Allison 3000/4000 Product Families - Electronic Controls

Electronic Controls - Fleet

Allison Electronic Controls work with the hydraulic system to control and continually refine shifts.

• Allison 5th Generation Controls represent the most current control version used with 1000/2000/3000/4000 Product Families Transmissions.

• Previous 3000/4000 Electronic Controls versions include WTEC II, WTEC III, and 4th Generation Controls.

• 5th Generation Controls shares operating theory and similar componentry with previous control system versions.
• Each control system version has its own Troubleshooting Manual, recognize which control system the Transmission utilizes and reference the appropriate manual when diagnosing and making repairs.

• This training is based on the most current version of 5th Generation Controls in production at the time of development.

The Transmission Control Module (TCM) is an onboard computer connected to other Electronic Control components (and the vehicle, by wiring harnesses).

• The wiring harnesses offer J1939 and diagnostic tool interface, and enable connection to other vehicle systems using analog wires.

• The TCM electrically controls solenoids located in the control valve body to determine when and how shifts occur.

• Key factors affecting shift control include Engine speed, Transmission turbine speed, Transmission output shaft speed, and the amount of throttle being requested (throttle position).
• Based on these and other inputs, the TCM energizes and de-energizes solenoids.

• Solenoids direct fluid flow throughout the Transmission to position valves, apply clutches, and provide cooling and lubrication.

A). Transmission Control Module - TCM

The TCM is a microcomputer which monitors all aspects of the Electronic Control system and, among other critical tasks, commands and controls automatic shifts.

• The TCM is externally mounted in the vehicle cab or on the chassis.

• TCMs are manufactured in 12-volt and 12/24-volt models.

• Markings on the TCM include the programmed calibration, Allison part number and TCM serial number.

• TCMs include an integral inclinometer to include road grade data as part of the shift control and optimization processes.

TCMs utilize two levels of software – base programming and calibration.

• Base programming is the term describing basic operational features included with the TCM to perform general tasks.
• Calibration is the term used to describe features which can be utilized for specific vehicle or vocational equipment functions.

B). Throttle Position Signal (TPS)

The TCM monitors the amount of throttle being requested when determining range selection and shift timing.

• Throttle position is most commonly communicated to the TCM on the J1939 datalink.

• But Allison does make available an analog Throttle Position Sensor (TPS).
• The analog TPS can be mounted to the Engine, Chassis or Transmission and sends signals to the TCM through a wiring harness.

• The analog TPS contains a pull actuation cable and potentiometer, one end of the cable is attached to the Engine fuel lever and the other is attached to the potentiometer inside the TPS housing.

• Output voltage from the TPS indicates throttle position which helps the TCM determine shift timing.

• The analog TPS must be correctly installed and adjusted for proper Transmission operation.

C). Speed Sensors

Three sensors provide speed information to the TCM – the input (Engine) speed sensor, turbine speed sensor, and output speed sensor.

• All three sensors utilize variable reluctance design.

• The input speed sensor is externally located on the Transmission torque converter housing.

• 4000 Product Family turbine speed sensors are externally located on the main housing, 3000 Product Family turbine speed sensors are internally located in the control valve module.

• The output speed sensor is externally located on the rear cover or retarder housing, except for 3000 7-speed models, which has the output speed sensor internally located in the transfer case housing.

• The input speed signal is generated by sensing external ribs on the shell of the torque converter pump.

• The turbine speed signal is generated by sensing the splines on the rotating clutch drum.

• The output speed signal on non-retarder, non-drop-box 3000 Transmissions is generated by sensing movement of a tone wheel located on the P3 carrier.

• The output speed signal on retarder-equipped 3000 Transmissions is generated by sensing movement of the retarder rotor.

• The output speed signal on drop-box equipped 3000 Transmissions is generated by sensing movement of the transfer case idler gear.

• The output speed signal on all 4000 Transmissions is generated by sensing movement of the output bearing retention nut.

Comparing turbine and output speeds allows the TCM to determine if the appropriate Transmission range is attained based on operator input and operating conditions.

• Speed sensor information is also used to control the timing of clutch apply pressures, resulting in smooth, controlled shifts.
• Some diagnostic tests compare actual speed sensor information to profiles stored in the TCM memory, DTCs can result if variances exist between actual and stored profile data.

• Speed sensor data is also used by the TCM’s "adaptive" feature which continually monitors and refines shift quality.

D). Solenoids and Control Valve Module

5th Generation Controls include solenoids which direct fluid pressure and flow within the Transmission.

• Solenoids are located in the hydraulic control valve module.

• The control valve module contains a main body assembly and a solenoid valve body assembly, both are mounted to an aluminum channel plate.

• The TCM electrically commands the solenoids to control fluid flow to the clutches.

E). Shift Selectors

Allison 5th Generation Controls shift selectors are electronic, remote-mounted from the TCM, and communicate with the TCM via the CAN1 or CAN2 SAE J1939 communications datalink.

• A variety of selector configurations are available for different vocational applications and operational needs.

• Along with providing operator range selection signals, the shift selector can also be used to access the control system diagnostic and Oil Level Sensor modes.

• In addition to the J1939 interface, an analog direction signal wire is connected to the shift selector to enable limited operation in the event of a J1939 communication failure.

Some key shift selector display patterns include:

• Select side flashing – indicates a requested shift is being inhibited.

• Select side blank – indicates the presence of an active DTC, typically accompanied by the Monitor side displaying the range in which the Transmission is locked.

• Both sides blank – indicates a lack of power to the selector or a J1939 failure.

• All segments illuminated on both sides for more than 12 seconds – the TCM has not completed initialization, typically accompanied by a DTC (depending on calibration), a text message may also be displayed.

• Double cat-eyes – indicates a J1939 failure which is always accompanied by a DTC.

Depending on TCM programming, the selector Mode button may be used to change Transmission shift characteristics or activate programmed features.

• For example, the Mode button may be programmed so that the operator can choose between Economy or Performance shift schedules.
• Another example – the Mode button may be programmed to enable the vehicle’s PTO system.
• The Mode button is also used to navigate display messages when in the OLS, prognostics or diagnostic modes.

F). Wiring Harnesses

Electronic control components are connected using external and internal wiring harnesses.

• Harness configurations can vary depending on the installation and vehicle type.
• An external harness connects the TCM, internal Transmission components and external vehicle system components.

• The internal harness is located inside the control valve module and provides connections between the TCM and solenoids, pressure switches and sensors.

Vehicle Interface describes the connections between vehicle systems and the Transmission electronic control system.

• Mandatory interface connections (for example, power and ground) are required for basic Transmission operation.

• Optional Input and Output functions are programmed features which can control specific equipment and Transmission operation depending on detected conditions or operator commands, Allison Tech Data (available on the Allison Hub) provides detailed Package and Group information as well as Input/Output function descriptions and interface wiring schematics.

• Technicians need to be aware of programmed Input/Output functions which may impact how the Transmission or equipment operate, what may seem like an operational issue may actually be an active Input/Output function performing as designed.

A vehicle interface module (VIM) is available from Allison for simplifying mandatory system connections, including power, ground and ignition signal.

• The VIM contains relays, fuses, and connection points which can be used to simplify mandatory interface and connections for input/output features not interfaced on the J1939 datalink.
• VIMs are available for both 12-volt and 24-volt systems.

The Troubleshooting Manuals include harness connector repair procedures.

G). Shift Inhibits

Some “built-in” shift inhibits are included with the TCM programming and logic.

• Engine Speed Inhibit prevents an attempt to shift from Neutral to any moving range if the Engine speed is above idle (900 rpm for non-emergency vehicles and 1260 rpm for emergency vehicles).
• Direction Change Inhibit prevents a direction change from Drive to Reverse or from Reverse to Drive if output speed or throttle percent are above pre-determined limits.
• Auxiliary Function Range Inhibit is an Input/Output feature that can prevent shifts out of Neutral when auxiliary equipment is in operation.
• The Select side of the shift selector display flashes when shift inhibits are active.

Allison DOC® includes a Shift Inhibits grid that indicates status of any shift inhibits.

• Allison DOC® also has the ability to run a report showing currently active shift inhibits and any shift inhibits that may have been active since the last time DTCs were cleared.

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