I. Installation Location and Function
1. Intake manifold absolute pressure and temperature sensor
This combined sensor is bolted inside the plastic intake manifold. The sensor measures the pressure and temperature within the intake manifold.
Signal usage: The engine control unit calculates the intake air quality based on the signal and engine speed.
Impact of signal loss: When a signal is lost, the throttle position and intake air temperature sensor temperatures are used as substitute signals.
2. Pressure and temperature sensors (rear)
This combined sensor is bolted to the intake manifold connector behind the turbocharger or throttle body. The sensor measures the intake pressure and temperature in this area.
Signal usage: The control unit adjusts the turbocharger pressure based on the signal. The intake air temperature sensor signal is also used to prevent components from overheating. Turbocharger power is limited when the temperature exceeds 130°C.
Impact of signal loss: When the combined sensor malfunctions, turbocharger pressure regulation cannot continue. Turbocharger operation modes are no longer permitted, and the turbocharger can only operate under controlled conditions. Engine power decreases significantly in the low-speed range.
3. Pressure and temperature sensors (front)
This combined sensor is screwed into the boost air pipe just in front of the throttle control unit. The sensor measures the pressure and temperature in this area.
Signal usage: The engine control unit adjusts the boost pressure of the turbocharger through the boost pressure limiting solenoid valve based on the boost pressure sensor signal.
The corrected value for the boost pressure is calculated using the intake air temperature sensor signal. The effect of temperature on the density of the boost air is taken into account.
Impact of signal loss: When sensors malfunction, the turbocharger can only operate under controlled conditions. Further sensor failures may also cause the compressor to shut down.
II. Structural Principles and Testing
1. Intake pressure sensor
(1) Structural principle
The structure of a semiconductor piezoresistive intake pressure sensor is shown in the figure below. It is made using the piezoresistive effect of semiconductors and mainly consists of a silicon wafer, an absolute vacuum pump, a circuit converter (IC amplifier), a base, a vacuum tube, and electrode leads.
Semiconductor piezoresistive intake pressure sensors have good linearity and advantages such as small size, high accuracy, and good response characteristics. Therefore, they are widely used in modern automotive engine electronic control systems.
The working principle of the semiconductor piezoresistive intake pressure sensor is shown in the figure below. One side of the silicon diaphragm passes through the vacuum chamber, while the other side is subjected to the pressure of the gas from the intake manifold. Under the action of this gas pressure, the silicon diaphragm will deform, and the greater the pressure, the greater the deformation. The resistance of the strain resistor on the diaphragm will change under this compressive stress, which will break the balance of the strain resistors of the silicon diaphragm connected in the Wheatstone bridge manner on the sensor. When a certain voltage or current is input to the input terminal of the bridge, a corresponding change in signal voltage or signal current can be obtained at the output terminal of the bridge. Because this signal is relatively weak, a hybrid integrated circuit is used to amplify it before inputting it to the ECU.
(2) Typical vehicle series application
The circuit diagram of the absolute pressure sensor in the new Cruze series is shown below. The manifold absolute pressure sensor has a 5-volt reference voltage circuit, a low-level reference voltage circuit, and a signal circuit. The engine control module (ECU) provides a 5-volt reference voltage to the manifold absolute pressure sensor and grounds the low-level reference voltage circuit. The manifold absolute pressure sensor provides a voltage signal related to changes in intake manifold pressure to the ECU via the signal circuit.
(3) Detection
Routine testing (circuit diagram as shown above)
① Visual inspection: Inspect the sensor’s vacuum tube, connectors, and wiring for any looseness, damage, or other abnormalities.
② Check the sensor power supply voltage: Turn on the ignition switch (ON) and use a DC voltmeter to measure the voltage between terminals 1 and 2 of the sensor. It should be 5V. If the voltage is abnormal, check the wiring between the sensor and the engine control module K20. If the wiring is normal, check the ECU's power supply and ground wiring. If the wiring is still normal, replace the engine control module K20.
③ Check the sensor signal voltage: Turn on the ignition switch (ON) and use a DC voltmeter to measure the voltage between terminals 3 and 2 of the sensor; it should be around 4V. Start the engine and measure the voltage between terminals 3 and 2 while the engine is idling; it should be 1-1.5V. Gradually increase the throttle opening to raise the engine speed, and simultaneously measure the voltage between terminals B and A of the sensor; it should gradually increase to 5V.
If the measured sensor signal voltage is abnormal, the sensor needs to be replaced.
(4) Detection of absolute pressure sensor in Cruze series
The Cruze series has three fault codes for its absolute pressure sensor circuit: "DTCP0106: Manifold Absolute Pressure (MAP) Sensor Performance Issues", "DTCP0107: Manifold Absolute Pressure (MAP) Sensor Circuit Voltage Too Low", and "DTCP0108: Manifold Absolute Pressure (MAP) Sensor Circuit Voltage Too High". This article uses these codes as examples to illustrate how to troubleshoot absolute pressure sensor faults. Refer to the circuit diagram above for the Cruze absolute pressure sensor, and the terminal block diagram below.
2. Intake air temperature sensor
The structure of the intake air temperature sensor is shown in the figure below. It mainly consists of an insulating sleeve, a plastic shell, a waterproof socket, a copper washer, and a thermistor.
The intake air temperature sensor uses a thermistor with a negative temperature coefficient as the detection element. To accurately measure the intake air temperature, it is usually protected by a plastic housing to prevent the temperature of the installation part from affecting the working accuracy of the sensor.
(1) Typical vehicle series circuit connection
The diagram below shows the circuit connection of the intake air temperature sensor in the new Cruze's turbocharged engine. The intake air temperature sensor is integrated with the turbocharger sensor and installed in the intake manifold behind the turbocharger. The engine control unit (ECU) provides a 5V reference voltage to sensor #3, while sensor #1 is grounded internally through the ECU.
(2) Detection
A malfunctioning intake air temperature sensor can cause the air-fuel mixture to be too rich or too lean, resulting in poor combustion and unstable operation. In this case, the intake air temperature sensor should be checked.
The detection method for the intake air temperature sensor is as follows:
①Single-unit detection
Turn off the ignition switch, disconnect the intake air temperature sensor wiring harness connector, and remove the intake air temperature sensor.
The intake air temperature sensor can be cooled using refrigerant or compressed air, or it can be heated by immersing it in water.
When measuring the resistance between the two terminals of the sensor using a multimeter in resistance mode, the resistance value should change with temperature in a manner consistent with the characteristic curve shown in the figure below.
② Online detection method
Disconnect the sensor connector, turn on the ignition switch, and measure the voltage between terminal #3 on the connector and ground. It should be 5V. If there is no voltage, check the voltage between terminal #34 on the ECU connector and ground. If the voltage here is 5V, it indicates an open circuit between the ECU and the sensor; if there is no 5V, the ECU is faulty.
Reinsert the plug, start the engine, and measure the voltage between sensor #3 terminal and ground at different temperatures. It should vary between 0.5 and 4V (slight differences may occur depending on the vehicle model, but the general pattern of variation is the same).
If the measured value does not match the specified value, it indicates that the intake air temperature sensor is faulty or damaged and should be replaced with a new one.
