Boost Pressure Control

The Saab Trionic system regulates boost pressure by controlling a solenoid valve which is connected to the turbo wastegate. Actual boost pressure is ascertained by the pressure sensor.
Target boost pressure is calculated by the engine control module, mainly on the basis of the following information:
^ engine speed
^ throttle position
^ gear currently engaged
^ knocking, if any





Boost pressure control takes place by means of a 2-coil, 3-way solenoid valve which is connected by hoses to the turbo unit wastegate, compressor outlet and compressor inlet.

The solenoid valve is supplied with power (+54 circuit) via fuse 5 and controlled from pins 26 and 2 of the control module. The control voltage is a PWM signal with a frequency of 90 Hz below 2500 rpm and 70 Hz above 2500 rpm. The change in frequency at 2500 rpm is to avoid resonance in the air hoses.

The ECM adjusts the boost pressure by alternately grounding pins 26 and 2. As a result of grounding pin 2 a longer time than pin 26 the boost pressure is reduced, and conversely the boost pressure is increased by grounding pin 26 longer than pin 2.

The control module determines boost pressure on the basis of throttle position and engine speed. The control module obtains the current boost pressure from the manifold absolute pressure sensor. Boost pressure is
reduced slightly in 1st gear. The control module calculates the gear position by comparing the speed of the car with the engine speed.
If the ECM has been de-energized, a number of full throttle accelerations will be needed to obtain a correct build-up of boost pressure.





If knocking occurs, despite retarding the ignition and making the fuel/air mixture richer, the boost pressure is also reduced.
If there is a break in any of the leads to the solenoid valve, basic boost pressure will be obtained.
In the event of a break in any of the hoses or a fault in the solenoid valve, excessively high boost pressure may be obtained. The control module will then shut off fuel injection at about 0.65-1.35 bar, depending on the engine version.

Cars With Automatic Transmission
When the selector lever is moved to a position other than P or N, battery positive voltage (B+) will be applied to pin 14 of the control module, which will be programmed for automatic transmission. Cars with automatic transmission have reduced boost pressure.

Brake Light Switch
When the brake pedal is depressed, current (B+) is supplied to the electronic control module on pin 15 and maximal boost pressure will then be the basic boost pressure.

Reverse
Basic boost pressure will be obtained when reverse gear is engaged. This will take place when battery positive voltage (B+) from the selector lever or reversing light switch is applied to pin 13 of the control module.

Cruise Control
When Cruise Control is activated, pin 36 of the ECM is grounded, making a reduction in boost pressure possible. This does not take place in the Trionic system on the M96 Saab 9000.

Speed Limitation
Vehicle speed on cars equipped with a boost pressure control valve is limited to 149 mph (240 km/h) through boost pressure reduction.