Mechanics

CHEVY 4 WHEEL DRIVE

2001 Chevrolet Blazer

2001 Chevy Blazer 6 cyl Four Wheel Drive Automatic 110000 miles

My Blazer is stuck in 4 low. If I push the button
for 2 wheel it flashes then goes back to 4 low. I have checked the relay wiring and also have disconnected the
negative cables to try and reset computer. No luck.
I was told that the majority of the time it is the actuator as they have a history of going out before the
vacuum switch. Is there a way to tell which it is without having to spend 70 bucks for a diagnostics. Or is there possibly a fuse?

Thanks
Don
Avatar
ShadowStryder
May 11, 2010.



Try this 1st
start engine
step on the brakes
place shifter in N position
push the 4 hi or 2

BMRFIXIT
May 11, 2010.
Have done that, sometimes it will go into 2 most of the time it won't. But even when it does it stays for about
2-3 seconds and goes back to 4L. When it does try to
shift I can here the relay clicking. Don't know if that indicates the relay is bad or not.

Tiny
ShadowStryder
May 11, 2010.
TRANSFER CASE SHIFT CONTROL SWITCH INOPERATIVE OR 4 LOW INDICATOR STUCK ON
Circuit Description
The transfer case shift control switch circuit consists of three normally open switches. From the 4WD fuse the switch is supplied with ignition 3 voltage. When one of the switches is pressed, current travels through the switch to its corresponding signal circuit and to the transfer case shift control module. The transfer case shift control module continuously monitors the switch inputs to determine whether the 2HI, 4HI, or 4LO buttons have been selected by the driver.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
2. This step tests the functionality of the transfer case shift control switch buttons.
3. This step tests the transfer case shift control switch for proper function.
4. This step tests the individual switch signal circuits.
5. This step tests the transfer case shift control switch ignition 3 circuit for proper voltage.
6. This step tests the transfer case shift control switch for proper function.
8. This step determines if the vehicle is equipped with an automatic or manual transmission.
9. This step tests the A/T shift lock switch supply voltage circuit for proper voltage.
10. This step repairs an open or high resistance in the A/T shift lock switch supply voltage circuit.
11. This step tests the suspect switch signal circuit for an open or high resistance.
12. This step tests the 4WD fuse for an open.
13. This step repairs an open in the transfer case shift control switch ignition 3 voltage circuit.
14. This step tests the 4WD fuse to determine if it re-blows.
15. The step tests the transfer case shift control switch ignition 3 voltage circuit and the transfer case shift control switch signal circuits for a short to ground.
NOTE: For transfer case schematics refer to TRANSFER CASE CONTROL SCHEMATICS.

Transfer Case Shift Control Switch Inoperative
IMPORTANT: The transfer case shift control module is not a class 2 device, and therefore a scan tool can not be utilized on this transfer case.

Did you perform A Diagnostic System Check - Transfer Case? If yes, go to step 2. If no, go to DIAGNOSTIC SYSTEM CHECK - TRANSFER CASE.
Start the engine. Place the transmission into NEUTRAL, or depress the clutch pedal on manual transmission applications. Set the park brake. Depress each of the shift control switch buttons. Are all of the buttons on the shift control switch working properly? If yes, go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. If no, go to step 3.

Is only one button on the shift control switch inoperative? If yes, go to step 4. If no, go to step 5.

4-Turn ON the ignition with the engine OFF. Connect one end of a DMM to ground. At the back of the shift control switch, back probe the suspect switch signal circuit while pressing it's corresponding switch. Does the voltage measure near B+? If yes, go to step 11. If no, go to step 16.

5-Turn ON the ignition, with the engine OFF. Test the shift control switch ignition 3 voltage circuit for proper voltage. Does the voltage measure near B+? If yes, go to step 6. If no, go to step 12.

6-Connect one lead of a DMM to ground. At the back of the shift control switch, back probe each of the signal circuits while pressing their corresponding switch. Does the voltage measure near B+ for each of the circuits? If yes, go to step 8. If no, go to step 16.
7-Test the 2 HI Switch Signal, 4 HI Switch Signal, and 4 LOW Switch Signal circuits for a short to battery positive. Did you find and correct the problem? If yes, go to step 18. If no, go to step 8.

8-Is this vehicle equipped with an automatic transmission? If yes, go to step 9. If no, go to step 17.
9-Turn OFF the ignition. Disconnect the connectors at the transfer case shift control module. Connect one lead of a DMM to ground. At the harness side of the transfer case shift control module connector, connect the other lead of the DMM to the A/T shift lock switch supply voltage circuit. Turn ON the ignition, with the engine OFF. With the vehicle in NEUTRAL, measure the voltage at the A/T shift lock switch supply voltage circuit. Does the voltage measure near B+? If yes, go to step 17. If no, go to step 10.

10-Test for an open or high resistance in the A/T shift lock switch supply voltage circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? When complete, go to step 18.
11-Turn OFF the ignition. Test the suspect selector switch signal circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? If yes, go to step 18. If no, go to step 17.

12-Test the 4WD fuse for an open. Was the fuse open? If yes, go to step 14. If no, go to step 13.

13-Repair an open in the shift control switch ignition 3 voltage circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you complete the repair? When complete, go to step 18.

14-Replace the 4WD fuse. Take the vehicle for a test drive. Place the transmission into NEUTRAL, or depress the clutch pedal on manual transmission applications. Set the park brake. Press each of the shift control switch buttons. Retest the 4WD fuse for an open. Did the fuse blow again? If yes, go to step 15. If no, go to step 18.
15-Test the shift control switch ignition 3 voltage circuit and the selector switch signal circuits for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you complete the repair? When complete, go to step 18.

16-Replace the shift control switch. Refer to Transfer Case Shift Control Switch Replacement. Did you complete the replacement? When complete, go to step 18.
17-Replace the transfer case shift control module. Refer to Transfer Case Shift Control Module Replacement. Did you complete the replacement? When complete, go to step 18.
18-Operate the vehicle within the conditions for causing the symptom as specified in the supporting text. Does the symptom re-occur? If yes, go to step 2. If no, system is okay.

BMRFIXIT
May 12, 2010.