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Hey all. I posted this in brakes because it applies to abs but it also applies here. This diagnosis and resolve comes from months of web research, testing my parts, and replacing only 2 parts, wheel bearing assemblies. My abs light only came on at 13kph but there were several symptoms which I'll list.
Symptoms: low speed abs with park brake light illumination revieled the abs fuse was removed. When fuse was installed gave these symptoms:
Aggressive abs activation causing the truck to not be able to stop at low speeds
Steering wheel at first would pull to the right. At this point I replaced the drivers side wheel bearing with sensor, the the symptom change to pulling left.
Intermittent encoder issues shifting between t case modes including locking up completely in one setting.
Button illumination in what ever setting apon startup, and sometimes remaining in 4lo for many starts. When this occurred it would not produce any acceleration. I would sit and hold 2wd sometime for 60 seconds before it would clunk into 2wd.
Awd button illumination but recieving only 2wd.
After drivers side wheel bearing was replaced I was able to drive with the abs fuse installed but gave more symptoms:
Mild low speed abs activation while coming to a stop at 13kph with no abs function under 13kph
Steering would pull to the left while low speed braking making it problematic in scenarios like parking lots and back lanes. All other braking was normal.
Here's where life got interesting, I had a service 4wd message as well and was informed by a nameless shop that the ecoder needed to be replaced. Which I believed to a point because I was having 4wd issues. I've learned alot in a short time with this issue I gotta say. Here is where my awd issues connect with my abs issues: Wheel speed is important to awd. Awd communicates with abs to know when a tire is slipping via wheel speed data. The abs sensor has 2 functions, wheel speed and slippage wheel speed. When a difference in wheel speed is determined for awd, the front drive shaft will engage and allow a small percentage of power by viscous clutch to be applied to the front drive shaft. Abs system uses the same data to determine if a wheel is slipping under braking. If it does not receive accurate wheel speed information by codes relating to wheel speed sensor circuit hi li or no communication at all by the abs wheel sensor, it can not activate the front driveshaft nor operate the abs system properly. This is why the service 4wd message can illuminate in conjunction with the abs light even intermittently. One side note here for wheel speed sensors: Wheel speed is not relevant data for 4x4 without traction control, and thus allowed me to use 4wd and not allow me to use awd. Today I'm glad to say that while the learning curve was steep it wasn't crazy expensive. More work than money this time. I could have replaced buttons, encoder, actuator, in an attempt to resolve my 4wd message. In the end it was always just the wheel bearing sensors. However if given the choice I'd replace the wheel bearing unit before replacing just a sensor. Corrosion is the true culprit and if that is true then it's safe to say moisture has entered the wheel bearing and it wont be long before the bearing starts to play anyway. Hope this helps anyone with service 4wd message.
07.24.2022
