Question about 1999 Chevrolet Blazer

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Where is the vacuum switch located at on the transfer case and can it be changed without pulling the transfer case? its a push button on the dash we pulled the vac hose off the accuator and there is no vacuum we bought a transfer case switch but can't seem to locate where it is on the transfer case

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  • Anonymous Mar 15, 2014

    need to know where vaccaum lines go from transfer case to accuator

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The switches are a very common problem on the S series. It screws into the top of the transfer case. The easiest way to reach it is going up next to the front drive shaft. There should be 3 vacuum lines going to it that attach in a single rubber plug onto the switch. Hope this helps.

Posted on Jan 08, 2009

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1 Answer

Push the button on the dash it shows that transfer case is engaging


Check the solenoid on the transfer case - it is vacuum actuated and you may have a problem with the vacuum line.

Feb 15, 2014 | 1995 GMC Jimmy

1 Answer

My 98 f150 was in 4WD Hi this morning when I started it. Selector switch is in 2WD position. 4WD Hi light is on, hubs (or front differential) is engaged and transfer case engage. (Feel front wheel hop...


If the switch was in the 2WD position and the transfer case was locked in a 4WD range, my 2 SWAGs would be bad switch or the connector to the shift motor is damaged / corroded or the fuse to the transfer case shift relay module is blown ( fuse # 17 ) / problem with the transfer case shift relay module.

This is without knowing if the truck was used in 4WD the night prior, and shifted out just before turning off. If this is the case, the shift motor might be stuck, and a few hits with a dead blow hammer to the transfer case might jar it free again ( do not use a metal hammer, it could damage the transfer case ).

The vacuum shift solenoids on the firewall are controlled by the GEM ( Generic Electronic Module ) which is grounding either the 2WD or 4WD solenoid, depending on the shift plate contacts in the transfer case. ( when in 4 or 4H, the contact switch plate signals the GEM, which in turn grounds the correct solenoid ).

Pulling the switch will not cause the transfer case to go back to a default position, the switch has a resistance level for each mode, and needs that value to operate the shift motor.

The resistance values for the switch between the 2 dark blue wires:
2WD - 4100 to 3700 ohms
4H - 1050 to 1150 ohms
4L - 380 to 340 ohms
- find the wire locations on the switch, mark them and remove the connector to test the resistance.

Just my opinion on the order :

1. Check the fuses for the shift motor
2. Try the old school shift method, back up ~ 50' put into park or neutral, and shift from 4WD to 2WD.
2.1. This is to see if the transfer case shift motor is bound up, and reversing might release it
3. Try hammering the transfer case with a dead blow hammer while someone shifts from 2WD to 4WD. You only need the key in the run position, if it happens quick enough after running the engine, the vacuum reservoir will still have enough vac to operate the solenoids. Don't chance running yourself over.
3.1. If this frees up the shift motor and the vacuum has bled off, you can try starting the truck and shifting into 4H then back to 2WD to get the front axle to disconnect or manually vacuum operate the front disconnect motor by applying vacuum to the pink vacuum line on the shift motor on the front axle.

Mar 05, 2011 | 1998 Ford F150 Regular Cab

1 Answer

My truck was engaged into 4 wheel drive lo and now it will not engage into anything else. It is a 2004 silverado with push button 4 wheel drive.need to know where my acuator and module is located to see if...


Your transfer case encoder motor [the thing that shifts the transfer case] is located on the LH side of the transfer case. I believe the control module should be located behind the dash near the light switch area.
If it stays in 4-Lo and the push button indicator just flashes for a while when you select, say, 2 Hi then stops blinking and goes back to the 4-Lo position then I would have someone hook up and check to see what service codes are present. I see a lot of encoder position sensors go bad but you really need a scan tool hooked up to the system to be able to watch what is happening as the shift is attempted. There aren't any vacuum controls on this system.
Hope this helps you out a bit!

Nov 28, 2010 | Chevrolet Silverado 1500 Cars & Trucks

2 Answers

I have a 1998 chevy blazer and the 4x4 well not engage. I replaced the push switch on the dash and I can hear it click on the floorboard. help please


If you hear the click in the floorboard then the problem is either the vacuum switch on the top of the transfer case, the vacuum actuator under the battery tray or the cable from the actuator to the front differential lockout. Changing all three will cost less than a hundred bucks if you shop around for the parts. The vacuum switch is the part where the three hose bundle attaches on top of the transfer case. The actuator will pull the cable when engaged, you will feel it pull when you engage the 4wd. It will move slowly. The other thing to check is the vacuum hoses between the source on the back of the motor, the hose from the switch to the actuator and the vent attached to the trans dipstick. If the vent is clogged it won't engage or disengage. Good luck

Feb 25, 2010 | 1998 Chevrolet Blazer

1 Answer

4x4 push button is not working about how much does


This is something you can do yourself if you have ever worked on a vehicle before. The part you need is called a front drive actuator valve. It costs about $ 50.00, GM part # 15165891.
Here is some more infor about it:

Main 4wd Components:
TCCM
- Transfer Case Control Module - Located behind the glove box. This is the electronic 'brains' behind the shifting.
Switch - The push button switch in the dash - driver input/indicator.
Encoder Motor - Located on the transfer case - This is what actually shifts the transfer case, and tells the TCCM what position it is in.
Vacuum Switch - Also located on the transfer case - This is what sends vacuum to the vacuum actuator (see below) when the transfer care is in 4HI or 4LO.
Vacuum Actuator - Located under the battery tray - This is what engages or disengages the front driveshaft.
Front Axle Switch - Located on the front axle - This is what tells the TCCM when the front axle is engaged.

If you want to try and replace it yourself, please let me know how it goes.

Feb 11, 2010 | 1998 GMC Jimmy

1 Answer

2003 blazer will not come out of 4 lo, auto will flash when pressed and then go out


Check the fuse to your 4wd at the fuse panel at the end of the dash drivers side. If the fuse is good, put the transmission in neutral and listen for the Transfer case encoder motor to work when you push the button on the dash for 4wd hi then to 2wd. If you do not hear it working, inspect the wire harness at the Encoder motor to make sure there not damaged in anyway due to corrosion or disconnected.
Here's some info on how the 4wd system operates on newer Blazers for all those searching for the cause of the flashing dash switch light and no engagement.

4WD System Operation on 98 up (2nd Generation) Blazers/Jimmies

The front drive shaft always turns on “shift on the fly” systems so the drive train is at the same speed in the front as the rear or the whole thing would break when engaging 4Hi or Autotrac when moving. InstaTrac (NV243 case or NP1) has 3 buttons. AutoTrac (NV246 case or NP8) has 4 buttons and clutch packs in the transfer case and is the only system for on pavement driving! Prior were the NV231 (87-93) lever and NP233 (94-97) electric motor. Your VIN # is the only sure way the dealer can get correct parts/listings!
1. Select mode on dash switch
2. Signal goes to the Transfer case control module (TCCM) or computer located in the cab on the passenger side behind the kick panel.
3. If you want 4 Lo the TCCM commands the encoder motor on the transfer case to switch a lower gear in (requires putting the shifter in Neutral and be stopped or only going 2-3mph). Note that if 4 Hi selected no action done in the transfer case. The transfer case is chain coupled and has the low and high gear. You can put all systems into Neutral by pushing the 2Hi and 4Lo button at the same time when the key is in the run position (or running but not off or acc).
4. The left front (drivers side) CV axle is always engaged to the front differential, but the right side is not coupled in 2wd. There is an actuator located under the battery tray that when commanded is vacuum actuated and pulls a cable from it to the right side CV axle coupler engaging that axle. A sensor is on that axle that tells the TCCM the axle position.
5. On 99up there is an additional vacuum switch on the firewall that switches the vacuum on and signals the TCCM also.
6. The dash light on the selector switch flashes while all this is occurring and will not switch out of 2wd unless all parts report correctly – same on the switch to any mode or back to 2wd.

So, there are a lot of possible failure areas with actuators/computer/motor/sensors/vac hoses and a special scanner is required to read the codes when the Service 4WD light comes on. But, a few things can easily be done before going to the dealer.
1. Check all vacuum hoses from the intake to the drivers side reservoir can, then to the extra switch (99up) and down to the under battery actuator. Small hose is 5/32 and larger is 7/32”.
2. See if the actuator pulls the front axle cable to engage it. If not and all hoses are good the diaphragm may be leaking on the actuator. If it engages but the light is still flashing remove the indicator switch on the front axle (only electrical plug in there) and manually push it in with the connector plugged in and see if the light stops, if so replace.
3. Listen to the encoder motor clunk when 4 Lo selected. If not working look at the wiring going to it for any cuts/breaks and repair if any found. Another indicator switch on top of this case. The fluid in the AutoTrac case should be the newer light blue Autotrak –II synthetic P/N 12378508 ($7 qt) not the red Dexron III.
4. If the light keeps flashing after this then disconnect the battery for 30 minutes for a TCCM reset, just make sure you turn off your radio first.
5. Still not working – take it to the dealer and stop at the bank on the way for $$$$!

12577412 is the part number for the Transfer Case Control Module (TCCM), or you can do the Salvage Yard for $15.00 if that's the part that has gone bad.

Jan 22, 2010 | 2003 Chevrolet Blazer

2 Answers

My 2000 blazer won,t select 4wd hi/low or auto


there is a vacuum solonoid on the firewall in the middle with 2 vac lines and a 2 wire plug
thats ur problem
push the button and smack it with the handle of a screwdriver should work

Feb 02, 2009 | 2001 Chevrolet Blazer

2 Answers

4 wheel drive on 1999 chevy blazer


99 chev blazer should have an electric motor not a vac switch...Is your controll on the dash a switch you turn.. or on the floor you shift ??

Jan 07, 2009 | 1999 Chevrolet Blazer

1 Answer

Intermittent 4wd on 98 jimmy


the module is what i would suspect. and i do believe it is in the r kick panel. i've seen the button pack on dash go bad too, but module is best bet.

Nov 14, 2008 | 1998 GMC Jimmy

4 Answers

2001 Chevy Blazer 4 wheel drive


The four wheel drive systems in these vehicles are simple. The push button controls the four wheel drive computer. The computer tells the encoder motor (on transfer case) to shift. When the transfer case shifts there is a vaccum switch on the transfer that is activated which sends vaccum to the accuator under the battery. The accuator pulls a cable to lock the front axle in. This covers all s series trucks and suv's with push button four wheel drive but not with auto or all wheel. Now to answer some questions. If your push button is lit up but will not go in to four high you should try to reset the four wheel drive computer. To reset pull the courtesy light and atc fuses for sixty seconds install fuses then cycle key on and off 5 times. If your transfer case shifts but your front end does not lock in check for vaccum at the switch on the transfer case in and out. If no vaccum out replace switch motormite number 49315 at parts store. If you have vaccum out check accuator.

Jun 02, 2008 | 2001 Chevrolet Blazer

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