How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask KMP1171 Your Own Question
KMP1171, ASE Certified Technician
Category: Chevy
Satisfied Customers: 224
Experience:  Mech for 20yrs and GM Specific for 15
Type Your Chevy Question Here...
KMP1171 is online now
A new question is answered every 9 seconds

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: 6 years ago.
Category: Chevy
Expert:  KMP1171 replied 6 years ago.
I am unsure what it is you need. Are you asking about the battery drain or inop 4x4?
Customer: replied 6 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 6 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 6 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 6 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 6 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 6 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:

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;

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.

JustAnswer in the News:

Ask-a-doc Web sites: If you've got a quick question, you can try to get an answer from sites that say they have various specialists on hand to give quick answers... seen a spike since October in legal questions from readers about layoffs, unemployment and severance.
Web sites like
...leave nothing to chance.
Traffic on JustAnswer rose 14 percent...and had nearly 400,000 page views in 30 days...inquiries related to stress, high blood pressure, drinking and heart pain jumped 33 percent.
Tory Johnson, GMA Workplace Contributor, discusses work-from-home jobs, such as JustAnswer in which verified Experts answer people’s questions.
I will tell you that...the things you have to go through to be an Expert are quite rigorous.

What Customers are Saying:

  • I was having a terrible problem with the wheel bearings on my 98 Chevy Cavalier and I suspect that using this website saved me plenty of time and money. Todd L Rochester NY
< Previous | Next >
  • I was having a terrible problem with the wheel bearings on my 98 Chevy Cavalier and I suspect that using this website saved me plenty of time and money. Todd L Rochester NY
  • Wonderful service, prompt, efficient, and accurate. Couldn't have asked for more. I cannot thank you enough for your help. Mary C. Freshfield, Liverpool, UK
  • This expert is wonderful. They truly know what they are talking about, and they actually care about you. They really helped put my nerves at ease. Thank you so much!!!! Alex Los Angeles, CA
  • Thank you for all your help. It is nice to know that this service is here for people like myself, who need answers fast and are not sure who to consult. GP Hesperia, CA
  • I couldn't be more satisfied! This is the site I will always come to when I need a second opinion. Justin Kernersville, NC
  • Just let me say that this encounter has been entirely professional and most helpful. I liked that I could ask additional questions and get answered in a very short turn around. Esther Woodstock, NY
  • Thank you so much for taking your time and knowledge to support my concerns. Not only did you answer my questions, you even took it a step further with replying with more pertinent information I needed to know. Robin Elkton, Maryland

Meet The Experts:

  • GM Tech (Cam)

    GM Tech (Cam)

    Chevy Technician

    Satisfied Customers:

    GM Grand Master Technician 2007. 14 years experience.
< Last | Next >
  • GM Tech (Cam)'s Avatar

    GM Tech (Cam)

    Chevy Technician

    Satisfied Customers:

    GM Grand Master Technician 2007. 14 years experience.
  • Tim's Auto Repair's Avatar

    Tim's Auto Repair


    Satisfied Customers:

    Have owned a repair shop for 25 yrs.
  • Gary's Avatar


    Chevy Technician

    Satisfied Customers:

    15 years GM master tech
  • Dave Nova's Avatar

    Dave Nova

    Chevrolet Technician

    Satisfied Customers:

    ASE Master Certification. GM World Class Certification
  • John's Avatar


    Master A.S.E Automotive technician

    Satisfied Customers:

    A.S.E MasterTechnician A1-A8 w/L1,38 years experience General Motors Master Technician
  • Don 'Mo Lurch''s Avatar

    Don 'Mo Lurch'

    Auto Mech / Electronics

    Satisfied Customers:

    Chevrolet Cert., Heavy Line Mech, Race Shop Owner, Mobile Electronics.
  • Ron Z.'s Avatar

    Ron Z.

    - Chevy Tech -

    Satisfied Customers:

    18+yrs experience. State Inspector and Chevy Diagnostics