Pinpoint Test A: Four-Wheel Drive (4WD) System Functional Test
- Refer to Wiring Diagrams Two Wheel Drive/Four Wheel Drive Systems
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 unlocked. The TCCM may engage the IWE in 2H mode to speed warm up of the front axle fluid. The transfer case has certain amount of clutch drag which can cause the front driveshaft to spin in 2H mode.
When operating in 4WD modes both IWE are locked. In 4A, the TCCM will apply the clutch when needed to control wheel slip. 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 Sources
- ATCM
- IWE
- Transfer case
- 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, but does not damage driveline components.
- A1 CHECK THE ATCM (ALL TERRAIN CONTROL MODULE) FOR DTC (DIAGNOSTIC TROUBLE CODE)
- Enter the following diagnostic mode: ATCM On Demand and CMDTC self-test.
Are any DTC present?
Yes RESOLVE all ATCMDTC. REFER to the DTC chart above. No GO to A2 - A2 CHECK THE TCCM (TRANSFER CASE CONTROL MODULE) FOR DTC (DIAGNOSTIC TROUBLE CODE)
- Enter the following diagnostic mode: TCCM On Demand and CMDTC self-test.
Are any DTC present?
Yes If only C1979:00 is present, GO to A3
RESOLVE all other TCCMDTC. REFER to the DTC chart above.No GO to A3 - A3 CHECK ATCM (ALL TERRAIN CONTROL MODULE) FOR PROPER OPERATION
- Rotate the ATCM rotary knob slowly through all positions.
Does each LED illuminate as the coresponding mode is selected?
Yes GO to A4 No INSTALL a new ATCM - A4 CHECK ATCM (ALL TERRAIN CONTROL MODULE) FOR PROPER OPERATION
- Access the TCCM and monitor the 4X4_SWPID
- Rotate the ATCM rotary knob 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 AND RH 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.
With the vehicle in N, position it on a hoist. Raise the vehicle until all 4 wheels are off the ground. REFER to: Jacking and Lifting - Overview .
- Select ATCM mode 2H
- 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) . . -
- A6 CHECK FOR LH AND RH 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.
Did both halfshafts rotate?
Yes GO to A7 No Install new IWE. REFER to: Integrated Wheel End (IWE) . - A7 CHECK 4H OPERATION
- Select ATCM 4H mode.
- Drive the vehicle on a dry, hard surface, executing turns.
Is wind-up present in turns?
Yes GO to A8 No GO to A9 - A8 CHECK 4L OPERATION
- Select NEUTRAL.
- Verify vehicle speed is less than 3 mph (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 A9 - A9 CHECK THE TRANSFER CASE SHIFT MOTOR 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 .