Pinpoint Test A: Four-Wheel Drive (4WD) System Functional Test
- Refer to Wiring Diagrams Cell 34 for schematic and connector information.
Normal Operation and Fault Conditions
The four wheel drive system functional test will isolate and test each sub-system to determine if the subsystem is functioning properly. If a fault is found, additional testing of the suspect sub-system will be required.
When operating in 2H mode, the transfer case clutch is de-energized and both IWE are disengaged. The TCCM may engage the IWE in 2H mode to speed warm up of the front axle fluid in cold weather. The transfer case has clutch drag which can sometimes cause the front driveshaft to spin in 2H mode.
When operating in 4WD modes both IWE s are engaged. In 4H and 4L, the TCCM will move the mode fork in the transfer case to mechanically lock the transfer case in 4WD. In 4L, the TCCM will move the range fork in the transfer case to mechanically lock the transfer case in 4L range.
DTC Fault Trigger Conditions
DTC Description Fault Trigger Condition TCCM C1979:00 IWE Solenoid Circuit Failure: No Sub Type Information This DTC sets when the TCCM commands 4WD operation, but the front wheel speeds do not match rear wheel speeds within a calibrated time. Possible Causes
- ATCM
- IWE
- Transfer case
- Front Axle
- Front Halfshaft
NOTE: 4X4 High and 4X4 Low are not intended for driving on hard/dry surfaces. Using these modes while driving on these surfaces may produce noises like intermittent clunking and should be done for testing purposes only. Using these modes while driving on these surfaces for extended periods of time may damage driveline components. - A1 CHECK THE ATCM (ALL TERRAIN CONTROL MODULE) FOR DTC (DIAGNOSTIC TROUBLE CODE) S
- Enter the following diagnostic mode: ATCM On Demand and CMDTC self-test.
Are any DTC s present?
Yes RESOLVE all ATCMDTC s. REFER to the DTC chart above. No GO to A2 - A2 CHECK THE TCCM (TRANSFER CASE CONTROL MODULE) FOR ON DEMAND OR CMDTC (CONTINUOUS MEMORY DIAGNOSTIC TROUBLE CODE) S
- Enter the following diagnostic mode: TCCM On Demand and CMDTC self-test.
Are any On Demand or CMDTC s present?
Yes If only C1979:00 is present, GO to A3
RESOLVE all other TCCMDTC s. REFER to the DTC chart above.No GO to A3 - A3 CHECK ATCM (ALL TERRAIN CONTROL MODULE) FOR PROPER OPERATION
- Push the individual 4x4 states on the ATCM switch slowly through all positions.
Does each LED illuminate as the corresponding mode is selected?
Yes GO to A4 No CHECK OASIS for any applicable TSB, GSB, SSM, or FSA. If a service article exists for this concern, DISCONTINUE this test and FOLLOW the service article instructions. If no service articles address this concern, INSTALL a new ATCM REFER to: All Terrain Control Module (ATCM) - Vehicles With: Center Console . REFER to: All Terrain Control Module (ATCM) - Vehicles Without: Center Console . - A4 CHECK ATCM (ALL TERRAIN CONTROL MODULE) FOR PROPER OPERATION
Access the TCCM and monitor the 4X4_SWPID- Push the individual 4x4 states on the ATCM switch slowly through all positions.
Does the PID value match each selected mode?
Yes GO to A5 No INSTALL a new ATCM. REFER to: All Terrain Control Module (ATCM) - Vehicles With: Center Console . - A5 CHECK FOR LH (LEFT-HAND) AND RH (RIGHT-HAND) IWE (INTEGRATED WHEEL END) DISENGAGEMENT
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NOTE: The TCCM may command the IWE to engage during 2H operation to warm up the front axle. Ensure ambient temperature is above 32 F (0 C).
With the vehicle in N, position it on a hoist. Ensure straight-ahead steering wheel angle. Raise the vehicle until all 4 wheels are off the ground. REFER to: Jacking and Lifting - Overview .
- Select ATCM mode 2H. There will be a 5 second delay before the IWE is commanded to disconnect.
- Rotate the LH front tire one revolution forward and one revolution backward while observing the LF halfshaft.
- Rotate the RH front tire one revolution forward and one revolution backward while observing the RF halfshaft.
Did both halfshafts remain stationary?
Yes GO to A6 No Install new IWE. REFER to: Integrated Wheel End (IWE) - Vehicles With: 4HI-LOC Torque on Demand Transfer Case/Electronic Shift Transfer Case . GO to A9 -
- A6 CHECK FOR LH (LEFT-HAND) AND RH (RIGHT-HAND) IWE (INTEGRATED WHEEL END) ENGAGEMENT
- Vehicle on hoist with all 4 wheels off the ground
- Select ATCM mode 4H.
- Rotate the LH front tire one revolution forward and one revolution backward while observing the LH halfshaft.
- Rotate the RH front tire one revolution forward and one revolution backward while observing the RH halfshaft.
When the tires were rotated, did the corresponding halfshaft rotate with them?
Yes GO to A7 No INSPECT the halfshafts for damage including inner and outer cv joints and stem to hub nut and REPAIR as necessary. VERIFY the hub nut is torqued to specification and not loose or backed off. If no damage is noted, INSTALL a new IWE. REFER to: Integrated Wheel End (IWE) - Vehicles With: 4HI-LOC Torque on Demand Transfer Case/Electronic Shift Transfer Case . GO to A9 - A7 CHECK FOR FRONT AXLE FUNCTION
- Vehicle on hoist with all 4 wheels off the ground.
- Select ATCM mode 4H.
- Rotate the LH front tire one revolution forward and one revolution backward while observing the LH halfshaft, RH halfshaft and front driveshaft.
- Rotate the RH front tire one revolution forward and one revolution backward while observing the RH halfshaft, LH halfshaft and front driveshaft.
When the tires were rotated, did the opposite halfshaft rotate the opposite direction or did the front driveshaft rotate?
Yes GO to A8 No DISASSEMBLE, INSPECT, and REPAIR the front axle as necessary. REFER to: Front Drive Axle . - A8 CHECK FOR THE CORRECT FRONT AND REAR AXLE RATIO
- Vehicle on hoist with all 4 wheels off the ground
- Select ATCM mode 2WD.
- Rotate a front driveshaft and count the front halfshaft rotations to calculate the installed front axle ratio.
- Rotate a rear wheel and count the rear driveshaft rotations to calculate the installed rear axle ratio.
- Compare the calculated ratios to the listed Axle Ratio under Vehicle ID -> Vehicle Information.
Do the calculated ratios match the listed axle ratio?
Yes GO to A9 No REPLACE the axle with the incorrect ratio. Refer to the appropriate Service Information for the procedure.. - A9 CHECK 4H (FOUR WHEEL DRIVE HIGH) OPERATION
- Select ATCM 4H mode. Ensure straight-ahead steering wheel angle.
- Drive the vehicle on a dry, hard surface, executing turns.
Is wind-up present in turns?
Yes GO to A10 No GO to A11 - A10 CHECK 4L OPERATION
- Select NEUTRAL.
- Verify vehicle speed is less than 5 km/h
- Select ATCM 4L mode.
- Drive the vehicle on a dry, hard surface, executing turns.
Did the transfer case engage low range and was driveline windup present in turns?
Yes The 4WD system is operating correctly at this time. No GO to A11 - A11 CHECK THE TRANSFER CASE OPERATION
- Remove the transfer case shift motor from the transfer case, leaving the wiring connector connected.
- Observe the transfer case shift motor while switching the ATCM mode from 2H to 4H to 2H.
Does the transfer case shift motor rotate during mode transitions?
Yes DISASSEMBLE, INSPECT, and REPAIR the transfer case as necessary. REFER to: Transfer Case - Vehicles With: Electronic Shift Transfer Case . No INSTALL a new transfer case shift motor. REFER to: Transfer Case Shift Motor .