4WD Problems

[ejj]

Hi -

I have a 2005 Tahoe Z71 with just over 80k miles. This morning, when I fired it up, the 4WD selector indicated that the system was in neutral, and wouldn't allow me to select anything, 2H, 4H, 4L, Auto, it didn't matter. Each selection caused the button's light to blink for a few seconds, and then the neutral light re-lit.

At the same time, the check engine light came on.

This afternoon, when I left the office, the 4WD selector worked perfectly normal. I could select, and engage, any setting. Still had the CEL though.

About a month ago I got a "Service 4WD" message and the system though it was in 4L, even though it clearly wasn't. Again, about a day later, everything went back to normal, and I was able to select and engage any setting.

Any advice on the place to start to diagnose and solve this problem?

Thanks!

[tattooed4life]

I would check to see if you have any codes stored and then go from there.

[ejj]

I would check to see if you have any codes stored and then go from there.

OBDII codes, TCM codes, ?? I'm not sure which modules on the truck have retrievable codes at this point...

[tattooed4life]

obdII codes is where I would start, especially if the 4x4 service light had been on.

[ejj]

obdII codes is where I would start, especially if the 4x4 service light had been on.

I have a P0447 - EVAP DTC code, nothing transmission/4wd related.

4WD system has still been fine other than the one drive...