4x4 Service Light

I have a 1999 Blazer 4x4 with the AutoTrac feature. I turn that on and when the rear wheels slip it does work properly by going into 4-HI, but it won't go out of 4-HI and I get a 'Service 4wd' light. When I push
the 2wd button I can hear a relay clicking, but it still won't go out of 4-HI. Before when this happened I could park, turn off the truck, start back up, and then shift back into 2wd, but now it won't let me. Can I read the codes myself or does it take a special scanner to pull these codes? Any ideas would be appriciated.
Thanks,
John
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I have a 1999 Blazer 4x4 with the AutoTrac feature. I turn that on and when the rear wheels slip it does work properly by going into 4-HI, but it won't go out of 4-HI and I get a 'Service 4wd' light. When I push the 2wd button I can hear a relay clicking, but it still won't go out of 4-HI. Before when this happened I could park, turn off the truck, start back up, and then shift back into 2wd, but now it won't let me. Can I read the codes myself or does it take a special scanner to pull these codes? Any ideas would be appriciated.
Thanks,
John
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Had similar problem on 99 Sierra 4X4. Replaced the control unit on the dash and problem fixed. $74 cdn at the dealer.
Jimmy
On 22 Dec 2004 13:11:51 -0800, " snipped-for-privacy@gmail.com"

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Jimmie said

I had the same symptoms and replaced the same dashboard switch module on my son's 99 Silverado.
I ordered the module from gmpartsdirect.com for $32 and put it in myself. It was easy ... and if I can do it, anyone can.
For the Silverado, the GM part number was 15709327.
Casey
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Check under the right passenger side front kick panel-- the controller is there, remove the 3 10mm nuts and unplug the module--- if the plug or terminals in the module are green or corroded, you'll have to replace the control module and plug---you can try cleaning them if they are, but it is only a temporary fix... they are known for getting water into the controller and plug, so if you do replace make sure and put some di-electric grease in the plug cavity of the new module
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snipped-for-privacy@gmail.com wrote:

You will need to have it scanned for codes. If you have the auto4hi button, you need a scan tool to extract the codes.
Ian

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I just had it scanned at AutoZone because now the 'Service 4x4' light isn't on, but the 'Service Engine Soon' light is now on. The code was 'DTC P0753; Shift Solenoid A; Circuit Electrical'. Is this the controller that everyone mentioned or something new?
Thanks, John
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