Shuttle Valve replaced and...then...
Thread Starter
|
Mudding
Joined: Jan 2019
Posts: 217
Likes: 3
From: Mission, BC, Canada
Shuttle Valve replaced and...then...
I had the three Amigos - replaced the shuttle valve. Was ok for a while, then they started to appear again - usually when depressing the pedal.
I have a Autel scanner and it read there were no codes (or at least nothing that it read). I believe it can read ABS codes, so pretty sure there is nothing (then again I could be using the damn thing incorrectly).
could it really be the valve? should I try doing the bypass? are there any other tests I can do to narrow this down?
I have a Autel scanner and it read there were no codes (or at least nothing that it read). I believe it can read ABS codes, so pretty sure there is nothing (then again I could be using the damn thing incorrectly).
could it really be the valve? should I try doing the bypass? are there any other tests I can do to narrow this down?
Which Autel? I have the 619 and i can do ABS codes.. It should tell you exactly what is going on if your scanner can read ABS stuff.
Option B is something that can be done to make the system more reliable but isn't technically a "fix" -- just improves / prevents electrical issues from occurring.
Option B is something that can be done to make the system more reliable but isn't technically a "fix" -- just improves / prevents electrical issues from occurring.
Camel Trophy
Joined: Dec 2009
Posts: 3,883
Likes: 951
From: Charlotte
Hi Philip. Unfortunately, the shuttle valve switch fault code is very often, if not most often, not triggered by faulty shuttle valve switches. It's very commonly triggered by a fault in the printed circuit buried in the ABS modulator. In those cases, which based on examples reported here are the majority, replacing the shuttle valve switches does nothing to address the address the real problem.
Option B bypasses the faulty printed circuit and restores full ABS function. It's a shame that so many replace the shuttle valve switches when the switches are most likely fine, and in many if not most cases completing the Option B bypass would successfully address the real problem.
The same thing happens, although less frequently, with the wheel speed (ABS) sensors. Based on examples reported here wheel speed sensor faults are very often really problems with the electrical connectors and not the wheel speed sensors themselves.
Option B bypasses the faulty printed circuit and restores full ABS function. It's a shame that so many replace the shuttle valve switches when the switches are most likely fine, and in many if not most cases completing the Option B bypass would successfully address the real problem.
The same thing happens, although less frequently, with the wheel speed (ABS) sensors. Based on examples reported here wheel speed sensor faults are very often really problems with the electrical connectors and not the wheel speed sensors themselves.
Recovery Vehicle
Joined: Jan 2011
Posts: 1,170
Likes: 300
From: StL, MO
Hi Philip. Unfortunately, the shuttle valve switch fault code is very often, if not most often, not triggered by faulty shuttle valve switches. It's very commonly triggered by a fault in the printed circuit buried in the ABS modulator. In those cases, which based on examples reported here are the majority, replacing the shuttle valve switches does nothing to address the address the real problem.
Option B bypasses the faulty printed circuit and restores full ABS function. It's a shame that so many replace the shuttle valve switches when the switches are most likely fine, and in many if not most cases completing the Option B bypass would successfully address the real problem.
The same thing happens, although less frequently, with the wheel speed (ABS) sensors. Based on examples reported here wheel speed sensor faults are very often really problems with the electrical connectors and not the wheel speed sensors themselves.
Option B bypasses the faulty printed circuit and restores full ABS function. It's a shame that so many replace the shuttle valve switches when the switches are most likely fine, and in many if not most cases completing the Option B bypass would successfully address the real problem.
The same thing happens, although less frequently, with the wheel speed (ABS) sensors. Based on examples reported here wheel speed sensor faults are very often really problems with the electrical connectors and not the wheel speed sensors themselves.
do a search for Option B. this is a well known fault and easy fix. by doing the Option B fix you will retain full ABS, Traction Control and Hill Descent.
Recovery Vehicle
Joined: Jul 2012
Posts: 976
Likes: 154
From: Mideast US
Hi. am very interested in the comment that a failure in the printed circuit board triggers the 3 amigos. Is there any post reporting such that I can look at ?
Diagnosis of my ABS unit tells me it is doing what it should, connected oscilloscope to each wheel speed sensor (while driving) and the correct and healthy signals are being fed to the compfuser input connector.
Is the ABS control board mated to the serial number of the ECU, in such way that replacing it will not be recognized and cause more trouble if not 'christened' ?
Diagnosis of my ABS unit tells me it is doing what it should, connected oscilloscope to each wheel speed sensor (while driving) and the correct and healthy signals are being fed to the compfuser input connector.
Is the ABS control board mated to the serial number of the ECU, in such way that replacing it will not be recognized and cause more trouble if not 'christened' ?
SLABS are PNP between D2’s (but the slabs does retain some settings like non SLS or SLS Equipped for example). Option B bypasses the weak link inside the Wabco Unit that is know to fail. The normal symptom that your Wabco Unit’s internal connection is failing is when the 3 Amigo’s are triggered when you are just driving along. Then when you do a key cycle the 3 Amigo’s are gone (or the shuttle valve switch wiring is badly corroded). You can also get a similar fault when an ABS sensor is acting up, but normally upon a key cycle the ABS light will be lit until you get moving and the SLABS Unit see’s input from the wheel sensors.
A LR compatible scantool that can read LR ABS fault codes makes diagnostics a breeze.
A LR compatible scantool that can read LR ABS fault codes makes diagnostics a breeze.
Recovery Vehicle
Joined: Jul 2012
Posts: 976
Likes: 154
From: Mideast US
Thanks, Best4x4. I believe I understand now, the 'circuit board' mentioned is the tiny one inside the ABS pump; not inside the SLABS computer. My slabs pump shuttle contacts resistance readings show doing its thing properly.
The symptom is the ABS lights on from start, and after reaching about 4mph; the hill descent and the traction control join the chorus with 3 chimes, but all speed control sensors are putting good signal into the SLABS connector. Wondering if inside the SLABS there is a faulty trace/component on its board. Am sorry if appears like hijack; it is not my intention.
The symptom is the ABS lights on from start, and after reaching about 4mph; the hill descent and the traction control join the chorus with 3 chimes, but all speed control sensors are putting good signal into the SLABS connector. Wondering if inside the SLABS there is a faulty trace/component on its board. Am sorry if appears like hijack; it is not my intention.
Camel Trophy
Joined: Dec 2009
Posts: 3,883
Likes: 951
From: Charlotte
You can look at Josh Salas's original documentation showing how he came up with Option B. And as you seem to have now realized the printed circuit fault is in the modulator as I wrote, not in the SLABS.
Pro Wrench
Joined: Oct 2011
Posts: 1,709
Likes: 137
From: NE PA
My 3 amigos would always trip where we stepped on the pedal. We did option a and this continued finally sick and tired of it and noticing a small leak at the master cylinder I change the master cylinder bled out all the old brake fluid and did a full bleed the truck stops better than it ever did and haven't seen the 3 amigos since