Up To Standards
- Author: Mike Weinberg
- Subject Matter: MP3023 T-case
- Issue: Complex electronics
The MP3023 is an active automatic transfer case that is found in a wide variety of vehicles. This unit will be found in GM trucks 2007-13, Jeep Grand Cherokees 2011-19, and in Dodge Durangos 2010-up. We will be discussing the Jeep version here, which has very sophisticated control electronics. The transfer cases are basically all the same across the product line, but there are considerable variations in the electronics, which will make diagnostics outside of the transfer case a learning experience.
In the Grand Cherokee the 3023 is called Select Trac II, and Quadra Trac II. This is an on demand, two speed, active four-wheel-drive transfer case. There are two operating modes, 4WD Auto, which requires no input from the driver to monitor all four wheels, speeds and bias torque as needed to eliminate any slippage. In the 4WD Low mode, both drive shafts are locked together with a 2.72 planetary gear reduction for off-road-only use. Never drive these units on dry pavement in low range to avoid internal damage to the transfer case. As usual with any clutch-operated active transfer case tire sizes and pressures must be the same.
This means measuring tire circumference on all four wheels before starting any diagnostic work, unless you like incredibly time-wasting work. The transfer case uses a complex console switch that is capable of engaging the 4WD Auto and Low modes as well as specifying various road and weather conditions. The transfer case controls originate in the Drive Train Control Module (DTCM) and communicate with the Controller Area Network (CAN) C Bus. In the program is a very sophisticated algorithm designed to compensate for any type of road conditions that compare wheel speeds on all four wheels and work the traction control and electronic stability program with the 4WD system. Add to that the brake traction-control system, which will add braking at individual wheels to control the vehicle speeds in turns and other weather conditions to protect the driver from their inherent lack of skill.
The system will read road speed and steering angle to know that the driver is going too fast for conditions and pinch brakes accordingly to put the vehicle on a survivable path of direction. These vehicles can be driven with just one wheel if needed, and the driver is unaware that modern technology has prevented a crash or off-road excursion. On the console switch there is a pin push mode for obtaining neutral so that the vehicle can be flat towed.
The 3023 features a separate shift motor and encoder. The shift motor working with a geared shift shaft and cam applies the clutch pack as commanded. There is also a barrel cam that will engage the low range mode when needed. The clutch cam operates twin levers that contain a ball-and-ramp system to engage the clutch pack as needed. These are basically simple units that have some tricky disassembly and assembly issues that will require you to take advantage of the service manual (Figure 1).
For instance, there is a shift motor seal that must be carefully removed from the shift shaft during disassembly. The worm-shaft snap ring will then come out and the worm shaft can be removed by turning it clockwise until the threads release and it can be removed before trying to split the cases (Figure 2).
With the cases split the worm drive gear can be removed and then the clutch cam. Make a note to mark the upside during removal to properly re-orient the components on assembly. When reinstalling the separate encoder onto the case, you must align the alignment mark on the encoder shaft with the alignment mark on the case to properly orient the shift shaft to the encoder (Figure 3).
Both marks should be facing 6 o’clock when properly positions. Failure to do so will have the encoder unable to know where the shift shaft is positioned. These units are equipped with an electric brake on the shift motor to keep the motor in the selected mode unless otherwise commanded. Early units had Bosch motors that suffered more than normal failures and have been replaced with a newly designed motor from Daewoo. The newly designed motor will replace the older design. There is a motor relearn procedure that will need to performed on any motor replacement.
The mechanics of these transfer cases is relatively simple, but the electronics is very complex. Get the service manual and go down the diagnostic trees to solve a problem, which is much easier than trying to become Christopher Columbus.