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Vacuum pump

Vacuum pump

To further increase the braking power on the Saab 9-3 Diesel and Saab 9-3 Turbo with automatic transmission, these cars have been equipped with an extra vacuum pump. The pump supplies the brake servo with a vacuum when the engine is not capable of doing it sufficiently.

The turbo engine with automatic transmission has an electric vacuum pump. The pump is located under the left-hand front wing and is connected via a non-return valve to the brake servo. The connection cable has three diodes connected in series to ensure that the pump is fed with the correct voltage, and that the correct pump speed is attained.

Diesel engines have a pump that is driven directly from the engine camshaft and therefore supplies the brake system with a continuous vacuum.

Electric pump


The pump is supplied with current by a relay in the relay box under the bonnet. The relay is controlled from engine control module pin 52 which is grounded to start the pump.

The conditions for control module activation of the output are as follows:


• The engine has started

• The pressure in the intake manifold exceeds 58 kPa

• The accelerator is released

• The brake pedal is depressed


When the above conditions are fulfilled, the pump is activated for 3 seconds.

For a description of engine control module operation, see . System overview Saab Trionic T5 or System overview Saab Trionic T5 OBDII .

Diagnosis

The relay can be activated with the diagnostics instrument.

Mechanical pump

The pump of ring type is mounted on the cylinder head and driven by the camshaft. Through connection to the camshaft, the speed of the pump is half that of the engine and vacuum for the brake system is produced continuously.