2005 Tahoe Transfer Case - NP8 Issues

[Bob Mac]

Over the past 2 weeks, I start up Tahoe early in the morning and everything is fine so I head off to work, 20 miles. By the time I get to work I get the "Service 4WD" message. 9 hours later I start up and everything is fine so I head for home, by the time I get home I get the "Service 4WD" message. As I mentioned this has been going on for about 2 weeks now. Several days ago as I was half way home I noticed all the lights on the 4WD push button assemble were out and "Traction Control Disabled Message was on. Got up to leave the next morning and everything is back to normal. Yesterday morning I get half way to work and "Service 4WD" is on and only the red light on the 4WD push button assemble was on.

All this time I have been in 2 Wheel Drive and do not want to push any buttons for fear of getting stuck in 4Lo. I have tested the Push Button Switch Assembly and resistance is within tolerance. I have reworked the ground connections under the drivers side of the vehicle.

To me it sounds like a heat issue is causing something to fail like the Shift Motor/Encoder Assembly. Can that assembly cause all the symptoms mentioned? This weekend I plan to try to check for loose or damaged wires. I am planning on ordering a Shift Motor/Encoder Assembly to start the throwing money at the problem process, that is the most common fix that I have found in most of the threads I have read. Are there any other tests or parts I need to consider? Thanks

 

[bradyjames]

 

[George B]

If possible have someone read the TCCM codes first. I had issues with an 03 that ended up being a bad switch. It worked most of the time but was flaky. I found there were cracked solder joints on the board. I would have fixed it except when I took it apart some of the light bulbs failed so it didn't light up any more.

See this thread from a different forum.

 

[Fless]

A couple of things come to mind. Best way to start is to get the transfer case codes that are causing the Service 4wd message.

The switches can ohm correctly but I would recommend reflowing the solder joints on the switch's board and pins, or substitute a known good switch. However, getting the trouble code is paramount to point you in the right direction.

 

[rockola1971]

Not uncommon for the encoder to get worn out and flaky. Intermittent opens cause the TCMM to not know what position the shift motor is in and it throws the service 4wd message.

 

[ho69]

If you replace the shaft encoder, do you have to reprogram the transfer case control module? I have replaced the encoder and the feedback voltage from the the new shaft encoder is different from what I was getting with the original encoder.

 

[Fless]

No, the encoder motor is plug-n-play.

Are you measuring the various return voltages that indicate the drive mode? Or the 5v source voltage at the switch?