A-TRAC and Brake Issue (1 Viewer)

[Grond]

Hey everyone, I'm new here, and just purchased my 1st 100-series last week. It's a 2000 LX470 with 250k miles, that I purchased for cheap with the goal of turning it into a DD. Everything runs and drives great, but I had the classic ABS, VSC, A-TRAC, and brake lights on, although brakes were working fine.

I tried pulling the ABS codes, but wasn't getting any communication with the ABS ECU. I took apart the ECU and debugged the circuit board per the process described in this thread:

Fix for ABS, VSC TRAC, VSC OFF, & Brake lights remain on no CEL, or how to repair an ECU

Hopefully this post saves you some money by showing you how to potentially repair your skid control ECU rather than replacing/buying a new/used one (skid control ECU part #89540-60160). These instructions do require the ability to solder surface mount components and use either an oscilloscope...

forum.ih8mud.com

Everything seemed to be okay on the board, so I reinstalled the ABS ECU, and all the lights went away. I've read that other people have had loose connectors on the ECU, so I hoped that all my problems were solved. But when I took it on a test drive in my neighborhood, the A-TRAC system kicked on whenever I accelerated ever-so-slightly. So at least the ABS "works" now, just not when I need it to.

I pulled the ABS and VSC codes by jumping Tc and E1 in the diagnostic port under the hood, and it returned 3 codes. ABS code 46, and VSC codes 43 and 47. ABS code 46 seems to correspond to the Master Cylinder Pressure Sensor, but I don't see why this would be kicking A-TRAC on when accelerating? To see if the brake pressure was the issue, I pumped the brakes with the key in and engine off. After several pumps, the buzzer went off, so I stopped. I tried rereading the codes, and now the ABS and VSC lights just flash constantly, with no pattern, when the diagnostic pins are jumped. They don't turn on when running the engine and driving normally. Hopefully this means no more codes?

With the dash lights off, and no code pattern being displayed when the diagnostic pins were jumped, I decided to test drive it again. Same A-TRAC issue as before, ABS engaging on the brakes after slight acceleration.

Does anyone have an idea on what could be causing this? I don't see how the master cylinder pressure sensor would cause A-TRAC to engage when accelerating, and I'm not getting that code anymore after pumping the brakes. I've searched the forums but haven't come across an answer. Is there a way to disable A-TRAC and ABS? The truck was braking fine hydraulically without them, and I don't need A-TRAC on my commute to work. Would like to fix the entire issue, if possible, rather than bypassing it.

Thanks in advance!

 

[KliersLC]

Others have reported uncommanded VSC/traction control when the wheel bearings were loose/worn. Have you checked to make sure everything is snug on the front end?

I believe if you pull the ABS fuse, you disable the entire system, but I'd have to take a look around and see for sure.

 

[KliersLC]

Disabling ABS on the 100 series? (2000 LX470)

All, I had two incidents, each occurring 1 week apart where the right front wheel speed sensor / ABS unit must have lost comms to whatever control unit it relays info to. I was at highway speed (60+ mph) and the traction control alarm went off on a slight incline, under normal acceleration with...

forum.ih8mud.com

Some good info in there--looks like just unplugging the sensor is the easiest way to disable it. The VSC disable thread is linked in there too.

 

[Grond]

Others have reported uncommanded VSC/traction control when the wheel bearings were loose/worn. Have you checked to make sure everything is snug on the front end?

I believe if you pull the ABS fuse, you disable the entire system, but I'd have to take a look around and see for sure.

I know the PO said he installed new wheel bearings all around. I guess I need to check those out and make sure they're all snug and installed correctly.
Do you know if having the ABS and VSC lights flashing constantly with no pattern when the diagnostic ports are jumped is a good sign that there are no codes? Or a very bad sign?
Thanks for the tips!

 

[abuck99]

Check all wheel speed sensors for continuity, cracked sensor housing or kinked/frayed/broken wire. And as suggested, check bearings for correct preload- high probability they were not serviced correctly. (Search forum for “bearing repack gurus”)

Perform a zero point calibration after you re-set your wheel bearings. (Search forum)

 

[KliersLC]

Zero point calibration please

Hi all, I need to do zero point calibration. I have done it successfully before last major overhaul but for the life of me I couldn’t find the instructions anymore. Tried searching through pieces of my FSM and this forums but I just couldn’t find it. I am looking for the reset procedure that is...

forum.ih8mud.com

Look here for the ZPC--sometimes things get lost in the clutter on the forum

 

[Grond]

Zero point calibration please

Hi all, I need to do zero point calibration. I have done it successfully before last major overhaul but for the life of me I couldn’t find the instructions anymore. Tried searching through pieces of my FSM and this forums but I just couldn’t find it. I am looking for the reset procedure that is...

forum.ih8mud.com

Look here for the ZPC--sometimes things get lost in the clutter on the forum

Thanks for the help. I will update after I troubleshoot these issues. Dumb question, but is there a difference between VSC and A-Trac? Because it's my A-Trac light that's activating when I accelerate, not my VSC Trac light.

 

[KliersLC]

Thanks for the help. I will update after I troubleshoot these issues. Dumb question, but is there a difference between VSC and A-Trac? Because it's my A-Trac light that's activating when I accelerate, not my VSC Trac light.

They are all connected. In this case, I suspect that your ABS sensors (for some reason) are showing a differential in wheel speed while the throttle is engaged. This meets the conditions for the ATRAC to apply the brakes in an attempt to get the wheel speeds to match(ish). VSC does the same thing, but it also takes input from the steering wheel, the yaw sensor and the vehicle speed sensor, and activates the brakes in a manner that will bring the vehicle back under control(hopefully). My bet is that if you drove it around at speed, your VSC would try to run you off the road.

 

[Grond]

They are all connected. In this case, I suspect that your ABS sensors (for some reason) are showing a differential in wheel speed while the throttle is engaged. This meets the conditions for the ATRAC to apply the brakes in an attempt to get the wheel speeds to match(ish). VSC does the same thing, but it also takes input from the steering wheel, the yaw sensor and the vehicle speed sensor, and activates the brakes in a manner that will bring the vehicle back under control(hopefully). My bet is that if you drove it around at speed, your VSC would try to run you off the road.

I think I (hopefully) found the culprit. Unplugged the wheel speed sensors and it drives fine, just with ABS and VSC lights on. I decided to take the wheel speed sensors off to check them, and they both pulled out surprisingly easy, without having to take the wheel off and hammer them out as some tutorials described. The front passenger sensor was completely gummed up with mud. The drivers' side was fairly clean. Is there a good way to clean the sensors and the hole they're mounted in without taking the wheel off and brake dust shield off? Looks like there's a lot of grime stuck up in there...

 

[abuck99]

To do it right you need to pull the wheel and hub/ and make sure that seal in front of the dust shield is intact- if it’s original it’s likely hard, torn and toast- letting debris and moisture in.

That seal , the one that mounts to the dust shield is spendy but important.

While you’re pulling sensors, check them against each other for continuity.