to the car wash. This turned it off, but now I have the sketchy ABS syndrome. Next step I am going to take is, pull the sensors out, clean them thoroughly, clean the tone rings thoroughly, hope for the best. If that doesn't work I will be unplugging one sensor and cover the light with electrical tape... because that's the kind of electrician I am. Maybe sell all the sensors for more mod money! My truck does not have traction control or other gizmo's so all that is lost is the ABS function. Will post back with conclusion once concluded or colluded. No light no problem one way or the other...

 

If the abs is coming on at low speeds can coming to a stop it will either be that rust has lifted the sensor upwards, or the toner ring is causing damage. In your case on an 05 tacoma it has a magnetic ring built into them which almost never go bad, but i have seen the bearing seals go out and leak grease into the sensor portion. So easy check is to pull all the sensors and use an air gun to blast air into each sensor hole to see how much grease comes out.

 

The fix to my problem was changing the abs wire. There was a split in the wire.