The oil pressure sensor of an automobile is an important device for detecting the oil pressure of the vehicle engine, and the detected data can help control the normal operation of the engine.
The Structure of the Oil Pressure Sensor
The electronic oil pressure sensor is composed of a thick film pressure sensor chip, a signal processing circuit, a casing, a fixed circuit board device, and two leads (signal line and alarm line). The signal processing circuit is composed of a power supply circuit, sensor compensation circuit, zero adjustment circuit, voltage amplifier circuit, current amplifier circuit, filter circuit, and alarm circuit.
Figure 1 is a structural diagram of the sensor, and Figure 2 is its principle block diagram. The thick-film pressure sensor is a new strain-type pressure sensor that appeared in the 1980s. It is developed by using the piezoresistive effect of thick-film resistors printed and sintered on ceramic elastomers. Four thick film resistors are directly printed and sintered on the ceramic elastic diaphragm and connected to form a Wheatstone bridge through the conduction band. When the measured liquid level pressure acts on the ceramic elastomer, the elastic diaphragm is flexed and deformed. At the same time, the thick film resistor printed on the elastic diaphragm also produces the same amount of strain, of which two of the thick film resistors are under compressive strain and their resistance values decrease; the other two are under tensile strain and their resistance values increase. In this way, the measured pressure value is converted into a bridge output signal, and the magnitude of the signal is proportional to the pressure.
How does an Oil Pressure Sensor Work?
The oil pressure sensor is installed on the main oil passage of the engine. When the engine is running, the pressure measuring device detects the pressure of the oil, converts the pressure signal into an electrical signal, and sends it to the signal processing circuit. After voltage amplification and current amplification, the amplified pressure signal is connected to the oil pressure gauge through the signal line to change the ratio of the currents passing through the 2 coils inside the oil pressure gauge so as to indicate the engine oil pressure. The pressure signal after voltage amplification and current amplification is also compared with the alarm voltage set in the alarm circuit. When the voltage is lower than the alarm voltage, the alarm circuit outputs an alarm signal and lights the alarm light through the alarm line.
The wiring method of the electronic oil pressure sensor is exactly the same as that of the traditional mechanical sensor. It can replace the mechanical pressure sensor and directly connect it with the automobile oil pressure gauge and the low-pressure warning light to indicate the oil pressure of the diesel engine and provide a low-pressure warning signal. Compared with the traditional piezoresistive oil pressure sensor, the electronic automobile oil pressure sensor has the advantages of no mechanical moving parts (ie no contact), high precision, high reliability, long life, etc., and meets the requirements of the development of automobile electronics.
Due to the harsh working environment of the automobile, the requirements for the sensor are very strict. In the design of the electronic automobile oil force sensor, it is not only necessary to select a pressure measuring device with high-temperature resistance, corrosion resistance and high precision, and components with reliable performance and wide operating temperature range but also need to take anti-interference measures in the circuit to improve the reliability of the sensor.
Oil Pressure Sensor Location
According to Repair Pal, the oil pressure sensor is usually located between the oil filter and the oil pan near the bottom right side of the engine. However, the oil pressure sensor, also known as the oil pressure switch or sensor, has different locations depending on the vehicle.
According to Autos, the oil pressure sensor measures the pressure of the engine oil being pumped by the oil pump. A well-working oil pump works 20 to 40 pounds per square inch. If the pressure drops below this range, severe and permanent engine damage can occur. Some vehicles have electric and mechanical oil pressure gauges built into the dashboard, while others have signal lights. The vehicle oil pressure warning system alerts the driver of problems detected by the sensors.
According to AutoZone, the cause of a low oil pressure reading is usually a faulty oil pressure sensor. If the oil pressure in the main gallery is not low, but the oil pressure sensor is reading low, the sensor is most likely faulty and needs to be replaced. A mechanic can check for loose or broken connections to the sensor. If the oil is low, mechanics can look for signs of oil leaks.
How to Detect Oil Pressure Sensor
The detection method of the oil pressure sensor: the pressure of the oil pressure sensor has a linear relationship with the output voltage, the pressure is from 0 to 10bar, and the output voltage is from 0.5 to 4.5 volts. How to determine the fault: first turn the ignition switch to OFF, unplug the harness plug of the oil pressure sensor, then turn the ignition switch to ON, and measure whether the voltage between the 3-pin A24 of the plug and the ground is the input voltage and whether the voltage between the pin 4 and the ground is zero.
Pressure sensors include silicon piezoresistive pressure sensors and silicon capacitive pressure sensors, both of which are micromechanical electronic sensors generated on silicon wafers.
Silicon piezoresistive pressure sensor uses high-precision semiconductor resistors and strain gauges to form a Wheatstone bridge as a power-to-electricity conversion measurement circuit, which has high measurement accuracy, low power consumption, and extremely low cost. For the piezoresistive sensor of the Wheatstone bridge, if there is no pressure change, its output is zero and consumes almost no power.
The MEMS silicon piezoresistive pressure sensor adopts the inner wall of the silicon film of the circular stress cup fixed around the periphery and uses MEMS technology to directly engrave four high-precision semiconductor strain gauges at the place where the surface stress is the largest to form a Wheatstone measurement bridge, which is used as a power-to-electricity conversion measurement circuit to directly convert the physical quantity of pressure into electricity, and its measurement accuracy can reach 0.01-0.03% FS.
The capacitive pressure sensor uses MEMS technology to manufacture a transverse barrier on a silicon wafer. The upper and lower transverse barriers become a set of capacitive pressure sensors. The upper transverse barrier is displaced downward by the pressure, changing the upper and lower barriers. The spacing of the grids also changes the size of the capacitance between the plates, that is, △pressure = △capacitance.
Symptoms of a Bad Oil Pressure Sensor
The oil pressure signal display indicates that the oil pressure of the engine is lower than the specified value, and the ECM considers it to be a fault and stores the fault in the form of fault code 415. At this time, because the oil pressure is too low, the protection function of the engine works, forcing the power and speed of the engine to drop, and possibly causing the engine to stall for protection.
After starting, the oil pressure indicator light is always on, the engine fault light is always on at idle speed, and the oil pressure value is displayed as 0.99. The fault code: P01CA (the oil pressure sensor voltage is higher than the upper limit)
How to Solve the Fault of the Oil Pressure Sensor?
There are some cases of faulty oil pressure sensors.
- The engine oil storage is too small, resulting in no oil or less oil in the lubrication system, resulting in low oil pressure.
Solution: add fuel.
- Dirty or viscous oil makes the oil pump unable to effectively inhale and pump out the oil, resulting in low or no oil pressure.
Solution: Change the oil.
- The oil is thin or the oil becomes thin due to high engine temperature, which will leak from the gaps of the friction pairs of the engine, resulting in low oil pressure.
Solution: Change the oil or overhaul the cooling system.
- Oil leakage from the oil pipe, damage to the oil pump, or excessive wear of its components will lead to reduced oil intake and pump output, or no amount at all, resulting in low or no oil pressure.
- The clearance between the crankshaft and the large and small tiles exceeds the standard, which leads to oil leakage, resulting in low oil pressure. Solution: Repair.
- The pressure limiting valve or pressure relief valve spring is too soft or the hairpin or steel ball is damaged, which causes the valve function to disappear or weaken, resulting in a decrease in oil pressure.
Solution: Replace and repair.
- The oil pressure is low due to the failure of the oil sensing plug, pressure gauge, or circuit.
Solution: Replace and check.