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Home >> Chevrolet >> 2021 >> Blazer RS, FWD >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 9 (Engine Controls And Fuel - 2.5L (LCV) - Diagnostic Information And Procedures (1 Of 2)) >> Diagnostic Information and Procedures >> DTC P0068 or P1101 >> Circuit/System Description

Circuit/System Description

WARNING: This page is about a different variant/trim than selected.
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.
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.
    • Low temperature produces a high resistance: 126.8 kohms @ -60°C (-76°F)
    • High temperature produces a low resistance: 62 ohms @ 150°C (302°F)
K20 Engine Control Module The control module contains a microprocessor used to process input data to control outputs.
The control module controls a series of actuators to ensure optimal engine performance. The control module does this by reading values from a variety of sensors, interprets the data and adjusts the engine actuators accordingly.
Q38 Throttle Body The component Q38 contains a contact less 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 K20.

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.

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