94-95 Model

This Diagnostic Trouble Code (DTC) flashes the "CHECK TRANS" Indicator and sets the Backup Mode.




Circuit Description
- The Band Apply Solenoid is a normally open Solenoid which controls the flow of fluid for brake band application. The Transmission Control Module (TCM) uses Pulse Width Modulation (PWM) and changes the duty cycle to control the Solenoid. The TCM turns the Solenoid "ON" (energized) and "OFF" (de-energized) at a constant frequency. The length of time the Solenoid is energized during each "ON"/"OFF" cycle is called the pulse width. By varying or "modulating" the pulse width, the Solenoid output pressure is changed. Since the Solenoid is normally closed, increasing the pulse width increases the duty cycle and decreases the output pressure. PWM control provides smooth band application without an accumulator. The band is only applied in first and second Gears.
- In the event of an electrical failure (open), the Solenoid regulates at the maximum oil flow (0% duty cycle).
- The Solenoid is activated by a current. This current is produced by applying a voltage to one side (the High side) and a ground to the other side (Low side).
- The High Side Driver (HSD) is a circuit of the TCM that acts as a switch between the Solenoid and the supply voltage. The high side of the Solenoid is permanently supplied with voltage, except in Backup Mode or when Ignition is "OFF" the HSD is turned "OFF".
- The TCM continually monitors the Solenoid connection to its Low Side Driver (LSD) for either low or high voltage. The LSD is a circuit of the TCM that acts as a switch between the Solenoid and ground. When the Solenoid is commanded ON the TCM is switching the Solenoid to the ground.
- There are two tests of the LSD: when the Engine is cranked (DTC 82) and when the Ignition is turned "ON" (DTC 34).
- When the Ignition is turned "ON", and before the Engine is cranked, the TCM activates the shift Solenoids (1-2/3-4, 2-3 and Band) to check for short circuits or open circuits. To do so the Gear is set to 4th, 3rd, 1st, 1st with band apply, 4th with no HSD. Each one of the 5 tests requires 0.15 seconds. If the Engine is cranked before the end of all tests, the remaining tests are not done.

Diagnostic Aids
- This diagnostic is an electrical test done by the TCM.

- Detection Conditions:
a. The Solenoid Low side connected to TCM Terminal A9 is shorted to ground or open.
b. The test is only done when Ignition is "ON".
c. Engine speed is less than 480 rpm (not cranked) and output speed equals 0 rpm.
d. The condition needs to be present for 0.15 to 0.75 seconds after Ignition Switch is "ON".

- Action After The Detection Time:
- Backup Mode.

- Recovery Conditions:
- To recover do an Ignition Cycle.





DTC 34 / Flow Chart