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KMP1171
KMP1171, ASE Certified Technician
Category: Chevy
Satisfied Customers: 224
Experience:  Mech for 20yrs and GM Specific for 15
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I have a 99 Blazer LT with RPO NP8 (Auto 4wd). A couple of

Customer Question

I have a 99 Blazer LT with RPO NP8 (Auto 4wd). A couple of months ago the Service 4WD light came on. At the same time the battery died. I replaced the battery and the new battery kept dying as well. I put the car up on lifts after it was sitting for a couple hours and the transfer case was warm. We hooked up the diagnostics and got a code for the encoder motor. I figured there is a short somewhere in the motor.

The old motor is working properly with the Service 4WD light on. Sometimes when the battery goes completely dead the light disappears for a couple of days before coming back on.

Online I ordered:

"DORMAN TRANSFER CASE MOTOR -- Connector has a square plug with 4 pins and a rectangular plug with 6 pins; This is a high quality, direct-fit transfer case motor that replaces OE part number 12474401.
Fits: No Core, Fits New Venture Gear 136/236/246 Transfer Case, with RPO Code NP8, Square Plug with 4 Pins & Rectangular Plug with 6 Pins."

There were pretty detailed instructions on how to get the transfer case in neutral and in the proper position to replace the motor. I followed the instructions installing but could not get the Blazer out of transfer case neutral. I put the part back in and it began working again. I guessed I got a defective part so I called the supplier and they exchanged it. The same thing happened again. I think it is strange that I would have gotten two defective parts.

I am trying again with a different supplier. Is there a step I am missing?
Submitted: 4 years ago.
Category: Chevy
Expert:  KMP1171 replied 4 years ago.
I am unsure what it is you need. Are you asking about the battery drain or inop 4x4?
Customer: replied 4 years ago.
I am sorry I wasa not clear. I am trying to figure out how to replace the encoder motor. I have tried twice now using the DORMAN replacement for part number 12474401 without success. I cannot get the vehicle to shift out of transfer case neutral after I install the new part.

However, when I put the original encoder motor back in, the transfer case works as expected. I can get it out of neutral and the vehicle shifts into and out of 4wd with the Auto 4wd feature working.

I am trying to find out if there is some step I could possibly be missing that is required when a new encoder motor is installed. I can get the old one back in and it works. I follow the same steps each time, so mechanically I think am doing it correctly.

Is there a step you know of that needs to be performed with a new encoder motor that I could be missing?
Expert:  KMP1171 replied 4 years ago.
As far as programming or anything like that no. But assuming that the motor you bought is good. Make sure that the position of the new one matches the position of the old one and that that is the position of the key on t-case
Customer: replied 4 years ago.
can you please let me know specifically what "the position of the key on t-case" means? the old motor comes out in neutral and the new one come with a plastic piece that holds it in neutral. once i get the new motor in postion i remove the plastic piece and bolt it in place.

i think i am getting the transfer case properly in neutral before starting. is is correct that i could not get the old motor out if the t-case wsa not in neutral?
Expert:  KMP1171 replied 4 years ago.
Try this whith the new one not installed on t-case hook up connector and try to switch. do same with old let me know
Customer: replied 4 years ago.
I just got the new part today. With the holiday weekend I probalby will not get to work on this until next week. The blazer shifting into and out of 4wd now with the old unit. I will get the new one in per the instructions. Each time I have had no problem getting the t-case into neutral and lining up the new motor. If I have a problem I will let you know. Either way I will glady award the $15 for your efforts. I am just frustrated at this point as to why I can't replace the part.
Customer: replied 4 years ago.
I don't know if this helps. I have the rpo code np8. I am pretty sure the part I am trying to replace in GM 12474401. I have seen replacements for this part online at many sites.

The site I ordered the new part from:

http://www.monsterautoparts.com/CHEVROLET/s10/s10_%20blazer/chevrolet_s10_blazer_transfer_ca.htm

I ordered the first one on the web page which indicates it works with NP8 Auto 4WD

I have also seen the same part 12474401 on sites like this one;

http://www.am-autoparts.com/AM/Four-Wheel-Drive-Components/Chevrolet/S10Blazer/-/AM-37536369/?utm_medium=shoppingengine&utm_source=ShopzillaSF

It says it replaces 12474401 but that it does not work with 4 button dash control w/ Auto 4WD.

This is confusing to me as both units claim to replace the same part number but one works with Auto 4WD and on does not. I just wondering if I keep getting parts that are not meant to work with Auto 4WD.

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KMP1171
KMP1171
Chevy Mechanic
224 Satisfied Customers
Mech for 20yrs and GM Specific for 15