GM Service Manual Online
For 1990-2009 cars only

Distribution of Hydraulic Pressure

As the engine turns, the automatic transmission fluid (ATF) pump starts to operate. ATF is drawn through the ATF filter and discharged into the hydraulic circuit. ATF flowing from the ATF pump becomes line pressure that is regulated by the regulator valve. Torque converter pressure, from the regulator valve, enters the torque converter through the lock-up shift valve and is discharged from the torque converter. The torque converter check valve prevents torque converter pressure from rising.

The powertrain control module (PCM) controls the shift solenoid valves ON and OFF. The shift solenoid valves control shift solenoid pressure to the shift valves. Applying shift solenoid pressure to the shift valves moves the position of the shift valve, and switches the port of hydraulic pressure. The PCM also controls the automatic transmission clutch pressure control (AT CPC) solenoid valves A and B.

The AT CPC solenoid valves A and B regulate the AT CPC solenoid pressure and apply the AT CPC solenoid pressure to CPC valves A and B. When shifting between upper gear and lower gear, the clutch is engaged by pressure from the CPC pressure mode.

The PCM controls one of the shift solenoid (SS) valves to move the position of the shift valve. This movement switches the port of the CPC and line pressure. Line pressure is then applied to the clutch, and the CPC pressure is intercepted.

When shifting is completed, the clutch is engaged with line pressure.

Hydraulic Pressure at the Ports

Port No.

Type of Pressure

Port No.

Type of Pressure

Port No.

Type of Pressure

1

Line

5N

CPC A or Line

56

LS A

2

Line

5D

CPC B or Line

57

LS B

3

Line

5G

CPC B or Line

58

LS C

3'

Reverse CPC or Line

5K

CPC B or Line

90

Torque Converter

3"

Reverse CPC or Line

6

Modulate

90'

Torque Converter

4

Line

SA

SH A

91

Torque Converter

4'

Line

SB

SH B

91'

Torque Converter

4"

Line

SC

SH C

92

Torque Converter

4A

CPC A

LA

LC A

93

ATF cooler

4B

CPC B

9

Line

94

Torque Converter

4C

CPC C

10

1st Clutch

95

Lubrication

5B

CPC A

15

1st Hold Clutch

95'

Lubrication

5C

CPC B

20

2nd Clutch

96

Torque Converter

5H

CPC B

25

Line

97

Torque Converter

5J

CPC B

30

3rd Clutch

99

Suction

5A

CPC A or Line

40

4th Clutch

X

Drain

5E

CPC A or Line

50

5th Clutch

HX

High Position Drain

5F

CPC A or Line

51

5th Clutch

hX

High Position drain

5M

CPC A or Line

55

CPC C or Line

AX

Air Drain

    • CPC: Clutch Pressure Control Pressure
    • SH: Shift Solenoid Pressure
    • LS A: AT CPC Solenoid A Pressure
    • LS B: AT CPC Solenoid B Pressure
    • LS C: AT CPC Solenoid C Pressure
    • LC: Torque Converter Clutch Solenoid Pressure

D or I Position: Driving in 1st gear

The PCM turns SS valve A and C ON, and SS valve B stays ON. SH A pressure (SA) in the right side of shift valve A and E is released, and shift valve A and E are moved to the right side. SH C pressure (SC) in the right side of shift valve C is released, and modulator pressure (6) is applied to the left side of shift valve C. Shift valve C is moved to the right side. These valve movements release CPC C pressure (4C) from the back of the 1st accumulator and the 3rd clutch, and the 1st clutch is engaged securely.

When used, ''left'' or ''right'' indicates direction on the hydraulic circuit.

Drive or Intermediate - First Gear


Object Number: 1254708  Size: FS