Service 4WD

[rich5368]

Encoder motor man. I had the same problem. Changed it and it's been all good ever since.

 

[TooTall]

Digging up the past. Did you ever find out what is exactly wrong? My wifes 07 Tahoe is showing "service 4WD" Had the dealer run the code, turns out "lost communication with the transfer case module". I checked the connector for any pins that were lose. Anybody got any ideas that I can look for this weekend. Thanks

Steven

 

[SMOKDU]

Wth??

Hey all, I just found this forum while researching this topic.

My '06 Tahoe just pulled this with me. Trying to go up my driveway (steep), it showed it was in 4HI, but I don't think it ever went in. At least I didn't hear it engage. Then when I tried to put it back in 2WD, it showed "Service 4WD", and the indicator was still in 4HI. I headed out anyway (it was in 2WD).

About 20 min later (while driving), the Stabilitrak chime sounded, showing it had been disabled. The transfer case indicator light showed it was in Neutral. It was still driving fine. After arriving at my destination, I shut it down for about an hour. When I restarted it, all was normal and it showed it was back in 2WD. The Stabilitrak was back to normal too. It hasn't done it since, but I haven't tried the 4WD yet. Any ideas?

 

[Lhustedde]

Ok it's now 2016, but for those of you who still have a 2003 Tahoe, here's a story I want to share in case you're having the same problem related to this post but have not found a solution. My "Service 4WD" light came on intermittently over the past few years but would go away by itself. I had the transfer case serviced (oil, filter, etc.) and all checked ok. 6 mos ago, it started coming on again when I started the engine, only this time the chime started binging (same sound as the Low Fuel chime) and the binging would continue for about 10 seconds. When it did this, the A/C stopped completely as did Cruise Control. Driving down the street, especially when going over a bump, the A/C and cruise control would start to work again but the Service 4WD signal stayed on. When this started happening more frequently, I took it to my mechanic who said it was likely the ignition switch. This seemed to help at first, but a week later it started happening again. I researched the topic on the internet and saw folks were switching out the 4WD selector switch. They're pretty cheap and easy to replace so I did it. No change. The next symptom that started was turning the key and NOTHING would happen. I took it back to my mechanic complaining about the "new" ignition switch not working and the same problem still happening. He finally diagnosed it. It was the wiring harness in the steering column. He proved it by showing me when the tilt steering was all the way up or all the way down, it started fine. When it was in the middle where it usually is, it wouldn't start. He found a wiring harness for it and replaced it and now everything is as it should be. If your AC stops when the Service 4WD light comes on, try keeping your tilt steering all the way up or all the way down and check the wiring harness.

 

[EzSkAnKeN]

If you are able to pull DTC's check them. If you have C0306, C0321, and C3027 it will be your TCMM. The selector switch is what fails most often first. If not then your transfer case motor (or just the encoder inside) needs replaced. If the selector lights up on start up, and then no lights show at all afterwards most likely it will be your TCMM.

 

[rndsommer]

My 01 Tahoe had the service 4wd message and the lights on the 4wd switches were out. The cause was corrosion and a loose ground on the pillar under the truck on the drivers side. Was intermittent and affected by water and bumpy roads. Cleaned ground and put in a new bolt. Fixed. Longshot but worth a look.