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"service 4wd System" On Info Display


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#1 MilSpec

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Posted 27 October 2008 - 08:23 AM

My moms 2003 GMC Yukon has the words Service 4wd system on the information screen I have not looked at it myself but she says the truck is still running finr no noise anything. I told her I wouldask the experts not to take it to the dealer yet hopefully its a fluild level in transfer case or a service reminder The Yukon is a SLT 2003 with appx. 60,000 miles and not XL not airride or the AWD model

Thanks

GOD BLESS OUR TROOPS

#2 5Alive

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Posted 27 October 2008 - 11:02 AM

If there is a "Service 4WD" on the message center, then that automatically means a diagnostic trouble code (DTC) has been set.

There are no transfer case DTCs that just indicate something innocent like "low on fluid," so if you're thinking you can just "top up" the transfer case and the problem will go away... think again.

The fault can be easily diagnosed with a scan tool. But not just any scan tool. Most OBD-II compliant scan tools have no trouble at all reading engine and emmissions related DTCs. It's kind of required by law... the standardization of emmission trouble code data sets. The parameter ID's for engine/emmisions faults begin with "P."

However, other chassis components that are not common to all vehicles, such as a transfer case in you mom's 4WD Yukon, are NOT required to have standardized trouble codes. The data sets can be propriatary to each manufacturer. Such is the case with GM. So, you will need to find a scan tool capable of also pulling "C" codes. One such Scantool is called a Tech II, by Vistronic. Snap-On's series of scan tools, from the 2500 model up, can also pull Chassis codes out of a GM.

The scan tool for rent at Auto Zones CANNOT pull these codes (I've tried it... reports no trouble found, even though I KNEW I had a code, and I KNEW what the code was (C0327). The popular SCANGUAGE II CANNOT pull the code. I don't think that Auto Enginuity can either, but that I'm not sure, cause I haven't tested it myself yet.

In the absence of a Scan tool, and if you still are trying to avoid a dealership visit, then you have another option. OnStar. If your mom's Onstar subscription is active, have her call OnStar from the car. OnStar will see that there is a problem, and offer to make an appointment at the nearest dealership for you. HERE IS THE CRITICAL PART: At that point, your mom should ask the operator at OnStar to READ ALOUD EVERYTHING THAT IS ON THEIR COMPUTER SCREEN RELATED TO THE FAULT THEY SEE.

As the OnStar person is reading, they will stumble through alphanumeric jibberish that means nothing to them, but means everything to you. They are in fact reading the very DTC's that you would otherwise need a scanner to read. Knowing what the possible DTC's are ahead of time helps you decipher the significance of the jibberish they might read to you.

The range of DTC's for the Transfer Case in a Yukon 4WD that might set a Service 4WD message are as follows:

C0300
C0305
C0306
C0321
C0327
C0329
C0359
C0374
C0379
C0550

B0790
B2725

U1026


When you find out what codes have been set, then you will be able to intelligently diagnose and repair the problem.

It is most likely an electrical fault, which is why the truck keeps driving normally, and you are not hearing any grinding noises, etc.

It is quite common for 2003 up vehicles to have the encoder motor sensor circuit in the transfer case shift module malfunction (CO327).

For 1999-2002 trucks, it was quite common for there to be a fault in the control switch in the dashboard.

However, I wouldn't throw either of these parts at the truck without pulling the codes first, because it could be a propshaft speed sensor or a front axle control circuit issue too. Why guess when the car is already telling you EXACTLY where to look?

Good luck!

#3 Majorleaguebass

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Posted 27 October 2008 - 02:31 PM

change out your 4wd switch, they tend to go bad...40 bucks and your done...
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#4 andrson

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Posted 27 October 2008 - 04:04 PM

My moms 2003 GMC Yukon has the words Service 4wd system on the information screen I have not looked at it myself but she says the truck is still running finr no noise anything. I told her I wouldask the experts not to take it to the dealer yet hopefully its a fluild level in transfer case or a service reminder The Yukon is a SLT 2003 with appx. 60,000 miles and not XL not airride or the AWD model

Thanks

GOD BLESS OUR TROOPS


from my experience the switch is the culprit...if you have someone scan the codes im sure its a faulty switch




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