Another Service 4wd Issue

bfr57 · January 5, 2010

Have searched for my particular issue and haven't seen this one: Have the Service 4WD message lit, sometime intermittent, but becoming more frequent. The light on 4WD panel is lit in 2WD, but I can't shift into 4WD at all. No noises of motor or lights flashing, etc. It has never shifted itself into 4WD when starting or out when in. I live in AZ, so moisture is not an issue. It sounds like a sensor, but?? Anybody else had this particular issue?

2005LT · January 5, 2010

There are a number of guys on here who can probably point you in the right direction but will require some more detail about your truck. My impression is that you have a GMT-800 (1999-2006)?

bfr57 · January 6, 2010

Sorry, guess that would help. I have a 05 Avalanche, 5.3L with flex fuel option, auto, 63K miles.

rdtahoe00 · January 6, 2010

Have searched for my particular issue and haven't seen this one: Have the Service 4WD message lit, sometime intermittent, but becoming more frequent. The light on 4WD panel is lit in 2WD, but I can't shift into 4WD at all. No noises of motor or lights flashing, etc. It has never shifted itself into 4WD when starting or out when in. I live in AZ, so moisture is not an issue. It sounds like a sensor, but?? Anybody else had this particular issue?

mine did the same thing, it was the switch - $70 dealer part. Easy to pull out once the bezel is off. if you have a buddy with the same switch, see if you can change it out to check it. known issue with these switches going bad.

bigredmariner · January 6, 2010

Could be the switch but by 05 and 06 they pretty much had the switch thing fixed. If it turns out to not be the switch the encoder motor sensor would be the next thing to check/replace. You can pm me for more detail if needed.

brockermatt · January 6, 2010

I live in AZ as well and I have had this happen every now and then. As strange as it sounds it usually starts happening right before I lose my battery or as my battery is starting to go bad.

dwhults · January 6, 2010

Have the codes read before dumping money into it. Go to Advanced Auto, AutoZone, etc. They will be able to read the code of the TCCM. I know my Actron CP9190 reads TCCM and TCM codes from GMT-800s.

bfr57 · January 6, 2010

That was going to be my next question: What is a good scanner that'll do chassis codes? I see the Actron is a little pricey. Is there any others out there that'll do both powertrain and chassis codes decently priced? I've been wanting to get one, so I might as well take the money I would pay a shop to plug in and put it towards another tool!

wtbrowne · January 6, 2010

I took mine in today for the same problem. The dealer ordered a new 4WD switch and says they'll have it tomorrow.

dwhults · January 6, 2010

I have the Actron CP9190 which does everything from '86-Present. The CP9180 is the same but only '96 and up. check eBay. You can get one for around $145. One of the best investments I made. Unfortunately it doesnt read TCCM and Tranny codes on my GMT-400 but it did on my friends GMT-800.

Maybe the CP9185 will do the TCCM, not 100% on the CP9180.