The principle of operation of the steering wheel position sensor is quite simple. Consider this as an example of SAS mounted on BMW cars. The sensor consists of two potentiometers located at an angle of 90 °.
The readings from these two potentiometers cover one complete turn, fig. eleven
steering, all data from potentiometers are repeated after +/- 180 °. The SAS sensor understands this and accordingly calculates the steering speed. The full angle of the steering wheel position thus consists of the current potentiometer reading added to the number of full turns of the steering wheel in one direction or another. So that the exact position of the steering wheel is available at any time, there is a continuous monitoring of all movements of the steering wheel – even when the car is stationary. To achieve this, voltage is constantly applied to the angle sensor from terminal No. 30. This means that the steering wheel tracking continues even with the ignition switched off. The steering angle fixed by potentiometers remains available even after turning off the power; data on the number of steering wheel turns after a power failure is lost. In order for the steering angle sensor to understand the actual relative position of the steering wheel and the wheels of the car after the power supply is cut off, the control unit integrates software that can calculate this indicator based on the speed of the wheels of the car and the current reading of the steering angle. On some car models, it is enough to rotate the steering wheel 2-3 times to the right and left on a motionless vehicle. On others, adaptation of the SAS sensor is required. This procedure is possible both with the help of a diagnostic scanner and without it. If this procedure is not performed, the control unit cannot determine the exact relative position of the steering wheel and wheels. When the vehicle starts to move and reaches a speed of approximately 20 km / h, the corresponding DSC warning lamp will light up on the dashboard. The process of monitoring the state of the steering angle determination system starts immediately when the ignition is turned ON and if the steering speed is not known, the DSC system immediately switches to passive mode, and the corresponding DTC is written to the computer memory. On cars with a conventional single-axis drive, a situation is possible when, after the start of movement, the DSC control unit manages to calculate the correct steering angle at that moment the DSC warning lam on the dashboard will go out, and the system will begin to function normally. On all-wheel drive vehicles, the warning system works somewhat differently. DTC DTC is recorded immediately when power to the rudder position sensor (SAS) is interrupted. The system immediately switches to passive mode and when the ignition is turned on, the DSC warning lamp on the dashboard lights up, even on a stationary car.
But not only the power cut is the main cause of a malfunction in the system, additional checks of the proper state of the system are carried out periodically by the DSC control unit. The algorithm, as already mentioned above, is based on the readings of the ABS wheel speed sensors and the current values of the steering wheel position sensor SAS. In the memory of the DSC system EEPROM control unit, standard values are written that are compared with the current data from the sensors in real time. If the values do not match, then the system naturally switches to passive mode with all the ensuing consequences. Everyone who is engaged in car repair must have met with a situation when the wheels of the car are level, and the steering wheel is shifted to one or the other side. This is a prime example of a mis-calibration of the SAS sensor. Such a situation can arise both during normal operation of the car and during repair and maintenance work with steering elements of the car, as well as during service procedures for adjusting the geometry of the wheels.
Zero Point Calibration without the diagnostic scanner on Toyota vehicles is calibrated to zero position using the following algorithm.
The car should be on a flat surface with a slope of less than 1 degree. To be motionless. On cars with an automatic transmission, the gear selector must be in the “P” position and the parking brake is activated, on cars with a manual transmission, activate the parking brake. During the procedure, do not change the position of the steering wheel or rock the car. The wheels of the vehicle must be in the forward position..
1. Turn the ignition ON, but do not start the engine.
2. Using a jumper, connect and disconnect the Ts and CG contacts more than 4 times in the DLC3 diagnostic connector for 8 seconds, Fig. 12
3. Verify that the VSC indicator on the dashboard is flashing to indicate a previous calibration has been reset..
4. Turn off the ignition “OFF”.
5. Verify that the Ts and CG pins in the DLC3 diagnostic connector are disconnected..
6. Turn on the ignition ”ON”.
7. Verify that the VSC indicator on the dashboard lights up after turning the ignition on and goes out after about 15 seconds.
8. After 2 seconds after turning off the VSC indicator on the dashboard, turn off the ignition.
9. Use a jumper to connect the Ts and CG contacts to the DLC3 diagnostic connector.
10. Turn on the ignition ”ON”.
11. After turning on the ignition, make sure that the VSC indicator on the dashboard lights up for 4 seconds after turning on the ignition, and then starts to flash at intervals of 0.13 seconds.
12. Wait approximately 2 seconds while the VSC indicator on the dashboard flashes and turn off the ignition.
13. Remove the jumper from the DLC3 diagnostic connector.
14. Make a test drive by car for 5 minutes to ensure that the zero position calibration of the Steering angle sensor is successful. When you turn on the ignition and start the engine, the VSC indicator on the dashboard should light up briefly and turn off.
If during the test drive the VSC indicator on the dashboard lights up again, this means that the SAS zero calibration failed or the system has a malfunction. Try the calibration procedure again. If it also fails, check the system with a diagnostic scanner for DTCs.
Also, the category of basic sensors of electronic systems for additional safety of the car should include speed sensors WSS ABS systems installed on each wheel of the car. As the ABS system evolved, the type of sensors used changed, and if at the very beginning it was simple inductive sensors, which gradually replaced Hall sensors, which now in turn have to give way to new, more advanced MRE sensors. Our colleague Mikhail Evgenievich Kudryavtsev, the address of the article on the Internet autodata.ru/article/all/nissan_pathfinder_2007_mre_sensor/, described very well and in detail the principle of their action in his article “Nissan Pathfinder 2007 MRE sensor open circuit in the ABS harness”
I would also like to add that the waveform of the MRE sensors changes depending on the direction of the vehicle (forward / backward) and the signal is not taken from a conventional ring gear, but from a disk with magnetized fragments of different polarity.
What should significantly increase their reliability and accuracy of readings, Fig. thirteen
The main sensors of electronic systems of additional safety of the car, fig. 14
For service and repair, it is sometimes necessary to disable electronic safety systems. On many models, you can turn off by selecting the appropriate switch position on the dashboard located in the area, selecting the appropriate ON / OFF position. But not on all models such a switch is provided, and for example on the new Toyota camry there is a special procedure for turning the service mode on and off. In this mode, the TRC and VSC systems can be forcibly turned off either using a portable diagnostic tool or by simultaneously applying the parking brake and depressing the brake pedal. Information on changes in service mode can be found in the following maintenance recommendations..
Switch to service mode (TRC and VSC systems off).
TRC and VSC systems can be turned off in the order described below:
• Using the parking brake and brake pedal:
1. Make sure the ignition is off and the gear lever is set to ”P”.
2. Turn on the ignition (ON) and start the engine..
3. Perform steps 4 to 8 within 30 seconds after starting the engine.
4. Apply the parking brake..
5. Press the brake pedal twice and release it.
6. Turn the parking brake on and off twice by depressing the brake pedal.
7. Press and release the brake pedal twice while the parking brake is applied. Note: each of items 6 and 7 should be completed within 15 seconds..
8. Make sure that the slip warning lamp ”Slip” and the message ”CHECK VSC SYSTEM” are turned on on the multi-information display. Otherwise, repeat the procedure from step 1.
9. Electronic safety systems TRC and VSC can be returned to normal operation by turning the ignition off.
• When using a portable diagnostic tool:
1. Make sure the ignition is off and the gear lever is set to ”P”.
2. Turn on the ignition (ON) and start the engine..
3. Connect the portable diagnostic tool to the DLC3 connector and turn off the TRC and VSC systems from the corresponding service menu.
4. Electronic safety systems TRC and VSC can be returned to normal operation by turning the ignition off.
Diagnostics of electronic safety systems on the example of Toyota cars.
When an ECU detects electronic additional safety systems malfunctions in ABS systems with electronic brake force distribution (EBD), emergency brake assist, traction control (TRC) or directional stability control (VSC), the corresponding warning lamps and messages on the multi-information display indicate a faulty unit , fig. fifteen
In the event of a malfunction in the ABS, EBD and emergency brake booster systems, the TRC and VSC systems are disabled. Accordingly, the main indicator lamp and the slip indicator lamp “Slip” are turned on, and the message “CHECK VSC SYSTEM” is displayed on the multi-information display.
At the same time, electronic trouble codes (DTCs) are recorded in the system memory. DTCs can be read by the number of flashes of the ABS warning lamp or by the output of codes on the multimedia information display by connecting a jumper to the Tc and CG terminals of the DLC3 connector or using a diagnostic tool.
This system provides an active diagnostic mode for sensor signals. The function is activated by connecting a jumper to the Tc and CG terminals of the DLC3 connector or using a scan tool. The ABS warning lamp and VSC warning lamp flash at intervals of 0.25 s. This monitoring function checks the deceleration sensor, yaw sensor, brake master cylinder pressure sensor and speed sensor.
An example of information output on a multi-information display, fig. 16
The system status code is displayed. The DTC is displayed.
In case of certain malfunctions, the operation of electronic additional safety systems goes into emergency mode. Here are some reasons for such a transition..
• In the event of a malfunction of the ABS system and / or the emergency brake booster, the ECU of the electronic additional safety systems blocks the inclusion of additional brake systems (ABS, emergency brake booster, TRC, VSC).
• In the event of a malfunction of the electronic brake force distribution (EBD) system, the ECU of the electronic safety systems blocks the operation of this system. Even in this case, the effective operation of the brake system is ensured, with the exception of additional brake systems (ABS with EBD, brake assist, TRC, VSC).
• In the event of a malfunction of the Traction Control System (TRC) and / or the Stability Program (VSC), the electronic control unit blocks the inclusion of these systems.
• In the event of a malfunction in the communication line between the ECU of the electronic safety systems and the steering angle sensor, the yaw and deceleration sensors or the engine ECU, the ECU of the electronic safety systems blocks the functioning of the traction control system (TRC) and the exchange rate stability (VSC) system.
• If the engine ECU registers certain DTCs (this list varies by model and year of manufacture), then it blocks the functioning of the traction control (TRC) and the electronic stability control (VSC).
Also, in certain cases, when critical DTCs are detected (from the point of view of the car manufacturer), not only the TRC and VSC electronic safety systems can be disabled, but also a forced power reduction occurs through direct control to the throttle motor directly from the engine ECU to limit the maximum engine speed. The so-called mode “LIMP MODE”.
The power limitation mode is also activated in extreme situations arising on the road and when the TRC and VSC systems are turned on. When you turn on the VSC system of directional stability, the ECU of the electronic safety systems sends a VSC enable signal to the engine ECU.
Upon receipt of this signal, the engine ECU adjusts the throttle position to change engine power, Fig. 17
Well, in conclusion, very briefly about what the ABS system is with the electronic brake force distribution (EBD) system.
The ECU of the electronic safety systems calculates the speed of each wheel, the deceleration rate, and also recognizes the wheel lock based on signals from the wheel speed sensors, the vehicle’s rotation speed and the deceleration. Depending on whether the wheels slip or not, the ECU of electronic safety systems regulates the brake fluid pressure in the working cylinder of each wheel, including the check and pressure valves in one of three modes: decrease, hold and increase pressure.
The table shows a good example of an ABS system with electronic brake force distribution (EBD) in various operating modes. Fig. 18
Of course, this is not complete information about the structure and functioning of the additional safety systems of the car ABS, TRC and VSC, but just a thesis overview of the main points. To learn more deeply and how to understand it is possible only through the daily practice of working with these systems in the repair and maintenance of cars.
Successful to all repairs and trouble-free maintenance of their cars.
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