General System Description

Electronic Transmission Control System:

General Description

The electronic transmission control system has a control module that monitors a number of engine and vehicle functions for the data needed to control the following operations:

^ [1][2]Torque converter clutch engagement.

^ Upshift pattern.

^ Downshift pattern.

^ Line pressure for smoother shifts.

The module used is called a Powertrain Control Module (PCM). The PCM controls a number of engine functions such as: fuel control, exhaust gas recirculation, and ignition timing, in addition to the above transmission functions. For further information on these systems, refer to "Computers and Control Systems". The same module is used with diesel engines. The diagnosis in this section requires the availability of a scan tool to interface with the Powertrain Control Module (PCM).

HYDRA-MATIC 4L60E Transmission:

TRANSMISSION GENERAL DESCRIPTION

The HYDRA-MATIC 4L60-E is a fully automatic rear wheel drive electronically controlled transmission. It provides four forward ranges including overdrive, and reverse. Shift points are controlled by the PCM via two shift solenoids. Oil pressure is supplied by a vane type oil pump, and regulated by the PCM with a transmission pressure control solenoid (force motor). Shift schedules and TCC apply rates are also controlled by the PCM and are influenced by transmission temperature.

The transmission can be operated in any one of the following seven modes:

P - Park position prevents the vehicle from rolling either forward or backward. (For safety reasons the parking brake should be used 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 this position may be selected if the engine must be restarted with the vehicle moving.

OD- Overdrive is used for all normal driving conditions. It provides four gear ratios plus converter clutch operation. Downshifts are available for safe passing by depressing the accelerator.

D - Drive position is used for city traffic and hilly terrain. It provides three gear ranges. Again, downshifts are available by depressing the accelerator.

2 - Manual second is used to provide acceleration, engine braking, or greater traction from a stop. When manual second is chosen, the vehicle will start out and remain in second gear. This range may be selected at any vehicle speed.

1 - Manual Lo is used to provide maximum engine braking. This range may also be selected at any vehicle speed.

Range Reference Chart:

TRANSMISSION COMPONENT AND SYSTEM DESCRIPTIONS

The mechanical components of this unit are:

- Torque converter with converter clutch (TCC)

- Vane type oil pump

- Five multiple disc clutches

- 2-4 band assembly

- Two planetary gear sets

- One sprag clutch

- One roller clutch

- Control valve assembly

The electrical components of this unit are:

- Powertrain Control Module PCM Located remotely from transmission inside passenger compartment.

- Two shift solenoids

- 3-2 downshift solenoid

- Transmission pressure control solenoid (force motor)

- Torque converter clutch solenoid and wiring harness assembly

- Transmission fluid temperature sensor

- Fluid pressure switch assembly

- Vehicle speed sensor (2WD only)

Refer to Fig. 2 for component locations. Refer to Range Reference Chart (Fig. 3) for component operation in all seven modes of transmission operation.

Transmission Adapt Function

The HYDRA-MATIC 4L6O-E uses a line pressure control system which has the ability to adapt the system's line pressure to compensate for normal wear of clutch fib& plates, seals, springs, etc. This "learning" feature is similar to what is used for fuel control (integrator/block learn).

The HYDRA-MATIC 4L60-E transmission only uses the adapt function for the 1-2 upshift. The PCM monitors engine speed to determine if the shift is occurring too fast (harsh) or too slow (soft) and adjusts the pressure control solenoid to maintain the correct shift feel. The line pressure can adapt to values ranging from 5 psi below, to 10 psi above normal line pressure.