Circuit Protection - Power In

Circuit Protection -- Power In

The battery feed circuit, through a circuit breaker, provides memory
capability for the electronic control module.

Ignition RUN feed circuit, through a fuse, provides power for the switches
and the electric shift motor.

The circuit provides power for nighttime illumination of the switches
located in the instrument panel.




Power In

Power is supplied to the system at three points (P1, P2 and P3 in
schematic).

^ P1. This is a direct connection to the battery. This power drives the electric shift control motor and provides current to the instrument cluster lamps. This circuit goes to ground G1.

^ P2. The electronic shift control module is tied into the ignition circuit. This circuit provides power to the computer and goes to ground G2.


^ P3. Nighttime illumination is provided by a connection to the vehicle's nighttime illumination circuit, which goes to ground G3.

The electronic shift control module directs power depending on the position
of the control switches. In the schematic, you will notice that inputs and
outputs to and from the shift module are labeled A, B or C. A circuits are
power circuits, B circuits are data circuits from sensors and C circuits
are activating switch and related lamp circuits.

The B circuits supply data from three sources: The speed sensor, the motor
position sensor and either a park/neutral position switch (for automatic
transmissions) or a clutch pedal position switch (for manual
transmissions).

The speed sensor is important because the vehicle must be stopped for a
shift into or out of 4L. The shift module won't make the shift if the
vehicle is moving. The shift module also won't make a shift to 4L or back
unless an automatic transmission is in neutral or the clutch is depressed
on a manual transmission.

The motor position sensor indicates the position of the shift motor shaft.
This shaft turns through approximately 270� and should stop at three
indexed points, 2H, 4H and 4L. The shift control module needs to know where the shaft is before making a new shift. When this sensor isn't functioning properly or the motor stops slightly off location, the shift control module may become "confused."











The C circuits involve the switches on the vehicle's control panel. When
everything is working properly, activating a switch will result in either a
shift from 2H to 4H or back, or a shift from 4H to 4L or back. The default
operating mode is 2H. This means that in the absence of other instructions,
the shift control module will assume that the vehicle should be in 2H. If
there is a failure in the system during shifts or engine start up, it will
default the vehicle to 2H and permit continued operation.