Dodge R1500 1999 Service Manual page 221

The OD (Overdrive) OFF switch is located on instrument panel,
to the right of steering column. The OD OFF switch controls overdrive
operation by delivering an input signal to PCM. The PCM uses this
signal for controlling operation of overdrive solenoid on the valve
body.
When overdrive switch is in the OFF position, OD light on
instrument panel will be illuminated and transmission will not upshift
into 4th gear for overdrive operation. When OD switch is in the ON
position, OD light on instrument panel will not be illuminated and
transmission will upshift into 4th gear for overdrive operation.
If OD switch is in the ON position, the TCC will lock-up when
transmission is in 4th gear with vehicle speed greater than 45 MPH. If
overdrive switch is in the OFF position, the TCC will lock-up when
transmission is in 3rd gear with vehicle speed greater than 35 MPH at
light throttle application.
THROTTLE POSITION (TP) SENSOR
The TP sensor delivers an input signal to the PCM to indicate
throttle position. The PCM uses this input signal for controlling TCC
operation, governor pressure and upshift into 4th gear for overdrive
operation.
TRANSMISSION FLUID TEMPERATURE SENSOR
NOTE: Transmission fluid temperature sensor may also be referred to
as transmission fluid temperature thermistor or transmission
fluid temperature sender.
Transmission fluid temperature sensor delivers an input
signal to the PCM to indicate transmission fluid temperature. The PCM
uses this input signal for controlling the TCC, overdrive operation
and governor pressure. Transmission fluid temperature sensor is
located on the valve body and is integral with governor pressure
sensor. See Fig. 1.
OUTPUT SHAFT SPEED SENSOR
NOTE: Output shaft speed sensor may also be referred to as
transmission shaft speed sensor or shaft speed sensor.
Output shaft speed sensor is located on overdrive unit
attached to rear of transmission. Output shaft speed sensor is mounted
above the lugs on park gear in the overdrive unit. Speed sensor input
signals are generated when lugs on park gear rotate past face of
sensor. Input signals are delivered to PCM. The PCM uses this input
signal for controlling transmission operation. The Vehicle Speed
Sensor (VSS) also serves as a back-up to the output shaft speed
sensor. The VSS signal is also an input to the PCM.
TROUBLE SHOOTING
* PLEASE READ THIS FIRST *
NOTE: For symptom trouble shooting, see appropriate AUTOMATIC
TRANSMISSION OVERHAUL article.
PRELIMINARY INSPECTION
Visually inspect all electrical wiring, looking for chafed,