ABS Issue

I'm new to the forum so I apologize for the long post.

I need help regarding the ABS on my Tacoma. It is a 2000 4X4 5 speed V6 TRD. 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/R 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.

 

Don't think anyone has solved this issue. I recommend disconnecting the abs all together.

 

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?

 

Plausible theory. Not sure if it would be cheaper to test your old sensors or just buy new ones. These systems are very sensitive so there are tons of things that can cause the reading from the sensor to be out of spec at the ecm.

 

This may be a stupid suggestion, but have you checked your brake fluid?

 

THE SOLUTION to ABS CAPDE 49: I’m posting this here because I know that many of you must be experiencing the problem. After a year of troubleshooting and a couple of unnecessary parts replaced; I found that the 1157 LED bulbs I used for replacement of my tail lights was the cause of the ABS fault (code 49). After some research on forums (someone suggested: “ have you made any changes or upgrades to the brake lights”
Today I replaced the LEDs back to incandescent and the problem is solved.

PM me if you need more info.