LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Volvo >> 2009 >> XC70 Base >> Repair and Diagnosis >> Engine Performance >> Engine Control Systems >> Electrical Modules And Components - Design And Function - 5 Of 5 >> Transmission >> Design And Function >> The Hydraulic System
April 5, 2026: LEMON Manuals is launched! Read the announcement.

The Hydraulic System

Fig 1: Identifying Hydraulic System
GLL156319Courtesy of VOLVO CARS CORPORATION
Number  Designation  Number  Designation 
1 Transmission control module (TCM) 5 Oil cooler
2 Torque converter 6 Oil pump
3 Valves and solenoids 7 Planetary train
4 Clutches and brakes 8 Oil sump

The transmission's hydraulic system consists of oil pump, torque converter, hydraulic control system and oil cooler.

The solenoids, which control the hydraulic valves, are located in the transmission's control system, which are mounted on the front edge of the transmission. The solenoids are activated by the Transmission control module (TCM).

The oil pump supplies the hydraulics with oil and supplies the other components of the transmission with oil for lubrication and cooling. Excess oil is routed back to the oil sump.

CAUTION:

The transmission oil differs from conventional ATF oil properties. Always use transmission oil that is specified for this transmission. Otherwise the function of the transmission will be damaged.

The oil level is checked though a level pipe (transmission does not have conventional oil dipstick).

Fig 2: Identifying Transmission Control Module (TCM), Solenoids And Sensors
GLL156320Courtesy of VOLVO CARS CORPORATION
S1 = Solenoid, S1 SLU = Lock-up solenoid, SLU
S2 = Solenoid, S2 C1 = Clutch, C1
SLC1 = Line pressure solenoid, SLC1 C2 = Clutch, C2
SLC2 = Line pressure solenoid, SLC2 C3 = Clutch, C3
SLC3 = Line pressure solenoid, SLC3 B1 = Brake, B1
SLB1 = Line pressure solenoid, SLB1 B2 = Brake, B2
SLT = Line pressure solenoid, SLT LU = Lock-up

Shifting occurs by the oil pump building up hydraulic pressure. The hydraulic valves, which are controlled by their respective solenoids, send the hydraulic pressure to the relevant clutch, brake or lock-up depending on which signals come from the Transmission control module (TCM).

Hydraulic pressure chamber 

Fig 3: Identifying Hydraulic Pressure Chambers
GLL156804Courtesy of VOLVO CARS CORPORATION

A = Piston's hydraulic pressure chamber

B = Counter acting hydraulic pressure chamber

When the rotation of the clutch increases, the centrifugal force affects the oil inside the clutch. The hydraulic pressure increases and the clutch engages. The centrifugal force means that a difference occurs in the rotation between the input and output shafts, which can mean a shift judder. To solve this, there is an extra pressure chamber opposite the pistons hydraulic pressure chamber. This extra pressure chamber means that the centrifugal force also works in the opposite direction and therefore affects the pressure from the pistons hydraulic pressure chamber. In addition, the clutch does not engage too soon.