Diagnostic Strategies

The AW4 Transmission test and support functions (State Display) can be selected from menus accessed through the Main Menu (you MUST select either a 2.5L XJ or 4.0L XJ in order to be given the option of selecting the AW4 Transmission test or AW4 State Display). As with all other tests and State Displays, the F3 key will provide HELP at any time.

There are three (3) functions related to testing and one (1) adjustment procedure with the AW4 Transmission. Test functions include a stationary (in bay) test, a road test, and a State Display. Data necessary for transmission testing is provided through a data stream issued from the Transmission Control Unit (TCU). As with engine testing, the key must be ON for the TCU to transmit data. The Throttle Position Sensor is adjusted by using the DRBII with the voltage probe and a pair of jumper wires.

The stationary test and road test may be run separately or sequentially (stationary test first).

The stationary test monitors for the presence of data, current solenoid faults, switch faults, correct TCU design and calibration levels, and proper function of the TCU. An operator will be directed to perform several mechanical functions including:

- selecting gears,
- operating the mode select switch,
- depressing the brake,
- and depressing the accelerator pedal. Seven asterisks (*******) will be displayed corresponding to throttle positions 1 through 7. By depressing the accelerator, the TPS will sweep through the entire range of positions required by the TCU. A corresponding asterisk will be cleared from the display as each of the throttle positions are sensed by the TCU. Several attempts may be required to clear all of the asterisks from the display, depending on how fast the accelerator pedal is pressed.

The DRBII will indicate whether or not a requested action has been seen by the TCU. If the operator is requested to perform a particular operation, and the TCU does not acknowledge the action, pressing the ENTER key will result in the appropriate fault being displayed.

During the road test, all solenoids and the speed sensor are tested. The operator is directed to accelerate to 55 MPH at light throttle to ensure that the transmission is exercised through all gears and thereby all three solenoids are tested. A test site should be selected where the vehicle can be accelerated slowly and evenly to a speed sufficient to allow all gear transitions, without downshifting, and without braking during the test. A fault sensed with any solenoid or the speed sensor will be displayed.

NOTE: If a fault is sensed by the TCU, the control logic will force a specific solenoid (gear) configuration dependent on the solenoid faulted. Because transmission faults are sensed and displayed one-at-a-time, multiple faults must be identified through retest.