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msarles1, Chevy Technician
Category: Chevy
Satisfied Customers: 113
Experience:  20 Years of GM experience, Service Manager, Parts Manager, GM Master Tech, ASE Master Tech
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2003 Chevy Blazer: 4-wheel drive that has never worked..snowstorm

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I have a 2-door, 5sp 2003 Chevy Blazer with 4-wheel drive that has never worked right. It has broken every year since I got it and it doesn't ever seem to get fixed. When I was leasing it I would bring it to the dealer and they would get it working again only to have it go at the first snowstorm. When I bought it from the lease (in every other respect the truck is perfect) they suddenly told me the problem could be a $586 actuator that might be causing this. Has anyone had a similar experience and can anyone tell me that if I shell out the $586 this will fix it? I love my truck, but I live in the NE and it's rather useless in the winter without the 4wd. Thanks!
they have had a lot of problems with the vacuum switches on the transfer case itself, i will give something from gm, read this it will help.please click on the diagrams thanks Service Information Home Publications Number Search New Bulletins Bulletin Search Feedback Help
2003 Chevrolet Blazer - 4WD | Blazer, S10 Pickup, Jimmy, Sonoma (VIN S/T) Service Manual | HVAC | Bulletins By Category | Technical | Document ID:(NNN) NNN-NNNN
#03-01-38-009: HVAC Mode Switch Inoperative or Stuck in Vent Mode, Oil in HVAC Control Head and/or Vacuum Lines (Replace Transfer Case Vacuum Switch and Contaminated HVAC Components) - (Jun 25, 2003)

Subject:HVAC Mode Switch Inoperative or Stuck in Vent Mode, Oil in HVAC Control Head and/or Vacuum Lines (Replace Transfer Case Vacuum Switch and Contaminated HVAC Components)

Models:2001-2003 Chevrolet Blazer, S10
2001-2003 GMC Sonoma
2001 GMC Envoy, Jimmy
2001-2003 GMC Jimmy (Export Canada Only)
with 4WD and Two-Speed Electric Shift Transfer Case (RPO NP1)



Some customers may comment that the HVAC mode switch may be inoperative or stuck in the vent mode. After some diagnosis, oil in the HVAC control head and/or vacuum lines may be found.


When the transmission or transfer case heat up, the oil may expand and find its way into the transfer case vacuum switch. This oil expulsion may cause the vacuum switch seal to fail and allow transfer case oil to be drawn into the HVAC vacuum lines.


Replace the transfer case vacuum switch. Refer to the Transfer Case Vacuum Switch Replacement procedure in the Transfer Case sub-section of the Service Manual. Also, replace all contaminated parts in the HVAC system.

Parts Information

Part Number



Switch -Transfer Case Vacuum

Parts are currently available from GMSPO.

Warranty Information

For vehicles repaired under warranty, use:

Labor Operation


Labor Time


Switch, Vacuum Control Transfer Case - Replace

0.6 hr


Diagnosis Time

0-0.3 hr


With Skid Plate

0.2 hr

Any additional time for replacement of HVAC components must be submitted as Other Labor Hours and requires appropriate authorization.

GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.


© 2008 General Motors Corporation. All rights reserved. this is also a heating issue fix. this switch cause's 2 problems, also check for proper vacum at the switch
Customer: replied 8 years ago.
Thanks for getting back to me; I cannot view any of the information you sent over; it's telling me that I'm not authorized to view the information.

So basically, how much do you think it would be to fix this? They're telling me the whole case needs to be replaced ($586 for the part). this sounds like it could be it, as they are always able to get it reset and it works when they're testing it, but then when I go to use it, it doesn't work. Once I did hear it grind and smelled something electrical, but that was the only time that happened. Every other time it sounds like it's trying to engage and then just doesn't. It has even been stuck in 4wd at times and won't go back to 2.

Thanks again!
have some replace the vacum switch on the transfer case first, about a 20 dollar part. that is where i would start. the part number is XXXXX the text i sent you. try it you will be amazed at the results
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