How to check the crankshaft position sensor (CPS)?
Modern cars are interweaving both a variety of mechanical parts and electrical systems. If everything is clear with the mechanics, many beginners do not understand the principles of car electronics operation. There are no big secrets. All issues are handled by the ECU (Electronic Control Unit). It gathers information from multiple sensors. On the basis of the received and processed data the right decision is taken. At the same time one of the most important monitoring devices is the crankshaft position sensor (abbreviation is CPS).
Purpose and main types
The main objective of the ECU is to provide information on the crankshaft correct operation, its direction of rotation and frequency. At the same time the principles of CPS work may vary (depending on the manufacturer), but the goals remain the same.
At present, there are several main types of sensors:
– Magnetic sensors. The peculiarity of their work lies in the performance of their functions without additional power. The CPS voltage is generated after passing of a special “tooth” through a magnetic field. In this case, the sensor can perform several functions, including speed control;
– Hall sensors. In these sensors electricity flows when alternating magnetic field is approaching to CPS. The main active element here is teeth of the synchronization drive. Just after their proximity to the magnetic field sensor receives electricity;
– Optical sensors. In cars with such types of sensors, special synchronization drives perform with special teeth or holes. Target disc should interrupt the movement of the strip between the LED light and the receiver. After receiving a corresponding signal, the ECU can determine the crankshaft position, its rotation speed and movement direction.
The main signs of sensors malfunction:
There are several ways to diagnose the CPS malfunction:
– Car dynamic characteristics get worse. At the same time, you should pay attention to the “Check engine” error indicator on the panel – it should be lighted;
– The engine speed begins increase or decrease arbitrarily;
– There is a clear knock while pressing the gas pedal;
– It is difficult to start the engine.
All of the above mentioned malfunctions indicate certain failures in the CPS correct operation. However, you should not change the sensor immediately. First of all, you need to troubleshoot the device and make sure it is really broken.
Before you start checking the crankshaft sensor, it must be removed. To remove it, you need to do the following steps:
– Remove the “minus” battery;
– Drop the sensor connector;
– Unscrew the locking bolt;
– Remove the sensor.
After that, you should make a unit external inspection to find a fact of obvious mechanical damage. Please, pay special attention to the look of switching pads and core. If there is an obvious contamination, they must be removed with a soft cloth (preferably pre dampen the cloth in gasoline or alcohol). Please note that the sensor contacts must be perfectly cleaned for the best operation.
In the process of checking please pay attention on the gap between the synchronization disk and the CPS itself. It should be in the range 0.6-1.5 mm. If an external examination shows no abnormalities, you can start more serious test:
– Ohmmeter (multimeter) method. You need to make sure that the sensor winding resistance is normal. Functioning winding must have a resistance of 550-750 ohms. If the coil sensor is damaged, the resistance is too low (coiled-circuit), or too high. Of course, such a test does not give 100% results. However, suspicion of a sensor failure can be at least partially confirmed or denied.
– The second method is more complex and more accurate. To perform the operation, you will need the following equipment: a device for measuring inductance, power transformer, digital voltmeter and a Megger. When performing measurements, it is important that the temperature in the room was at 20-23 degrees Celsius. To start using a Megger you need to measure the insulation resistance. The measurements must be carried out with 500 volts. The permissible option is up to 20 megohms.
Next you need to check the inductance. If the sensor is defective, this option must be at the level of 200-400 Hz. While measuring, a synchronization disk must be demagnetized. This can be done through the power transformer, which we have previously prepared. After the analysis, you can make the final choice about the CPS either correct work or the unsuitability for further use.
– The third method is considered the most accurate, but it can only be applied on specialized service stations. The main reasons are the need for the oscilloscope and the complexity of the analysis. To start measurements you should connect black probe of the test device to the car “minus”, and probe to the sensor input. The second probe must be connected to an analog of USB Autoscope II input. Then you should start the engine and analyze the signal at the CPS output. Now it is already possible to make accurate conclusions about the suitability of the sensor or its malfunction.
Please remember that the crankshaft position sensor has the most important functions in the car. To avoid problems when the first symptoms of trouble appear, you need to check the crankshaft position sensor performance regularly and replace it if necessary. Otherwise, you should not be surprised if your car will not start one day.