Driving Modes
Detroit transmissions have twelve forward gears and up to four reverse gears that can be shifted automatically or manually. Shifting and clutch actuation are computer controlled, and there is no clutch pedal needed to operate the vehicle. Automatic shifts are selected for fuel economy or engine power. Manual shifts can be requested with the shift control and the transmission ECU grants them when conditions permit. In all cases, shifts depend on the following factors: engine speed, accelerator pedal position, service brake usage, engine brake operation, vehicle load status, and road conditions.
Note: To avoid potential engine stall risk or unexpected shifting, use the interaxle differential lock when the vehicle is operated in slippery conditions. See Chapter 16 for information about the interaxle differential lock.
There are three driving modes: Manual, Automatic Economy, and Automatic Performance. To activate the manual drive mode, press and hold the mode switch briefly. Press the switch quickly to activate the automatic drive mode or change between modes. See Fig..
In Automatic Economy mode, gear shifts are designed for saving fuel. In Automatic Performance mode, gear shifts are designed for higher performance and are made at higher engine speeds. In manual mode, gear shifts are requested manually.
See Table for a description of control functionality.
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Rotate for drive (D), neutral (N), or reverse (R).
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Short press for automatic mode or switch between available modes.
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Long press for manual mode.
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Pull for upshift (+) request.
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Push for downshift (-) request.
Fig. 1, Automated/Automatic Transmission Shift Control
Note: In Automatic Performance mode, the transmission will automatically change to Automatic Economy mode if it hasn't received a request for more power in several minutes, unless current road conditions require higher engine performance.