Toyota 4WD. Part-time transfer case feature

© Toyota-Club.Net
Apr 2024

Part-time 4-wheel drive is becoming mainstream for new SUVs on the American market. It is difficult to find any unexpected solutions there, except perhaps the electromagnetic clutch inside the transfer case is worth mentioning.

Transfer case (WF1AM). 1 - planetary gear unit, 2 - input shaft, 3 - H-L shift fork, 4 - L4 position switch, 5 - shifter, 6 - front output shaft, 7 - drive chain, 8 - shift actuator, 9 - rear output shaft, 10 - electromagnetic clutch-type synchromesh mechanism, 11 - 2-4 shift fork, 12 - oil pump.

A transfer case of this design introduced for Tundra UPK5#,USK5# in 2013, and the newer version is used for the current generation Tundra VXKA7#,VXKH7# and Sequoia VXKH8#.

The electromagnetic clutch used for drivelines synchronization when switching from 2WD to 4WD mode.

Electromagnetic clutch-type synchromesh mechanism. 1 - clutch armature, 2 - 2-4 clutch sleeve, 3 - rear output shaft, 4 - front drive sprocket, 5 - lock-up inner hub, 6 - 4WD lock-up hub, 7 - clutch hub, 8 - clutch solenoid, 9 - clutch housing.

The clutch solenoid is attached to the transfer case and produces magnetic force when energized from the 4WD control ECU. The clutch housing is fixed to the rear output shaft via the splined clutch hub and rotates around the clutch solenoid. The clutch armature is always splined to the 4WD lock-up hub.

4WD lock-up hub and 2-4 clutch sleeve are splined to the lock-up inner hub that is fixed to the front drive sprocket. When the 2-4 clutch sleeve moves from 2WD to 4H position, it presses against 4WD lock-up hub via the spring.

The torque transmitted to the front driveline changes depending on effects from electrical synchronization and the movement of the 4WD lock-up hub.

Operation (2WD⇒4WD). 1 - rear output shaft, 2 - lock-up inner hub, 3 - front drive sprocket, 4 - 2-4 clutch sleeve, 5 - 4WD lock-up hub, 6 - clutch armature, 7 - clutch housing, 8 - clutch solenoid, 9 - clutch hub.

- Drive mode is switched from 2WD to 4WD
- 4WD control ECU actuates the clutch solenoid
- Clutch housing is magnetized
- Clutch housing pulls and rotates the clutch armature
- Synchronization of the front driveline and rear driveline is performing
- Transfer shift actuator moves the 2-4 clutch sleeve rearward
- 4WD lock-up hub slides and engages with the clutch hub
- Lock-up inner hub connects with the clutch hub

Toyota WF1AM transfer control system diagnostic trouble codes

P0560 System Voltage
P17A0 Automatic Disconnecting Differential Motor Control Circuit Open
P17A1 Automatic Disconnecting Differential Motor Control Circuit Low
P17A2 Automatic Disconnecting Differential Motor Control Circuit High
P17A4 Automatic Disconnecting Differential Motor Limit Switch Circuit
P17A5 Transfer Synchronization Actuator Circuit Open
P17A6 Transfer Synchronization Actuator Circuit Low
P17A7 Transfer Synchronization Actuator Circuit High
P17A8 Transfer Shift Motor Control Circuit Circuit Open
P17A9 Transfer Shift Motor Control Circuit Low
P17AA Transfer Shift Motor Control Circuit High
P17AB Transfer Shift Motor Position Circuit
P17AC Transfer Shift Motor Limit Switch Circuit
P2772 Four Wheel Drive (4WD) Low Switch Circuit Range / Performance
P279E Four Wheel Drive (4WD) Range Signal Circuit Range / Performance
U0100 Lost Communication with ECM / PCM "A"
U0122 Lost Communication with Vehicle Dynamics Control Module
U0416 Invalid Data Received from Vehicle Dynamics Control Module

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