Upshift Indicator - M/T: Description and Operation

An upshift indicator lamp is standard equipment on all instrument clusters, but is only functional on vehicles equipped with a manual transmission. The upshift indicator lamp is located near the upper edge of the instrument cluster overlay, in the upper right quadrant of the cluster. The upshift indicator lamp consists of an upward pointed arrow icon that is a stenciled cutout in the opaque layer of the instrument cluster overlay. The dark outer layer of the cluster overlay prevents the icon from being clearly visible when the lamp is not illuminated. However, an amber lens behind the cutout in the opaque layer of the cluster overlay causes the icon to appear in amber through the translucent layer of the overlay when it is illuminated from behind by a replaceable incandescent bulb and bulb holder unit located on the instrument cluster electronic circuit board. When the exterior lighting is turned ON, the illumination intensity of the upshift indicator lamp is controlled by the panel lamps dimmer rheostat of the headlamp switch. The upshift indicator lamp is serviced as a unit with the instrument cluster.

The upshift indicator lamp gives an indication to the vehicle operator when the transmission should be shifted to the next highest gear in order to achieve the best fuel economy. This lamp is controlled by the instrument cluster circuit board based upon the cluster programming and electronic messages received by the cluster from the Powertrain Control Module (PCM) over the Chrysler Collision Detection (CCD) data bus. The upshift indicator lamp bulb receives battery current on the instrument cluster electronic circuit board through the fused ignition switch output (st-run) circuit whenever the ignition switch is in the ON or Start positions; therefore, the lamp will always be OFF when the ignition switch is in any position except ON or Start. The lamp bulb only illuminates when it is switched to ground by the instrument cluster circuitry. The upshift indicator lamp illumination brightness is also adjustable when the exterior lights are turned ON. The instrument cluster circuitry monitors the headlamp switch panel dimmer rheostat input to the cluster, then adjusts the output voltage to the upshift indicator lamp using the same circuitry and strategies used to control the Vacuum-Fluorescent Display (VFD) dimming level. The instrument cluster will turn ON the upshift indicator lamp for the following reasons:
- Upshift Lamp-ON Message - Each time the cluster receives an upshift lamp-ON message from the PCM indicating the engine speed and load conditions are right for a transmission upshift to occur. The lamp remains illuminated until the cluster receives an upshift lamp-OFF message from the PCM or until the ignition switch is turned to the OFF position, whichever occurs first. The PCM will normally send an upshift 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.
- Actuator Test - Each time the cluster is put through the actuator test, the lamp will be turned ON and OFF in a prescribed sequence to confirm the functionality of the lamp and the cluster circuitry.

The PCM continually monitors the engine speed and load conditions to determine the proper fuel and ignition requirements. The PCM then sends the proper upshift indicator lamp messages to the instrument cluster. If the upshift indicator fails to light during normal vehicle operation, replace the bulb with a known good unit. For further diagnosis of the upshift indicator lamp or the instrument cluster circuitry that controls the lamp, (Refer to INSTRUMENT CLUSTER - DIAGNOSIS AND TESTING). For proper diagnosis of the PCM, the CCD data bus, or the message inputs to the instrument cluster that control the upshift indicator, a DRB III scan tool and the appropriate diagnostic information are required.