GM Service Manual Online
For 1990-2009 cars only

The MU4 is a fully automatic front wheel drive electronically controlled transmission. The PCM controls shift points by means of two shift solenoids. A third solenoid controls the application of the Torque Converter Clutch. A gear driven oil pump supplies the oil pressure. The PCM regulates oil pressure by means of a pressure control solenoid valve.

You can operate the transmission in any one of the following seven modes:

    • P -- Park position prevents the vehicle from rolling either forward or backward. For safety reasons, use the parking brake in addition to the park position.
    • R -- Reverse allows the vehicle to be operated in a rearward direction.
    • N -- Neutral allows the engine to be started and operated while driving the vehicle. If necessary, you may select this position in order to restart the engine with the vehicle moving.
    • Overdrive -- Overdrive is used for all normal driving conditions. Overdrive provides a fourth gear ratio which can be engaged or disengaged manually . Depress the accelerator in order to downshift for safe passing.
    • D -- Drive position is used for city traffic and hilly terrain. Drive provides three gear ranges and drive range prevents the transmission from operating in Overdrive. Depress the accelerator in order to downshift.
    • 2 -- Manual Second provides two gear ratios under most operating conditions. Manual Second provides acceleration and engine braking. Select this range at any vehicle speed, but the transmission will not downshift into Second gear until the vehicle speed drops below approximately 97 km/h (60 mph)
    • 1 -- Manual Lo provides maximum engine braking. You may also select this range at any vehicle speed, but the transmission will not downshift into First gear until the vehicle speed drops below approximately 46 km/h (28 mph).