MP143 Transfer Case - Service Information: Overview Dodge Nitro I

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Available with both manual and automatic transmissions, the MP143 single-speed, part-time transfer case is used in Nitro's new Part-Time Four-Wheel Drive System. Two-wheel drive and four-wheel drive modes are electronically controlled via a switch in the center console. Either mode can be selected at any time. The MP143 transfer case works with standard-equipment Traction Control and ESP (Electronic Stability Program) features to provide enhanced traction and stability on low-traction surfaces.

1. Two operating positions: 2WD and 4Lock controlled via a switch in the center console.
2. For temporary conditions that require extra traction such as snow or mud, the part-time 4Lock mode locks the main shaft and drive sprocket hub, making the front and rear wheels rotate in unison and offering maximum traction.
3. Enhanced traction and stability provided by Traction Control and ESP working in tandem with part-time four-wheel-drive. Traction Control and ESP provide resistance to any wheel that is slipping to allow additional torque transfer to wheels with traction.
4. Robust design and sealing for reliability.
5. Maintenance free.

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In 2WD mode, the front axle and driveshaft turn freely while power is sent to the rear axle and wheels. In 4Lock mode, the front and rear wheels rotate in unison, resulting in remarkable traction. Because this is a part-time system, it locks the front and rear drive shafts together. Therefore, it can only be used on slippery or loose surfaces like ice, gravel, or rugged terrain. The standard-equipment ESP, which combines ABS, Traction Control, and Electronic Roll Mitigation, enhances traction by modulating torque among all wheels as necessary - providing resistance to any wheel that is slipping while allowing torque to flow to the wheels with traction.

The MP143 transfer case also has an analog shift actuator mounted on the rear of the transfer case that communicates with the switch through the CAN-bus network.

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1. Raise vehicle. CAUTION: Do not allow propeller shafts to hang at attached end. Damage to joint can result.
2. Remove the front and rear propeller shafts. Refer to «REMOVAL»(ref-306145-S17464238962008120900000) .
3. Support transmission with jack stand.
4. Remove rear crossmember and skid plate, if equipped.
5. Disconnect transfer case vent hose (4).
6. Disconnect the transfer case shift motor electrical connector and position the harness aside.
7. Disconnect the wiring connector from the shift motor, if necessary.
8. Support transfer case with transmission jack and secure with chains.
9. Remove nuts (2) attaching transfer case (1) to transmission (3).
10. Pull transfer case and jack rearward to disengage transfer case form the transmission case.
11. Remove transfer case from under vehicle.

DESCRIPTION-SHIFT MOTOR

A rotary switch on the instrument panel controls the Electric Shift on-the-fly transfer case mode selection. Switch positions are labeled 2WD and 4 LOCK, shown in illustration by an indicator in the instrument cluster. The switch uses resistive multiplexing to signal the Front Control Module (FCM) which mode to select.

OPERATION-SHIFT MOTOR

The FCM, which receives its operating signal from the switch via the Cab Compartment Node and the CAN intra-vehicle communications network, operates an electric motor that shifts the transfer case. The FCM obtains additional data necessary for operation and provides diagnostic outputs via the CAN network. Diagnostic outputs include fault codes and the ability to "read" switch position and position sensor output. For test purposes, a diagnostic tester such as the MDT II or the MOPAR Diagnostic System can operate the motor. A warning lamp in the instrument cluster illuminates if a malfunction in the electric-shift system occurs.

A motor and encoder (position sensor) replace a lever on the shaft that shifts the transfer case. When a shift is requested, the motor turns the shaft until the sensor indicates that the correct angular position has been reached. To prevent the transfer case from making unintended shifts, the switch must be in position for 0.25 seconds before a shift will take place. A shift can take up to 1.25 seconds from the time that the switch is moved for full travel. If the shift is not completed in the appropriate time, the module will repeat the action up to five times. Misalignment of the gears in the transfer case may block a shift, which will be detected by a sensor; the motor will then reverse and try again to complete the shift. Blockage can occur if the vehicle is stationary when the shift is initiated, but if the vehicle is moving as recommended when the shift is initiated, then blockage is unlikely. If the shift is not completed after five attempts, the cluster indicator will flash and the driver will have to return the switch to its former position and repeat the operation.