Circuit/System Description
| Component | Description |
|---|---|
| B74 Manifold Absolute Pressure Sensor | The sensor is a capacitive pressure transducer. Electronics in the sensor convert pressure into an analog voltage signal. |
| B75C Multifunction Intake Air Sensor | The assembly contains the following components:
|
| K20 Engine Control Module | The control module contains a microprocessor used to process input data to control outputs. |
| Q38 Throttle Body | Throttle Body Assembly |
B74 Manifold Absolute Pressure Sensor
The sensor measures the pressure in the intake manifold between the throttle valve and the intake valves.
When the engine is idling or decelerating, the sensor pressure should be low. When the engine is off or under wide-open throttle conditions the pressure should be the same or close to the barometric pressure.
B75C Multifunction Intake Air Sensor
The assembly has several functions:
The mass air flow sensor is a hot film type sensor that measures the mass of air (not the volume) entering the engine. The signal varies with engine load and is displayed by the scan tool in Hertz (Hz) and grams per second (g/s).
The intake air humidity sensor uses the same signal circuit as the intake air temperature sensor 2. The intake air humidity sensor modulates the pulse width of the signal. The intake air temperature sensor 2 modulates the frequency of the signal. That means the signal is both, PWM and FM modulated.
The barometric pressure sensor generates an analog voltage that is proportional to the ambient air pressure.
The intake air temperature sensor 1 varies its resistance depending on the temperature.
K20 Engine Control Module
The ECM compares the measured mass air flow with the calculated air flow based on throttle position and the calculated air flow based on manifold absolute pressure.This DTC sets when the control module detects an inconsistency between the pressure sensors and cannot identify which sensor failed.
Q38 Throttle Body
The throttle valve is actuated by a bidirectional DC motor. A spring pulls the valve to a rest or default position, in which the valve is almost closed. The throttle actuator motor can push against the force of the spring to open or close the valve. The more current flow through the motor, the more the valve moves.
The component contains a contactless inductive position sensor. A fixed transmitter coil excites a movable rotor, which in turn induces a current in a fixed receiver coil. The current varies with the angle of the rotor. Electronics inside the sensor convert the current into digital data which is transmitted via a serial data circuit to the control module.