I have an 05 that I just took on 1400 mile trip and 700 miles in abs light came on. Checked it with a scanner and said abs right rear no input signal. So drove home to NH and encountered snow and ice, went to use A4WD and noticed not engaging and 4x4 blinking. Then tried 4 Hi and no problems same with low. So what would be most likely culprit for not activating A4WD? All help appreciated.

Dan

 

The bad wheel speed sensor of course.

 

So the bad wheel sensor will effect the A4wd and the abs at the same time? And I just took truck out for a few miles now and the brake light in dash is on and electronic message in dash says something about electronic throttle control. Taking rear wheel off now to get rear sensor out any other ideas?

 

If the command center in the dash is indicating an issue with the electronic throttle control, then this is unrelated to the wheel sensor and you'll have to read the codes through OBD to find out what is going on with the system. Brake light should also not illuminate with a bad wheel sensor, the ABS light should. If the red brake light is on it usually indicates a dangerous situation where the brakes may fail, such as low brake fluid.

 

Any chance your e-brake is partially engaged?

 

The ABS being affected is obvious. But for the A4WD it works by sensing rear wheel spin in order to know to engage the front drive axle. With a bad sensor it is unable to detect the rear wheel spin and thus is disabled. When in 4hi or 4low there is no automatic feature so the wheel sensors are not utilized.

 

Could also be a bad wheel bearing. Excessive play in the bearing will cause a sensor fault code as well.

The bearing can be bad without making any noise, too. That's what happened to me

 

I changed passenger side rear wheel speed sensor yesterday. Didn't even go 50' down driveway and all lights in dash reset. Tried all positions and everything seems to work great. Amazing how much communication goes on between all systems. Thanks for everyone's input.

Dan

 

Just to make it clear, did this issue make the RED brake light illuminate or only the YELLOW ABS light? It was a little unclear in a couple of posts back..

In any case, I'm happy you got it solved

 

Good, glad it wasn't something more expensive with the drive system.