Another blazer 4x4 problem

[chevyman69]

I have a 2000 blazer 4.3, 3 button 4x4 switch with np1 case. When i try to shift it into 4hi the light blinks and i hear a clicking from the box in the kick panel on pass. side, i dont hear anything from the t-case motor and then the the 4hi light stops blinking and just stays in 2wd. i checked all lines and the part under the batt. tray all looks good. replaced the t-case switch and put on a new t-case motor. still getting the same thing. before i did any of the other stuff i did find a blowen fuse for the tranny under the hood and replaced it. now when i had the t-case motor off i tryed to turn the shaft on the t-case that goes into the tcase motor and couldnt get it to move at all, is that normal? maybe the box in the kick panel is bad, hell i dont know. no dash lights on either. thanks for any help you can offer.

[travis2822]

I had a similar problem with my 99 3 button. You may want to do a search on the forum to get some info. My solution was a simple one. I had different sized rims and tires on the back from the front. You may want to check and make sure your tires are the same size and that you have the same psi in them. Hope this helps.

[muddog321]

No dash lights mean the switch is not powered so see if the connector is off the back of it. The dash switch has 8 volts sent from the TCCM and it monitors return voltage with each mode having a diff resistor so diff return - thats how TCCM knows what mode you selected.

[chevyman69]

all wheels and tires are stock. and i do have lights on the dash, 2wd is lit up and when i push the 4hi the 2wd light stays on and the 4hi blinks then i hear the clicking sound from the tccm about 4 times then the 4hi stops blinking and the 2wd light stays on. i tryed grounding out the 13 pin to see what codes i got, and they only blinked 1 time., and im told that means no codes. i let my wife drive it around today to see if it got any codes and now it doesnt blink at all?

[JaVeRo]

Your 4hi light is not gonna stay on unless the front axle engages. After you put it in 4 hi, ignore the lights and try turning your front driveshaft. If it is locked then the transfer case is engaged and the problem is in the front axle/actuator or the vacuum not getting to it.

James

[chevyman69]

so what your saying is the front axle has to engage before the transfer case engages. i thought it was the other way around

[JaVeRo]

No, what I am saying is that the front axle has to engage before the lights will show that the 4wd is engaged. It is easily posible that the transfer case can engage and the lights not show it.

The switch on the dash tells the transfer case to engage in either 4hi or 4lo. The encoder motor does this. I have never had problems with this part so I can't tell you much about it but others here can.

When the transfer case engages there is a vacuum switch on top of the transfer case with a ball that rides on a cam that the ball gets pushed in. This allows vacuum to the actuator beneath the battery box. Assuming that the vacuum actuator is working right, the vacuum pulls a diapham that pulls a cable connected to the front differential. This cable pulls a mechanism that looks like a clutch fork with a splined collar that slips over the right side drive axle and engages the front differential. On the end of the cable attached to the differential there is a switch with two wires. When the differential is engaged, contact is made in the switch and the 4hi or 4lo light will come on.

I'm not sure but I believe that when the lights are flashing, the TCCM is waiting for a signal (voltage) from the switch on the front differential. When it doesn't get it then it will revert back to the 2hi light but the transfer case is still engaged if the problem was the actuator and not the transfer case.

Turning the driveshaft just tells you if the problem is with the transfer case or the front differential.

James

[chevyman69]

the transfer case is doing nothing, its not shifting, moving or making any noise. thats the only reason i never replaced the axle sensor, i thought the trans case had to shift first to make the front work. im no expert on these. some say if the front sensor is bad then the case wont shift. this i have no idea. now when i had the encoder motor off i tryed to engage the shaft on the case but i couldnt get it to move. now can you move the shaft with the encoder motor off? thanks for you help

[JaVeRo]

Originally Posted by chevyman69

now when i had the encoder motor off i tryed to engage the shaft on the case but i couldnt get it to move. now can you move the shaft with the encoder motor off? thanks for you help

I have never had problems with the transfer case so I know very little about it but if you go up to "Automotive Forums>Chevrolet>Blazer>How To/Technical Info" you will find an excelent article by muddog on how everything works. After reading the first post scroll down to the 7th post for more info on the transfer case in your truck.

Or click here http://www.automotiveforums.com/vbul...d.php?t=572914

James

[BlazerLT]

Vacuum actuator on the front differential is the usual cause of this.

[JoulesWinfield]

Originally Posted by chevyman69

...i thought the trans case had to shift first to make the front work.

You are correct sir. The ball actuated switch on the top of the t-case is what sends vacuum up to the front diff actuator. If the t-case doesnt engage first there is no way to send the vacuum up front.

Are you sure that the new t-case motor is good? You should be able to hear it engage.
There are some electrical checks that you can make to be sure. I would pass along the information that I have but it is for the 1995. Im not sure if retreiving codes is the same for yours but I will give you what I have. Try this at your own risk. I strongly suggest searching around to see if someone else with the same vehicle has pulled codes from theirs before shorting the DLC.

Heres what I have for retreiving codes:
RETRIEVING DIAGNOSTIC TROUBLE CODES
1) Locate Data Link Connector (DLC) near right side of
steering column. Install jumper wire between diagnostic pigtail
(Orange wire at DLC terminal No. 13) and ground.
2) Turn ignition on Observe 4WD elector switch status lamps.
After approximately 3 seconds, status lamp should flash if a DTC is
present. If more than one code is present, the second code will flash
after a 3 second delay. All transfer case DTCs are single digit
numbers. See Fig. 1.
3) Write down all DTCs. After retrieving DTCs. Clear TCCU
memory and repeat procedure. See CLEARING DIAGNOSTIC TROUBLE CODES. If
DTCs return, perform appropriate test. See DIAGNOSTIC CHARTS under
DIAGNOSTIC TESTING.

DTC 1 - TCCM INTERNAL FAULT
1) Turn ignition switch on and off 5 times, waiting 5 seconds
between each cycle. Recheck DTCs. If DTC 1 is present, go to next
step. If no DTC does not return, problem is intermittent.
2) Check circuit 1640 (Orange wire) between fuse panel and
TCCM for open. If open circuit was found and repaired, recheck for
DTC. If open circuit was not found, replace TCCM and recheck for DTC.
DTC 2 OR DTC 1 & 2 - ENCODER FAULT
1) Disconnect transfer case harness connector. Measure
voltage on Brown/White, Red/White, Dark Blue/White, Yellow/Black wires
and ground. If 5 volts exists on each circuit, go to next step. If 5
volts does not exist on each circuit, go to step 3).
2) Measure resistance between Black/White wire at transfer
case harness connector and ground. If resistance is less than 2 ohms,
replace encoder and shift motor assembly. If resistance is greater
than 2 ohms, repair open Black/White wire.
3) Measure resistance of Brown/White, Red/White, Dark
Blue/White, Yellow/Black wires between transfer case harness connector
and TCCM harness connector. If resistance is greater than 2 ohms,
repair open circuit as necessary. If resistance is less than 2 ohms on
all circuits, replace TCCM. Recheck for symptom and DTC.
DTC 3 OR DTC 1 & 3 - MOTOR CIRCUIT FAULT
1) Check 25-amp 4WD fuse. If blown, replace fuse and go to
next step. if fuse is okay, go to step 3).
2) Test drive vehicle and attempt to shift transfer case. if
4WD fuse is blown, go to next step. If fuse is okay, restore
electrical connections and recheck for DTCs and symptom. If DTC does
not return, fault is intermittent.
3) Check transfer case harness connector for corrosion and
damage. Repair if necessary. Replace 4WD fuse it blown. Turn ignition
on. Measure voltage between Black wire and Red wire at shift motor
harness connector while operating 4WD selector switch between 4HI and
4LOW. Voltmeter should fluctuate between positive and negative
voltage. If voltage fluctuates, go to next step. If voltage does not
fluctuate, go to step 5).
NOTE: Ensure transfer case is mechanically sound before proceeding
with next step.
4) Replace transfer case encoder and shift motor assembly.
Restore electrical connections and recheck for DTCs and symptom.
5) Check TCCM harness connectors for corrosion and damage.
Repair if necessary. Turn ignition on. Measure voltage between ground
and TCCM harness connector terminals D14 and D15 (Orange wires). If
battery voltage does not exist, repair open Orange wire between fuse
panel and TCCM. If battery voltage exists, go to next step.
6) Check Black wire and Red wire between shift motor and TCCM
harness connectors for open or short to ground. Repair as necessary.
If Red and Black wires are okay, replace TCCM. Recheck For DTCs and
symptom.
DTC 4 OR DTC 1 & 4 - TCCM RAM/ROM FAULT
1) Turn ignition switch on and off 5 times, waiting 5 seconds
between each cycle. Recheck DTCs. If DTC 4 is present, go to next
step. If no DTC does not return, problem is intermittent.
2) Replace TCCM. Restore all electrical connections. Repeat
step 1). Ensure all DTCs are repaired.