GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1999 🢒 Envoy - 4WD 🢒 Driveline/Axle 🢒 Transfer Case - NVG 236 (Two Speed Automatic) 🢒 Front Axle Will Not Disengage

Object Number: 382173 Size: MF
Transfer Case Control Components
Transfer Case Control Schematics

Circuit Description

The front axle control circuit consists of an electric motor actuator which engages and disengages the front axle. The front axle actuator's motor consists of a permanent magnetic (PM) motor, a worm gear controlled plunger, a front axle switch and an electronic control circuit all within the actuator assembly. The front axle actuator has four circuits connected to it. CKT 241 supplies ignition voltage to the actuator. CKT 2150 provides the ground. CKT 1695 is the front axle switch, and CKT 1570 is the front axle control.

Whenever a shift to AUTO, 4WD, 4HI, or 4LO is requested, the automatic transfer case control module engages the front axle by grounding the front axle control CKT 1570 through a current limiting driver.

Test Description

The number(s) below refer to the step number(s) on the diagnostic table.

  1. This step determines if the scan tool has electronic control of the front drive axle clutch solenoid.

    2.

  2. This step determines if the failure involves the front drive axle clutch solenoid or the front axle switch.

    3.

  3. This step tests for a shorted condition at the front drive axle clutch solenoid.

    4.

  4. This step determines if the front axle engagement is do to a short to ground condition on the ground side of the front drive axle clutch solenoid.

  1. This step determines whether the shorted condition is in CKT 1570 or inside the transfer case shift control module.

    2.

  2. This step tests the controller's ability to sense an open condition at the front axle switch.

    3.

  3. This step tests for a short to power condition in CKT 1695.

    4.

  4. This step tests for a leaking vacuum valve at the front drive axle clutch solenoid.

Front Axle Will Not Disengage

Step

Action

Value(s)

Yes

No

1

Was the Transfer Case Diagnostic System Check performed?

--

Go to Step 2

Go to Transfer Case Diagnostic System Check

2

  1. Turn the ignition ON, engine ON.
  2. Place the vehicle into 2WD mode.
  3. Connect a Scan Tool in order to monitor the Front Axle Switch status.
  4. Use the Scan Tool to disengage the front axle.

Does the Front Axle Switch status change from LOCKED to UNLOCKED?

--

Go to Step 14

Go to Step 3

3

Inspect the front axle to determine if it is mechanically engaged to the transfer case.

Is the front axle mechanically engaged to the transfer case?

--

Go to Step 4

Go to Step 7

4

  1. Turn the ignition OFF.
  2. Disconnect the connector at the front drive axle clutch solenoid.
  3. Turn the ignition ON, engine ON.
  4. Use the Scan Tool in order to monitor the state of the Front Axle Switch.

Does the state of the Front Axle Switch change from LOCKED to UNLOCKED?

--

Go to Step 5

Go to Step 10

5

  1. Turn the ignition ON, engine OFF.
  2. Use the Scan Tool in order to command the front drive axle clutch solenoid OFF.
  3. Connect a J 39200 Digital Multimeter DMM and measure the resistance between the front drive axle clutch solenoid harness connector terminal B and ground.

Is the resistance reading within the value specified?

OL

Go to Step 15

Go to Step 6

6

  1. Disconnect connector C1 at the transfer case shift control module.
  2. With the J 39200 DMM still connected, measure the resistance between the front drive axle clutch solenoid harness connector terminal B and ground.

Is the resistance reading within the value specified?

OL

Go to Step 14

Go to Step 13

7

  1. Turn the ignition ON, engine OFF.
  2. Use the Scan Tool in order to continue to monitor the status of the Front Axle Switch.
  3. Disconnect the connector at the front axle switch.

Does the status of the Front Axle Switch change from Locked to Unlocked?

--

Go to Step 16

Go to Step 8

8

  1. Turn the ignition ON, engine OFF.
  2. Connect a J 39200 DMM between the front axle switch harness connector terminal B and ground.

Is the voltage reading within the value specified?

0 V

Go to Step 14

Go to Step 9

9

Disconnect connector C1 at the transfer case shift control module.

Is the voltage reading within the value specified?

0 V

Go to Step 14

Go to Step 12

10

  1. Turn the ignition ON, engine ON.
  2. Disconnect the vacuum source from the front drive axle clutch solenoid.

Does the Front Axle Switch status change from LOCKED to UNLOCKED?

Go to Step 15

Go to Step 11

11

Inspect the front axle for a mechanical failure.

Is there any mechanical failures?

--

Go to Step 17

Go to Step 15

12

Repair short to voltage in CKT 1695. Refer to Wiring Repairs in Wiring Systems.

Is the repair complete?

--

Go to Step 18

--

13

Repair short to ground in CKT 1570. Refer to Wiring Repairs in Wiring Systems.

Is the repair complete?

--

Go to Step 18

--

14

Replace the transfer case shift control module. Refer to Transfer Case Shift Control Module Replacement .

Is the action complete?

--

Go to Step 18

--

15

Replace the front axle actuator. Refer to Front Drive Axle Actuator Replacement .

Is the action complete?

--

Go to Step 18

--

16

Replace the front axle switch.

Is the action complete?

--

Go to Step 18

 

17

Repair mechanical failure inside the transfer case. Refer to Transfer Case Mechanical System Diagnosis .

Are the repairs complete?

 

Go to Step 18

 

18
  1. Ensure that the ignition is OFF.
  2. Properly mount and reconnect all previously disconnected ATC components.

Have all the ATC components been reconnected and properly mounted?

--

Go to Step 19

--

19

Clear all the ATC DTCs.

Have all the ATC DTCs been cleared?

--

Go to Transfer Case Diagnostic System Check

--