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2004 Tahoe "service 4WD" light

Tiny
KINGDVB
  • MEMBER
  • 2004 CHEVROLET TAHOE
  • V8
  • 4WD
  • AUTOMATIC
  • 94,000 MILES
2004 chevy tahoe. 94000 miles. Driver Message center has "service 4wd" on. I can shift from 2hi, 4hi and auto 4wd OK but not into 4Low. I used a code reader to check the code. But no power to run the code reader. Found blown fuse and replaced. Code reader worked but would not pick up the 4wd code. Is the problem the front acuator, TCCM, or Switch Moter Sensor or the in-dash switch. Please help.
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Sunday, December 19th, 2010 AT 2:48 AM

4 Replies

Tiny
KHLOW2008
  • MECHANIC
  • 41,815 POSTS
You need a scan tool to retrieve the trouble codes. Most code readers do not have capabilities to read B, C or U codes.

Try a different scan tool to see if it works.
Which fuse was replaced?
Does fuse blows when shifting between 4wd.

Since you are able to use other functions of the 4WD, I believe it is not the actuator etc. More likely the 2WD low circuit has a fault.
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Sunday, December 19th, 2010 AT 4:24 AM
Tiny
KINGDVB
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  • 5 POSTS
The fuse replaced was to one of the aux/accessory fuse. The driver side cig lighter did not work and the mechanic noted that often the code reader circuit is on one of those accessory circuits. We replaced the 15 amp fuse and the code reader got power. However, it would not pick up the "service 4wd" code. The fuse replaced is still ok

When I press the 4low button, I don't hear any noise at all like when I press the other functions. Just the 4low light blinks several times.

Does the front axel actuator do anything when you switch to 4low? Or does all the activity occur in the transfer cass? And would the likely cause be in the transfer case shifter motor/sensor? Is there a way to test the shifter motor/sensor. If the shifter motor is replaced, do I have to have the TCCM module updated at a dealership?

If not the shifter then I guess all that is left is the TCCM itself in the dash?
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Sunday, December 19th, 2010 AT 2:26 PM
Tiny
KHLOW2008
  • MECHANIC
  • 41,815 POSTS
To save time and understand the problem better, get the appropriate scan tool to retrikeve trouble codes. If any are present, it would be much easier to get to the source of the problem.

Speculating is not going to help and it would cost you more in the end if you start replacing components that are good.
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Sunday, December 19th, 2010 AT 5:36 PM
Tiny
KINGDVB
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  • 5 POSTS
Will do. I will let you know what is scans
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Sunday, December 19th, 2010 AT 11:00 PM

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