Driver Controls and Instruments NOTE: The ignition switch must be on for the high beams to work. Allison Automatic Transmission Controls 1 Allison automatic transmission models MD-CR and MD-WR are controlled by an electronic control unit (ECU). The ECU processes information from sensors, pressure switches, and the shift selector to automati- cally control the transmission according to programmed specifications. See Fig. 3.18 . 2 Vehicles with these transmissions have a red do-not- shift light in the lens and bezel assembly. Also, there is a service light in the indicator panel on the shift selec- tor.
With the ignition switch on, both lights come on for a few seconds, then if there is no problem with the transmission system, the lights will go out. Whenever there is a problem with the transmission system, the lights will come on and stay on as long as the problem exists. 10/28/94 f600368a 1. Indicator Panel 2. Mode ID If "service" is displayed in the indicator panel, some fea- tures may not work, but the vehicle can still be driven. If the do-not-shift light illuminates while driving (accompa- nied by eight short beeps from the shift selector), oper- ating limits will be placed on the transmission, such as restricting upshifts and downshifts.
However, the vehicle can still be driven to reach service assistance. In either situation, have the problem repaired as soon as pos- Fig. 3.18, Shift Selector sible. See the Allison Transmission Service Manual for troubleshooting procedures. See Chapter 5 for complete transmission operating instructions. 3.17