05 Expy 4x4 High light flash

[dano]

I was 99.9% sure I posted something on this before, but cannot find it. Anyway, my 05 Expy, with 174K miles, started to have the 4x4 high light flash when I have the 4x4 set in Auto. So I checked it a little further today. The light flashes 8 times, waits 1min. 45 sec., then flashes another 8 times. I cannot tell at this point if the 4 wheel drive will engage when set in auto, as there are no slippery conditions to test it.
When I have it engaged in 4x4 high, I'm pretty sure 4 wheel drive is engaged, as the message center tells me so, and it feels like it and sounds like it engages. Didn't try low range.
Shortly after that light started flashing, the ABS and TCS lights came on.
Any thoughts?

 

[JoeD]

all of the systems you mention (Auto, ABS and TCS) reference wheel movement, sounds like you have a sensor or 2 going possibly a module

They are mag pickups and pick up debris, they get corroded, have bad connections etc.

https://www.rockauto.com/en/catalog...brake+&+wheel+hub,abs+wheel+speed+sensor,1912

 

[Habbibie]

There is a way to test if it is engaging in 4wd in auto mode on dry roads,

Come to a complete stop and put it in 2wd and bash the throttle, notice the amount of torque and power you're getting

Now repeat the test in 4auto, basing the throttle causes the back wheels to slip and that makes the PCM think you're slipping and you'll see a considerable difference in power and torque delivery and maybe even a sudden clunk or shudder on take off, that's the front diff engaging

If 2wd and 4auto yield identical results then you'll know it's not working.