RAM 2500 Truck 2WD L6-5.9L DSL Turbo VIN 6 (1998)
Shift Indicator: Description and Operation
SYSTEM OPERATION
Upshift Indicator Lamp
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 turned on by the instrument cluster circuitry for about three seconds
when the ignition switch is turned to the On position as a bulb test. After the bulb test, the lamp is controlled by the instrument cluster circuitry
based upon messages 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 messages to the instrument cluster on the CCD data bus to turn the lamp on or off. The PCM
will send lamp-off messages 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.
