Automobile Inspection Technology

Chapter 16 Detection Technology of Automotive Electronic Control System (1)
Knowledge points
1. Instruments commonly used in the fault detection process of automotive electronic control systems;
2. Basic knowledge of fault detection in automotive electronic control systems;

3. Detection of automobile electronically controlled fuel injection system;
4. Detection of automobile electronically controlled automatic transmission system;
5. Detection of automobile electronically controlled steering system (PPS);
6. Detection of automobile anti-lock braking system (ABS).

Learn
1. Understand the use of some common tools in the fault detection process of the electronic control system; the basic procedures and precautions of fault detection;
2. Familiar with the detection parameters of the multimeter when testing the car; the characteristics and functions of the OBDn on-board diagnostic system;

3. Master the detection of each component of the electronically controlled fuel injection system; the basic inspection of automatic transmission and the analysis and processing of test content, methods and detection data; the meaning of the fault code read by the ABS electronic control system;

4. Learn the use of special detectors for electronic control faults; methods of reading and clearing fault codes of various electronic control systems in various models; detection of electronically controlled fuel injection, automatic transmission, ABS, and PSS systems.

With the acceleration of mechatronics in the automobile manufacturing industry in recent years, various electronic control systems such as engine management systems, integrated electronic chassis systems, and active body control systems are widely equipped in automobiles.When people are enjoying the comfort brought by high-tech electronic technology, the detection and diagnosis of various new automotive electronic control systems are gradually placed in front of the majority of automotive maintenance personnel.How to quickly, effectively and accurately diagnose the fault symptoms of these high-tech electronic control systems is a common concern of people in the automotive maintenance industry.

(Section [-]) Common Utensils and Instruments

When overhauling automobile faults, it is often necessary to use some tools and testing instruments.Before use, you must understand its performance and use precautions, and master the correct use method.Automotive electronic control systems are very sensitive to high temperature, high pressure, and high humidity. Therefore, repairs and tests are not allowed during the diagnosis and maintenance process to prevent tools, instruments, and equipment from being damaged.The following tools are commonly used in maintenance.

[-]. Jumper wire
As shown in Figure 4-1, it is a jumper wire. A simple jumper wire is a multi-strand wire, and its two ends are respectively connected with alligator clips or different types of plugs and probes. It can also be connected to a car fuse in the middle of the jumper wire. Plug for testing fuse holders.Multiple styles of jumper wires must be available for testing, for location-specific measurements.

Although the jumper wire is relatively simple, it is a very practical tool, and its function is only to act as a bypass circuit.It is mainly used for the inspection of circuit faults (open circuit, short circuit and electric channeling).For example, when the control switch is turned on and the electrical appliance is not working, the jumper wire can be connected between the "ground" terminal of the component under test and the body ground, and if the electrical appliance resumes working.If the jumper is connected to the "+" of the battery and the "power" terminal of the component under test, and the component works normally, it means that the power circuit is faulty; if the power circuit and the ground circuit If the electrical appliance still does not work, it means that the electrical appliance itself is faulty.In addition, in the self-diagnosis of the electronic control management system, jumper wires are commonly used to complete the process of "activating" the fault code (jumpered to the socket or plug specified in the special detection interface).

Precautions when using:
①Before adding the power supply voltage to the test components with a jumper wire, the specified value of the power supply voltage of the component under test must be confirmed, otherwise, the equipment may be damaged.

②The jumper wire should not directly connect the "+" terminal of the component under test with the engine or body ground, so as to avoid short circuit of the power supply.

[-]. Test lights
The test lamp is also called the test pen, which is based on the jumper wire and adds a lamp for displaying the conduction state of the circuit. According to the brightness of the lamp, the voltage of the circuit under test can also be judged.The test lamp can be divided into two types: active test lamp (can be replaced by resistance meter) and passive test lamp (can be replaced by voltmeter), and its composition is shown in Figure 4-2.

1. Passive test lamp

Passive test lamp is also called 12V test lamp. When there is a fault in the electrical appliance, first connect the grounding clip of the test lamp to the iron, and use a probe to short-circuit the "power" terminal of the electronic device. If the lamp is on, it means that the circuit under test is open. , should be successively short-circuited at the second test point, the third test point... until the light is on along the current flow direction.At this time, it can be concluded that the fault point is on the circuit or electronic device between the last two test points.

2. Active test light

The structure and principle of the active test lamp is basically the same as that of the passive test lamp, but the detection method is slightly different due to its own power supply.In addition, the circuit method can be used to quickly check the open circuit fault of the circuit.If it is connected across the two ends of the tested circuit and the test light is not on, it is preliminarily determined that the tested circuit is faulty, and the test range is gradually reduced until the test light is on, indicating that the breakpoint is between the last two measured points. in the circuit.

[-]. Multimeter
The multimeter can be used to measure the electricity and components in the circuit.Commonly used multimeters can be divided into two types: digital multimeter (DMM) and analog multimeter (analog meter).A multimeter is an essential instrument for fault diagnosis and detection of automotive electrical equipment.For traditional cars, to measure parameters such as voltage, current, and resistance in the circuit, an ordinary pointer multimeter can be used.However, modern automobiles generally adopt electronic control technology, and use low-impedance pointer multimeters, which are easy to cause damage to on-board computers and sensors.Therefore, it is best to use a high-impedance digital multimeter.The digital multimeter has the characteristics of high precision, fast measurement speed, early input impedance, wide range, strong overload capacity, strong anti-interference ability, low power consumption, and high resolution.

In the detection and fault diagnosis of automotive electronic control systems, in addition to the voltage, current, and resistance parameters, it is also necessary to detect parameters such as speed, dwell angle, frequency, pressure, time, capacitance, inductance, and temperature.These are of great significance to the fault detection and diagnosis of automotive electronic control systems.However, these parameters cannot be detected with a general digital multimeter, and an automotive multimeter must be used.In addition to the function of digital multimeter, the car multimeter also has the function of car professional items.

①Measure AC and DC voltage.Considering the allowable variation range of the voltage and the possible overload, the automotive multimeter should be able to measure the voltage value greater than 40V, but the measurement range should not be too large, otherwise the accuracy of the reading will decrease.

② Measure the resistance.The automotive professional multimeter can measure the resistance of 1Mn, and it is more convenient to use with a larger measurement range.

③ Measuring AC and DC current.The car multimeter can measure the current of 10A, if it is equipped with a clamp ammeter, it can measure the large current.

④ Measure the temperature.After configuring the temperature sensor, it can measure the coolant temperature, exhaust gas temperature and intake air temperature, etc.

⑤ Measure the performance of the diode.

⑥Measure the frequency of the electrical signal output by the sensor.

⑦ Measure the duty cycle of the pulse waveform and the dwell angle of the ignition coil.This function is used to detect the working status of fuel injector, idle speed stability control valve, EGR solenoid valve and ignition system.

⑧Measurement speed.

⑨Simulation bar display.The change function is used to observe continuously changing data.

⑩Peak hold, reading hold (data lock), memory maximum and minimum.This function is used to check the momentary failure of a certain circuit.

Measure capacitance, pressure, time, semiconductor components, etc.

Output pulse signal.This function is used to detect the failure of the distributorless ignition system.

[-]. Vacuum measuring instrument
In the automotive electronic control system, many actuators use the vacuum degree of the intake manifold as the power source, and the vacuum diaphragm is used to execute
The device realizes the control action.Therefore, when diagnosing, it is necessary to use a vacuum measuring instrument to apply a standard vacuum signal to the actuator to check whether they are working well, so as to determine the fault.As shown in Figure 4-3, it is a commonly used handheld vacuum measuring instrument.

Precautions when using a handheld vacuum gauge:

① Before testing, first make sure that there is no vacuum leakage at the connection, otherwise the measurement result will be inaccurate.

② When connecting the vacuum measuring instrument and components, choose a hose with a suitable diameter.Inaccurate vacuum readings, or no readings at all, when the inner diameter of the hose is greater than the outer diameter of the measured part, pipe or connection; when the inner diameter of the hose is smaller than the outer diameter of the measured part, pipe or connection Installation will cause damage to the spout, so that it cannot be used next time.

③Establish the vacuum according to the specified range, and it should not be too large, otherwise it will cause damage to the components or systems under test.

④ After the inspection, before disconnecting the connecting hose, the vacuum in the measuring instrument should be released first, and then the hose should be removed.Otherwise, dust, moisture, etc. will be sucked into engine components or related systems, causing adverse consequences.

[-]. Fuel pressure gauge
In the engine fuel injection system, the fuel pressure is the key factor to determine the fuel injection quantity, and it is also one of the important related parameters.The fuel pressure gauge is a professional tool used to measure the fuel pressure and is an important tool used in the inspection of the fuel injection system. In the electronic control of the engine management, the multi-point injection method is widely used, and there is usually a dedicated fuel pressure tester on the fuel main pipe. The interface, as shown in Figure 4-5, is tightened with bolts, and a check valve is installed inside to prevent dust from entering the fuel main pipe and high-pressure fuel from overflowing from the detection interface.When checking the fuel pressure, remove the bolt, connect the pressure gauge to the detection port with the corresponding joint and hose, and tighten the joint.Start the engine and read the fuel pressure gauge.The measurement range of the dedicated fuel pressure gauge is generally 6.9-690kPa.

[-]. Automatic inspection and cleaning analyzer for fuel injectors
After the injector is clogged, the mixture will become thinner and the injection shape will be worse, which will affect the working performance of the engine.Therefore, it must be checked and cleaned regularly.

1. Off-board injector washer

The fuel injector automatic detection and cleaning analyzer shown in Figure 4-6 is an off-vehicle type fuel injector cleaner. In addition to cleaning the fuel injector with ultrasonic waves, it can also be used to detect the fuel injector workmanship. condition and jet quality.It simulates the driving waveform output by the central control computer (ECU) of the engine, and drives the injector after being amplified. The fuel injector performs data detection and comparison detection.

Items that can be detected by the fuel injector automatic detection and cleaning analyzer Idle speed condition detection, maximum power condition detection, maximum speed condition detection, dynamic scanning detection, repeatability detection, physical cleaning (detection cleaning, recoil cleaning and ultrasonic cleaning) and chemical cleaning (cleaning with slightly acidic cleaning solution).

The analyzer can clean eight fuel injectors at the same time within 10 minutes, and complete leak detection and flow measurement and other items.

2. On-vehicle injector washer, as shown in Figure 4-7, is an on-vehicle injector washer. Its biggest advantage is that it can be cleaned on the vehicle without removing the injector.The washer is equipped with carbon remover and an electric fuel pump (20V AC). When cleaning, connect the connection main pipe of the washer to the oil pressure detection joint on the main pipe of the electric fuel pump, and connect the oil return pipe of the oil pressure regulator to the washer. At the same time, disconnect the drive circuit of the oil pump, then connect the circuit of the washer electric fuel pump and start the engine, make the engine run for 2000 minutes at a speed of 10r/min with a decarburizer, stop the engine, and disconnect the electric fuel pump of the washer Circuit, cleaning work is complete.

Seven, special detector
It is a very effective detection method to use a special detector to assist in finding the fault source of the automobile electronic control system.At present, the special detectors in the auto repair industry are divided into two types: desktop and portable.
The fuel injector must be removed from the vehicle for cleaning.

The portable special detector has the advantages of easy portability, simple operation, etc., and can greatly improve the speed and efficiency of maintenance, so it is widely used.These instruments generally have the following functions:

① Read the stored fault codes from the memory of the central control unit (ECU) of the electronic control system.

② When the engine is running or the car is running, the parameters of the electronic control system are dynamically detected.

③ After the inspection of the electronic control system is completed, clear the fault codes stored in the central control unit (ECU) according to the instructions of the maintenance personnel.

④ Automobile maintenance personnel can issue work instructions through the detector to detect the working conditions of each actuator when the car is running or parked.

At present, some engine computer testers imported from the United States have begun to be sold in China. Different testers are suitable for diagnosing and testing different engine computer control systems, but there are also ones that are suitable for various engine computer control systems, so-called comprehensive computer testing. instrument.Such as the computer tester sold by Owatonna Tool Company (OwatonnaToolCompany) in the U.S., which is called O D C Monitor (O D C Monitor), this tester is a liquid crystal screen, displayed in menu form, during detection, the operation control button selects The menu items are sufficient, easy to use, and clearly displayed.The diagnostic data transmission cable connected to the diagnostic socket is equipped with multiple interfaces, which are suitable for plugging into the diagnostic sockets of various models.There is a PROM socket at the end of the tester. When testing different car series, plug in the corresponding PROM magnetic card. The magnetic card is suitable for Chrysler (CHRYSLER), Ford (FORD) and GM (GM) car series, etc.If the engine microcomputer control system is improved, the test can be carried out only by using the magnetic card of the new revised version.Therefore, the tester can be applied to various car models manufactured in different years, and has a wide range of applications.

If the repair shop is a professional repair shop of a single car series, corresponding special detectors can also be selected, such as testing the VAG1552 of the German Volkswagen series, the DRBII (Diagnostic Readout Box) of the American Chrysler series and the STARII (Self-Test Automatic Readout) of the Ford series, etc. .The performance and usage of these special testers are basically the same as those of OTC monitors.Some can also be connected with personal computers and printers to greatly expand its functions.For details on how to use common professional testers, please refer to the product instruction manual, and will not repeat them here.

Eight, multi-function signal simulation detector
The typical feature of the instrument is to simulate the output signals of all sensors in the electronic control system to diagnose its circuit faults.It is also one of the important equipment in the inspection and diagnosis of the electronic control system.
For example, a certain fault code shows that the signal of the coolant temperature sensor is bad, but whether it is the fault of the sensor itself, or the fault of the circuit from the sensor to the central control computer (ECU) or the fault of the control computer (ECU) itself, further detection and diagnosis are required.Now the signal of the coolant temperature sensor can be simulated by the instrument to replace the signal of the coolant temperature sensor on the real vehicle, and input to the important control computer (ECU).If the engine works normally, it can be concluded that the coolant temperature sensor is faulty; if the fault symptoms do not improve significantly, the signal can be directly input from the corresponding terminal on the central control computer (ECU). It can be determined that the circuit from the coolant temperature sensor to the central control computer (ECU) is faulty; otherwise, it can be determined that the terminal of the central control computer (ECU) or itself is faulty.As shown in Figure 4-12, it is a special signal simulation detector for general vehicle series.

(Section [-]) Basic knowledge of electronic control system testing
[-]. Precautions for maintenance of electric control system

The automotive electronic control system is equipped with a central control computer (ECU), various sensors and actuators. It is a relatively complex computer control system. When checking and diagnosing the system, certain methods and steps need to be mastered.In addition, the system is very sensitive to high point pressure, high temperature, high humidity, and strong electromagnetic interference, so the following items must be paid attention to during use and maintenance.

① There must be sufficient basis for the judgment of the fault. Before the diagnosis, you must first find out the working principle and structure type of the faulty part, so that you can have a well-thought-out plan. There is a possibility of new malfunction or damage.

②Because most of the faults in the electronic control system originate from components such as sensors, actuators, and connectors, as well as obvious problems such as open circuit, short circuit, and loose connection plugs of components and wiring harnesses, these simple places should be eliminated first, and then Diagnose and eliminate faults in accordance with the prescribed methods and procedures for fault detection and diagnosis.In the electronic control system, the damage rate of electric fuel pump, idle speed control valve, throttle position sensor, oxygen sensor and coolant temperature sensor is relatively high.Don't easily suspect that the central control computer (ECU) is faulty, and don't easily remove the ECU box cover.Practice has proved that the possibility of ECU failure is very small, and the failure rate of ECU accounts for one thousandth of the total failure rate of the car within 10 kilometers.Therefore, only after confirming that all components are working normally can the ECU be judged to be faulty.

③The on-board diagnostic system can usually only provide fault codes such as short circuit, open circuit, or no output signal caused by damage to electrical devices related to the electronic control system, and cannot detect all types of faults in the control system, especially large-scale faults. Faults caused by precision errors of some actuators and sensors, so structural principle analysis and related actual parameter analysis are still the basis for judging faults. The specific cause of faults needs to be diagnosed intuitively and with the help of simple instruments, or even special testing equipment.

(End of this chapter)