Line pressure solenoid, STH

WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2006 Volvo S80, 2005 Volvo S80, 2004 Volvo S80, 2003 Volvo S80, and 2002 Volvo S80. However, it is still accessible from the selected car via links, so may be relevant.

Fig 1: Line Pressure Solenoid, STH

Courtesy of VOLVO CARS OF NORTH AMERICA.

The line pressure solenoid, STH, is positioned in the valve housing, which is behind the side cover for the transmission. The line pressure solenoid consists of an electrical coil which controls a hydraulic valve. The solenoid is controlled by pulse width modulation (PWM) voltage and is grounded via the transmission control module (TCM). The function of the solenoid is linear. The hydraulic valve is controlled by the varied current which is the result of the pulse conditions. During high pulse conditions, (at high current (approximately 1A)) the line pressure is low. During low pulse conditions (at low currents) the line pressure is high. In the event of an open-circuit, the line pressure reaches maximum which will result in harsh gear shifting. This can also result in a whining noise from the transmission pump. The hydraulic valve is then completely open.

There are diagnostics for the solenoid. There is a diagnostic for the electrical function of the solenoid. There is also a diagnostic for the hydraulic circuit, but not for the hydraulic function of the solenoid. The hydraulic tests can be carried out using a mechanical pressure gauge. The idle and stop pressure can be checked.