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Old 03-27-2012, 01:23 PM   #1
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Default Can I drive with Service 4WD message?

I've read through the threads about this message and know its either the switch or the encoder sensor. I can deal with that, but I'm 400 miles from home at the moment. I just need to get home. It doesn't drive any different, just got the message this morning. I don't want to grenade the drivetrain if the tcase decides to go into 4lo at 70 mph.

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Old 03-27-2012, 08:47 PM   #2
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Yeah mine comes on all the time.. Let it bump it'll be fine.
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Old 03-27-2012, 10:40 PM   #3
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Nothing wrong with driving it really. If it came on while in 4x4 then the system will remain frozen where it was last. Your mileage will probably drop and you may have excess tire wear. Other than that, I doubt you'll do any drivetrain damage. Just don't do any powerslides or donuts or anything else to bind up the system.

The most common culprit is the pushbutton control module. It is fond of dying. There is a similar TSB for your year model:

Quote:
File In Section: 04 - Driveline Axle
Bulletin No.: 02-04-21-004
Date: April, 2002
TECHNICAL
Subject: "
"Service 4WD" Indicator Illuminated, DTC B2725 Set
(Replace Transfer Case Shift Control Switch) Models:
1999-2002 Chevrolet and GMC C/K Pickup and Utility Models (Silverado, Sierra, Avalanche, Suburban, Tahoe, Yukon, Yukon XL) with Four Wheel Drive and NVG 236/246 Transfer Case (RPO NP8) Condition
Some customers may comment on the Service 4WD indicator illuminating. Upon investigation, the technician may find DTC B2725 set.
Cause
The condition may be due to a intermittent fault in the transfer case shift control switch.
Correction
Important: The transfer case shift control module should not need replacement. DO NOT replace P/N 15749703 unless diagnosis points to the module as the malfunction. Replace the transfer case shift control switch using published Service Information procedures.
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Old 03-28-2012, 07:03 AM   #4
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You most likely need an Encoder motor position sensor. Very very very very common on the 05s for some reason. Depending on how the sensor fails when the service 4wd light message comes up it may think its in 4wd low and default to that shift pattern for the transmission even though you are still in 2wd hi. If that happens you will be in 4th gear with the converter locked by 20-25 mph and going nowhere fast. This doesn't always happen but I've seen a few trucks do it.
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Old 03-30-2012, 07:31 PM   #5
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My Tahoe is occasionally giving me the dreaded "service 4WD" message. So far it always resets if I turn the truck off and restart it. How can you diagnose whether the problem is the encoder sensor or the shift control switch? Is there a code that is stored? If so, how does the average guy read the code?
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Old 03-31-2012, 03:56 PM   #6
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You can crack open the transfer case switch, the solder around where the harness attaches to the board will crack. If you can solder its an easy fix.
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Old 03-31-2012, 09:10 PM   #7
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I've done a little research and it appears the most common problem is either the encoder sensor or control switch. I found instructions how to remove the switch, but where is the encoder sensor located?
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Old 04-01-2012, 11:20 AM   #8
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I found this post regarding the control switch.

Quote:
Originally Posted by chris092183 View Post
If you have a service 4x4 light on your dash it is typically your push button 4x4 located on your dash. What happens is there are a few contacts that have cracked solder. It is very simple to fix. Just remove the buttons and look for the cracked solder and resolder it. No need for additional solder just heat up the old stuff. I forget the sequence of the fix but it's pretty easy. Better than spending 80 bucks or so.
Since the control switch is fairly easy to remove, I pulled it out, took the module apart, and sure enough, two of the solder points were cracked. I put a drop of solder onto each contact, reassembled it, and it appears to be working fine again. Might be worth checking this out if you are having the dreaded intermittent "Service 4WD" message.
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Last edited by batboy; 04-01-2012 at 11:27 AM.
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Old 04-11-2012, 10:22 PM   #9
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I had the same situation. I could turn the truck off and the message would go away. Once I drove home, I couldn't get it to do it again. As luck would have it, it just came back on 3 days ago. Once I saw it, I tried to shift into Auto4WD, 4Hi and 4Lo, none of which worked. The switch still had the LED next to 2WD lit. I shut the truck off and restarted. Then I tried all of the tcase positions. This time they worked. I thought one symptom of the switch going out is that none of the LEDs worked. However, since it's such an easy task, I'm going to pull the switch and inspect the circuit board for cracked solder joints.
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Old 04-12-2012, 06:45 AM   #10
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$60 fix on the encoder motor, simple fix. Long as LEDs are still lighting up on the control, that means the push button controller is good.
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Old 04-12-2012, 06:45 AM
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05, 4lo, 4wd, 99, drice, drive, encoder, message, on, sensor, service, shift, silverado, switch, tahoe


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