WHAT IS BOOST PRESSURE SENSOR (BPS)?

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WHAT IS BOOST PRESSURE SENSOR (BPS)?​

Boost pressure sensors are used in turbocharged engines to provide air pressure information and air and fuel ratios in order to regulate engine performance. As a complex piece of technology, a boost pressure sensor has been an impressive addition to engine technology. Boost pressure sensors control the boost level produced in the intake manifold of a turbocharged or supercharged engine. They affect the air pressure delivered to the pneumatic and mechanical wastegate actuator.

Principle of operation of the BPS

The boost pressure sensor measures the absolute pressure before the throttle valve. The engine control unit uses its signal to calculate a correction value for the boost pressure. By detecting the amount of boost and air density in the car's intake manifold, the car's electronic control unit or ECU can determine how much fuel is needed in the car's combustion chamber so that the air-fuel mixture is at its best. Proper air-fuel mixture is critical to engines since this translates to better and more efficient power production. This not only makes the engine more powerful, but also makes the engine run effectively, maximizing every drop of fuel.

When the manifold pressure is low (high vacuum) sensor voltage output is 0.25-1.8V at the ECM. When the intake manifold pressure is high due to turbo boost, sensor voltage output is 2.0-4.7V. Pressure range is between 10kPa and 350kPa. The sensor receives a 5V reference from the ECM. Sensor ground is also provides by the ECM. The ECM uses boost pressure combined with intake air temerature to determine the volume of air entering the engine.

How to verify functionality of the BPS?

Testing the supply voltage

• Disconnect the plug from the sensor.
• Turn on the ignition.
• Set the multimeter to “DC voltage”.
• Measure the supply voltage between pin C (3) and earth A (1). It should be approximately 5V.
• If this value is not reached, the fault in the voltage supply must be located.

Testing the output signal

• Remove the pressure sensor from the intake manifold.
• Connect the vacuum hand pump to the pressure sensor.
• Turn on the ignition.
• Set the multimeter to “DC voltage”.
• Set the lower absolute pressure value P-low.
• Test the lower output signal U-low between pin B (2) and earth A (1).
• Set the upper absolute pressure value P-high.
• Test the upper output signal U-high between pin B (2) and earth A (1).

Fast verification of the BPS using an oscilloscope

• Restore all connections to the BPS as during normal engine work.
• Attach the ground lead of the oscilloscope to the chassis ground.
• Connect the active oscilloscope test lead to the signal terminal of the BPS (usually in the middle).
• Start the engine and leave it idling.
• Sharply press the throttle and then immediately release it. Note that voltage will not rise up to its maximum when the car is not running. This is normal due to the low engine load.
• You should watch DC output signal varying from 1.0V to 3.0V, which will change simultaneously with the throttle position.

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Possible failures in the BPS:

• Chaotic output signal
• Chaotic output signal is, when the voltage signal changes randomly, drops to zero and disappears.
• This usually happens when an inefficient BPS is present. In this case the sensor must be replaced.
• Missing of signal voltage
• Check whether the supply voltage is applied (+5.0V).
• Check the grounding for problems.
• If the supply voltage and the grounding are correct, check the signal wire between the BPS and the onboard controller.
• If the supply voltage and/or grounding are not correct, check the integrity of the wires between the sensor and the ECU.
• If all wires of the sensor are correct, check all connections for the reference voltage and ground of the onboard controller.
• If they are correct under suspicion falls the controller.
• The BPS power supply or signal is equal to the car battery voltage.
• Check for a short circuit to the positive terminal of the car battery.

Other checks:

• Check for excessive fuel in the vacuum hose or trap.
• Check the vacuum hose for leaks and/or other damages.
• Check for mechanical damaged parts of the engine, ignition system or in the fuel system, causing low vacuum.