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Vacuum pump

Vacuum pump

To further increase the braking power on the Saab 9-3 Turbo with automatic transmission and the Saab 9-3 Diesel, these cars are fitted with an extra vacuum pump. This extra pump supplies the brake servo with vacuum when the engine is not capable of doing so sufficiently.

The turbo engine with automatic transmission has an electric or mechanical vacuum pump.

The diesel engine has a mechanical vacuum pump.

Electric pump


The pump is located under the left-hand front wing and is connected via a non-return valve to the brake servo. The pump is supplied with current via a relay in the relay box in the engine bay. The relay is controlled from pin 52 of the engine control module, which is grounded to start the pump. 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.

The conditions for control module activation of the output to start the pump 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 will be 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 by means of the diagnostics instrument.

Mechanical pump


The pump is a ring pump which is mounted on the cylinder head and driven by the camshaft. As the pump is connected to the camshaft, the pump speed is half the engine speed, and a vacuum is constantly produced for the brake system.