Cherokee 4WD L6-4.0L VIN S (1998)
Shift Indicator: Description and Operation
SYSTEM OPERATION
Vehicles equipped with a manual transmission have an upshift indicator lamp. The upshift indicator lamp gives an indication when the driver
should shift to the next highest gear for the best fuel economy. The lamp is controlled by the instrument cluster circuitry based upon a message
received from the Powertrain Control Module (PCM) on the Chrysler Collision Detection (CCD) data bus.
The PCM uses inputs from many sensors and its internal programming to decide whether the engine speed and load conditions are correct for a
transmission upshift. The PCM then sends the proper message to the instrument cluster on the CCD data bus to turn the lamp on or off. The PCM
will send a lamp-off message three to five seconds after a lamp-on message, if an upshift is not performed. The lamp will then remain off until the
vehicle stops accelerating and is brought back into the range of lamp operation, or until the transmission is shifted into another gear. If the
instrument cluster circuitry receives no lamp-off messages from the PCM following a lamp-on message, the cluster will keep the lamp turned on
until the ignition switch is turned to the Off position.
