The working principles and testing standards of various sensors.
1. Liquid level and temperature sensor
Temperature: Installed on the urea tank, it can detect the temperature of the urea solution, heat the urea solution with engine hot water, and monitor the liquid level. It sends alarm signals to the ECU when the tank is full, at zero level, or empty.
Bosch sensor series characteristics
Weichai liquid level and temperature sensor
Liquid level: The Xichai and Weichai Bosch pumps are installed inside the urea pump to detect the urea pressure level.
Bosch sensor series characteristics
Weichai liquid level and temperature sensor
2. Urea pressure sensor
Bosch sensor series characteristics
Weichai engine urea pressure sensor
3. NOx sensor
Its function is to detect the emission level of the toxic gas NOx in exhaust gas. There are two types of NOx sensors: one is BOSCH, and the other is Cummins.
Damage will result in:
1. Not burning urea 2. Cannot refuel 3. Insufficient power 4. CAN bus communication failed
4. Crankshaft position sensor or camshaft position sensor
Structure: Electromagnetic and Hall effect types
Functions: The speed sensor collects diesel engine speed signals so that the ECU can calculate the cyclic fuel supply quantity, and can also provide crankshaft position signals so that the ECU can make accurate control of fuel injection timing; the auxiliary speed sensor is used as a speed signal to calculate the crankshaft angle and perform cylinder identification.
Installation location: flywheel housing, behind the fan. The gap between the sensor and the signal disk should be 0.5–1.5 mm.
Synchronization status: The synchronization signal is 48 for Bosch Euro III and 30 for Bosch EDC17 Euro IV system.
Operating voltage: Electromagnetic type has no operating voltage, and its resistance is approximately 860 ohms. Hall effect type has an operating voltage with three wires: 5V, signal, and ground.
Fault symptoms: a) Difficult to start b) White smoke c) Insufficient power d) ECU repair fault report: pressure relief valve open (usually caused by signal disc jumping or improper signal disc replacement by mechanic) e) Cannot start. When your vehicle reports a crankshaft position sensor fault or camshaft position sensor fault, you can swap the two sensors because their sensor structures and principles are exactly the same.
For example, if the crankshaft position sensor is reported as faulty, and the fault persists even after swapping the sensor, it indicates a problem with the wiring harness from the crankshaft position sensor to the ECU. If the fault is reported as faulty with the camshaft position sensor, it means the original crankshaft position sensor is faulty, and replacing the sensor will solve the problem.
5. Water temperature sensor
Structure: A thermistor with a negative temperature coefficient, its operating range is 40-130℃.
Function: It indicates the engine temperature by measuring the temperature of the coolant. The coolant temperature signal can be used for cold starts and fan control, etc. It is mainly used to measure the engine cooling temperature, thereby further precisely controlling the fuel injection quantity.
Installation location: The coolant temperature sensor is installed in the coolant circulation loop.
Operating voltage: One wire is a 5V signal voltage, and the other is a ground wire.
Abnormal water temperature sensor signals can cause the following problems with engine operation:
1. The generated low temperature signal may cause the ECU to think that it is in a cold start enrichment condition, increase fuel injection, resulting in an overly rich air-fuel mixture, incomplete combustion of the engine, and reduced power.
2. The generated high temperature signal can make the ECU think that the engine is hot and limit fuel to reduce the engine speed.
3. The car will shut off or limit its speed to 1500 RPM if the temperature exceeds 100 degrees Celsius.
4. Cylinder failure test, acceleration test, and high pressure test all require a temperature of 75 degrees Celsius or higher.
5. The electric fan needs to operate at a temperature between 85 and 93 degrees Celsius.
6. Intake preheating requires a water temperature signal. The aftertreatment system injection and EGR operation also require a temperature above 70 degrees Celsius.
6. Pressure boosting sensor
Structure: Semiconductor piezoresistive pressure sensor.
Functions: Calculates air volume using a thermistor to control the air-fuel ratio and negative temperature coefficient, thereby further refining fuel injection control. The boost pressure sensor measures the absolute pressure within the intake manifold. Engine intake volume is determined by intake pressure and engine speed. The Bosch LDF6T sensor integrates both a pressure sensor and a temperature sensor.
Installation location: The boost pressure sensor is typically installed after the turbocharger. (Weichai computer version corresponds to boost pressure information.)
Weichai engine boost pressure sensor
This phenomenon is caused by a problem with the boost pressure sensor.
1. Damaged intake pressure leads to insufficient power, white smoke, and black smoke.
2. How to determine insufficient intake air volume: "Look at the data." Generally speaking, the maximum intake air volume for a six-cylinder engine is 1200Hpa (120Kpa) when the engine is empty and accelerating, and approximately 2600Hpa (260Kpa) when climbing hills or driving with a heavy load. The intake pressure sensor is an important basis for the ECU to calculate the amount of fuel injection. Abnormal signals: High voltage signals can cause the ECU to think it is maintaining the air-fuel mixture ratio and increase the amount of fuel injection, resulting in a weak engine and black smoke. When the limit is exceeded, the ECU will suddenly cut off power and fuel supply. Low voltage signals can cause the ECU to reduce the amount of fuel injection, resulting in a weak engine.
7. Rail pressure sensor
Structure: Piezoresistive high-voltage sensor, maximum frequency 1kHz, maximum operating rail voltage: 1600bar
Function: The common rail pressure sensor measures the actual pressure signal in the common rail in real time and feeds it back to the ECU to adjust the fuel pressure. The common rail pressure sensor measures the actual pressure within the common rail of the high-pressure common rail system. It converts the pressure value into a voltage signal for the ECU to achieve closed-loop control of the fuel pressure.
Installation location: Damage to the rail pressure sensor on the common rail can cause excessively high rail pressure, open the pressure relief valve to limit the speed to 1700 rpm, or prevent the vehicle from being manufactured.
8. Accelerator pedal position sensor
The accelerator pedal position sensor converts the accelerator pedal opening into an electronic signal and outputs it to the engine controller.
Structure: Non-contact sensor
Features: The vehicle has two sensors. A linkage rotates together with the accelerator pedal, and the output terminal voltage changes according to the rotation angle of the linkage.
1. Six-wire two-set sensor: The voltage at throttle position 1 is twice that at throttle position 2.
Different car models can use the same 5V power supply and ground wire. If the 5V voltage wire of throttle position 1 is broken, you can run a wire from throttle position 2.
Weichai engine position sensor
2. Five wires for the throttle pedal sensor. Three of these are for the position sensor, plus two for the idle speed switch (Hongyan Jieshi, Hengyang unit pump, Weite unit pump).
9. Fuel water content sensor
The lower part S of the oil-water separator is equipped with a fuel water content sensor. When the water in the fuel reaches the height of the two electrodes of the sensor inside the oil-water separator, the conductivity of water short-circuits the two electrodes, at which point the water level warning light illuminates. If wires 1 and 2 are directly exposed in the fuel and there is water, the two wires will conduct, resulting in insufficient power.
The resistance between pins 1 and 2 is infinite.
The resistance between pins 2 and 3 is 4MΩ.
The resistance between pins 1 and 3 is 1.5–2.5 MO.
Structure: Similar to water temperature, high fuel temperature can cause the engine to stall or limit speed.
Denso systems typically have the S-mount on the return oil line; Bosch systems typically have the S-mount on the filter element (some systems don't have it); Delphi systems have it on the oil pump; and single-pump systems have it on the oil pump. The throttle position 2, remote throttle, and fan speed share a 5V voltage and ground wire; Cummins systems use a dedicated 3-wire wire, and damage to this wire can cause slow refueling, no refueling, and speed limitation.
Function: To detect the presence of oil in the oil pan and provide a warning. No operating voltage.
Principle: Thermistor type, measured when the engine is off. The EECU sends a 200mA current every 15 seconds for 1.75 seconds, causing the metal wire to heat up. The amount of fuel determines the degree of heat dissipation of the metal wire, thus affecting the resistance of the metal wire, thereby determining the oil level.
Different car models are equipped with different features:
1. Howo A7 port definition: 1 is 24 to 28V power supply voltage, 2 is ground, 3 is signal to pin 27 of the computer board, and 4 is signal to pin 3.22 of the CBCU port/dashcam. The signal voltage is approximately 4V.
2. The three wires for the Delong M3000 vehicle speedometer are: 1. Live wire (12/24V), 2. Ground wire, and 3. Signal wire. The signal output connects to the converter and then to the instrument panel (A14).
3. The Tianlong vehicle speed indicator has three wires, all coming from the instrument panel: 1 is the power wire (12V), 2 is the signal wire (around 7.5V when the ignition is on), and 3 is the ground wire. The speed signal goes to the instrument panel, then to the VECU and EECU.
4. Buses typically have four wires: 1 is a live wire (12/24V), 2 is a signal wire to the ECU, 3 is a signal wire to the instrument panel/GPS/driving recorder, and 4 is a ground wire.
5. The J6 three-wire connection goes directly to the instrument panel's live wire, ground wire, and signal wire.
