Description And Operation: Operation
The 948TE transmission includes:
- 9 forward gears for enhanced performance and fuel economy.
- A compact design for ease of packaging.
- high efficiency in all gears and speeds thanks to nested carriers, dog clutches, and advanced hydraulic control unit architecture.
The 948TE's wide ratio spread brings outstanding launch characteristics, smooth, indecipherable transfer between gears, and fuel efficiency.
The launch ratios:
- In Trailhawk models (4.334 final drive ratio), first gear is only used when the 4 wheel drive low range is selected. First gear is held in this position and provides the low range gear reduction. There is no reduction in the Power Transfer Unit (PTU). When not operating in 4 wheel drive low range, the vehicle launches in second gear.
- The shorter steps between gears translates to extremely manageable "bump and shudder-free" transitions and enhanced noise/vibration characteristics.
- Higher gears - in the seventh, eighth, and ninth transitions, relate to lower engine speeds, and enhanced fuel efficiency.
The transmission name indicates key characteristics:
- The numeral "9" indicates that the transmission has nine forward gear speeds.
- The numeral "48" indicates the transmission torque capacity of 480 Newton meters.
- The "T" indicates that the transmission is transverse-mounted.
- The "E" indicates that the transmission is electronically controlled.
| Gear | Ratios |
| 1 | 4.70:1 |
| 2 | 2.84:1 |
| 3 | 1.91:1 |
| 4 | 1.38:1 |
| 5 | 1.00:1 |
| 6 | 0.81:1 |
| 7 | 0.70:1 |
| 8 | 0.58:1 |
| 9 | 0.48:1 |
| Reverse | 3.81:1 |
| Spread | 9.79:1 |
| Final Drive * | Final drive ratios will vary depending on powertrain applicability |
| Maximum Shift Speed | 6500 RPM |
| Torque Converter | 242 mm (9.531 in.) |
| SHIFT SOLENOID | A | B | C | D | E | F | RATIO | |
|---|---|---|---|---|---|---|---|---|
| GEAR | 1st | X | X | X | 4.700 | |||
| GEAR | 2nd | X | X | X | 2.842 | |||
| GEAR | 3rd | X | X | X | 1.909 | |||
| GEAR | 4th | X | X | X | 1.382 | |||
| GEAR | 5th | X | X | X | 1.000 | |||
| GEAR | 6th | X | X | X | 0.808 | |||
| GEAR | 7th | X | X | X | 0.699 | |||
| GEAR | 8th | X | X | X | 0.580 | |||
| GEAR | 9th | X | X | X | 0.479 | |||
| GEAR | NEUTRAL/PARK | X | X | |||||
| GEAR | REVERSE | X | X | X | 3.805 | |||
| DEFAULT GEAR | 4th | X | X | 1.382 | ||||
Differential and Ring Gear
The ring gear is bolted to the differential housing. The final drive pinion transmits power to the ring gear. Opposing tapered roller bearings support the housing. A shim located under the case side bearing race provides bearing preload adjustment.
The final drive of the transmission includes three gear assemblies: the output gear assembly, the transfer gear assembly, and the differential/ring gear assembly. The P4 carrier transmits power to the output gear through splines on the side of the output gear. The output gear is retained on the output gear support with a spanner nut. Power from the output gear is transmitted to the transfer gear assembly via the driven transfer gear.
Transmission Fluid Pressure Sensor
The transmission fluid pressure sensor is mounted to the valve body and monitors the dog clutch hydraulic exhaust circuit. The sensor reacts to the pressure changes that occur during dog clutch engagement and disengagement.
Transmission Fluid Temperature Sensor
The transmission temperature sensor is part of the transmission pass-through wiring harness. The TCM uses the sensor to monitor transmission oil temperature.
Speed Sensors
The input and output speed sensors are part of a single assembly located under the valve body. The speed sensors are active digital sensors. The input speed sensor uses the E clutch housing as a reluctor, and the output speed sensor uses the transfer gear.
TRS
The TRS is a non-contact Hall-effect sensor with multiple signal outputs.
Transmission Shifter
- The shifter assembly incorporates an electronic control module called an Electronic Shifter Module (ESM). The ESM communicates with the TCM and other modules on the CAN-C bus.
- The transmission includes a manual valve (used only for limp home mode operation) with a mechanical cable between the shifter and the transmission. The Park system is operated mechanically via this shifter cable.
- The ESM processes requests from the TCM to open or close the Brake Transmission Shifter Interlock (BTSI) solenoid located in the shifter.
- The TCM receives information on the gear shift lever position from the ESM.
Valve Body
Valve body function is directed by the TCM. There is a solenoid for each of the six clutches, one for TCC, one for system pressure and a "limp home mode" solenoid. If a fault occurs with the transmission, the TCM may de-energize all solenoids. When all of the solenoids are de-energized, the transmission operation is limited to Fourth gear, Reverse, Neutral and Park due to the presence of the manual valve.
TCM
The TCM regulates the amount of hydraulic pressure used to engage the clutches and the TCC, in addition to directing hydraulic pressure to engage or release any given clutch for any given required gear.
The TCM will actuate the valves via solenoids based on the position of the shifter, transmission fluid temperature, engine operating conditions, traction conditions and driver demands.
During a shift, the TCM will actuate the solenoids to match the gear ranges to the optimal torque range of the engine based on the position of the accelerator pedal, shifter and vehicle speed as determined by the Powertrain Control Module (PCM) based on input from the VSS and ABS module.
Due to the complexity of the 948TE transmission control system, always refer to the transmission electrical/electronic diagnostics in this service information when attempting to diagnose transmission problems.
Some examples of
Direct Inputs
to the TCM are:
- Battery (B+) voltage
- Ignition Status
- TRS
- Cruise Control Switch
- Throttle Position
- Body Control Module (BCM)
- Shifter Position
- Transmission Temperature Sensor
- Input Speed Sensor
- Output Speed Sensor
- Pressure Sensor
Some examples of
Indirect Inputs
to the TCM are:
- Torque Reduction Confirmation
- Engine Coolant Temperature
- Scan Tool Communication
Based on the information received from these various inputs, the TCM determines the appropriate shift schedule and shift points, depending on the present operating conditions and driver demand. This is possible through the control of various direct and indirect outputs.
Some examples of TCM
direct outputs
are:
- Solenoids
- Torque Reduction Request
Some examples of TCM
indirect outputs
are:
- Transmission Temperature
- PRNDL Position
In addition to monitoring inputs and controlling outputs, the TCM has other important responsibilities and functions:
- Storing and Selecting Appropriate Shift Schedules
- System Self-diagnostics
- Diagnostic Capabilities (with scan tool)