Automobile Inspection Technology

Chapter 17 Detection Technology of Automotive Electronic Control System (2)
④Sometimes the meaning of the fault code is a sensor failure, but in fact it is a problem with the connection of the sensor or the connector, such as the aging of the connector, the loose joint or poor contact after repeated disassembly and assembly.Therefore, when disassembling and installing the components of the electronic control system, be careful not to damage the connecting lines, and ensure that the connectors are firmly inserted.

⑤ When the ignition switch is turned on and the engine does not start, the warning lights of some electronic control systems are normally on, and the lights should go out after a certain period of time or after starting the motor.If the warning light is still on, it means that the self-diagnosis system has detected a fault or abnormal situation in the system. According to the number of flashes of the warning light and the waveform of the output fault code, the fault of the electronic control system can be judged.

⑥Regardless of whether the engine is running or not, when the ignition switch is turned on, do not arbitrarily disconnect any circuit with electromagnetic coil devices, such as electromagnetic fuel injectors, idle speed control valves, ignition devices, secondary air injection solenoid valves, air conditioners, etc. Clutches, and battery cables that connect these devices, etc.Because any coil will generate instantaneous high voltage on the line due to self-inductance at the moment of power failure, sometimes it may exceed 7000V, which will often cause serious damage to the on-board computer and sensors.

⑦When performing arc welding on the vehicle body, the power supply of the central control computer (ECU) of each electronic control system should be disconnected first. The adaptability of the ECU to the ambient temperature is -22-+65°C. When repairing the body paint, the ECU should be removed or the heating temperature should be controlled.It is strictly forbidden to damage the sealing device of ECU or sensor or wash it with water.If the wiper leaks, it should be repaired as soon as possible to prevent the ECU installed on the lower wall of the engine compartment from being damaged due to moisture.

⑧When disassembling the electric wire connectors of the electronically controlled fuel injection system, first turn off the ignition switch, then remove the negative ground wire of the battery, and disconnect the battery.If you only want to check the electronic control system, just turn off the ignition switch without disconnecting the battery, otherwise all the fault codes stored in the electronic control unit will disappear, making it difficult to troubleshoot the engine.Therefore, if necessary, read the DTCs before disconnecting the battery.

⑨Modern cars also have vehicle anti-theft systems and audio anti-theft systems. If the battery cable is removed at will, the anti-theft system will work, or the audio system will be locked, causing unnecessary losses.Therefore, if you are not familiar with the condition of the vehicle, you should first ask the owner about vehicle anti-theft and audio anti-theft, and whether the owner knows the audio password before removing the battery.If the sound

If the car owner does not know the password but the battery has to be replaced, you can first use another emergency battery to connect the positive and negative wires to the positive and negative wires of the vehicle, then remove the battery on the car and install a new one on the car. After disconnecting the battery, remove the connecting wire of the emergency battery, so as to ensure that the vehicle is always powered.

⑩The central control computer (ECU) of the electronic control system has a learning function, but once the power circuit of the ECU is cut off (such as removing the battery), the data it stores during the running of the vehicle will disappear.Therefore, after re-connecting the power supply circuit (such as installing a battery), in order to allow the ECU to "recover memory", it is necessary to allow the ECU to re-learn and restore the learning function through road tests under different working conditions.

When overhauling the electronic components and sensors of the electronic control system, it is mainly to measure the voltage without unplugging the connector, so as to avoid new fault signals.Try to use special detectors for quantitative detection, motion detection and elimination of fault codes.If the electronic components and sensors are removed and installed, the ignition switch should be turned off (in the OFF position) to prevent the ECU from being damaged by the self-induced electromotive force.When disassembling, pay attention to loosen the locking spring or press the lock. When installing, insert it to the bottom and lock it.

Unless otherwise specified during the test, the pointer multimeter cannot be used to test the electronic control system ECU and sensors, and a high-impedance digital multimeter (or automotive professional multimeter) with an internal resistance greater than 10MO should be used for testing.

[-]. Electric control automatic diagnosis system

Modern automotive microcomputer control systems have fault self-diagnosis functions. When the system fails, the CHECKENGINE light (check engine warning light) is lit, and the ECU stores the fault information in the memory.Call out the fault code from the ECU through a certain program, quickly and accurately determine the nature and location of the fault according to the displayed content of the fault code, and check the relevant parts, components and circuits in a targeted manner to eliminate the fault.Therefore, calling fault codes to diagnose microcomputer control system faults is an important basic method for overhauling modern automobiles.After the fault is diagnosed and eliminated, the fault codes stored in the memory should also be cleared.Different models have different methods of calling and clearing fault codes.

1. Enter self-diagnostic test

When performing a self-diagnostic test, you must first enter the self-diagnostic test state. The method of entering the self-diagnostic test state varies according to different automobile manufacturers, and there are roughly the following types.

①Use a jumper wire to bridge the diagnostic input connector and the ground (ground) connector. Toyota vehicles use this method.

②Press the diagnosis button switch, this method is adopted for Volvo models.

③Turn the diagnostic switch on the microcomputer control device, this method is adopted for Nissan vehicles.

④ Simultaneously press the OFF and WARM keys on the air conditioner control panel, which is used by GM's Buick and Oldsmobile.

⑤ Ignition switch ON-OFF-ON-OFF-ON cycle once, the American Chrysler car series adopts this method.After the self-diagnostic test status is performed, different diagnostic test modes will complete different diagnostic test functions. Generally, there are two

Two diagnostic test modes: one is the static test mode, that is, the ignition switch is in the ON position, and the engine is tested without running.In this mode, it mainly extracts the fault codes of intermittent faults in the memory and the fault codes of faults in static test state.The second is the dynamic test mode, that is, the test is performed with the ignition switch in the ON position and the engine running.This mode is mainly to read the fault codes or monitor the composition of the mixed gas in the dynamic test state.The self-diagnosis system of some vehicles (such as Nissan's ECCS system) also has other diagnostic test modes, such as actuator monitoring mode and fault code clearing mode.

2. Display of fault codes
The self-diagnosis system controlled by the engine microcomputer mostly displays the diagnostic results in the form of fault codes. The meaning of the fault codes is explained in detail in the corresponding maintenance manual, so that the source of the fault can be easily found.Although various engine microcomputer-controlled self-diagnosis systems have their own characteristics in displaying fault codes, in summary, the most common display methods are as follows.

(1) Digital display
The digital display of fault codes has the characteristics of intuitive display and easy operation.At present, there are many applications in some high-end cars, such as Lincoln Continental (Lincoln Continental), Cadillac (Cadillac) and so on.During the self-diagnosis test, the fault code will be displayed in digital form on the information display screen of the combined instrument, generally on the temperature display screen, to perform the self-diagnosis test state, you should press the set control key, sometimes, you need to Press two or three control keys simultaneously.

(2) Pulse voltage display
Most of the microcomputer-controlled self-diagnosis systems of engines use pulse voltage display, that is, the signal of pulse voltage is sent out from the self-diagnosis output connector (STO), and the fault code is displayed by the blinking of the CHECKENGINE indicator light on the instrument panel. In some systems, the pointer voltmeter can be connected to the specified test connector in the diagnostic socket, and the fault code can be displayed by the swing of the pointer of the voltmeter.

There are generally four types of pulse voltage forms:

①Wide pulse means tens, and narrow pulse means ones.There is a short pause between tens and ones, and a long pause between fault codes.Figure 4-13 shows that the fault codes are 13 and 22.

②The voltage pulse width is the same, there is a short pause time between bits, and a long pause time between codes.

③ It means that the pulse width of the fault code is the same, there is a pause time between the bits, and there is a wider voltage pulse between the codes.

④ Use a voltage pulse of 5V to represent the tens digit, a voltage pulse of 0V to represent the one digit, and a longer one between codes.

(3) LED display
LED is the English abbreviation of Light Emitting Diode.Some manufacturers use one or more LEDs to display fault codes.These LEDs are generally installed on microcomputer control devices (computers), such as Nissan cars.There are also differences in how they indicate failures:

① When one LED is used, its indication method is the same as that of the fault indicator light on the instrument panel to display the fault code.

②When two LEDs are used, they are generally two light-emitting diodes of different colors. The red light-emitting diode displays the tens digit, the green light-emitting diode displays the ones digit, and the two LEDs jointly display the fault code.

③ When four LEDs are used for display, each LED represents 8, 4, 2, 1 respectively.When the fault code is displayed, add the codes represented by the lit LEDs to get the displayed fault code.

In addition, using the special detector for the engine microcomputer control system, not only can read the fault code directly from its LCD screen, but also can dynamically test the parameter values ​​of the sensors and actuators of the system, such as VAG1552 of German Volkswagen.

3. Clear the fault code
Generally speaking, the fault codes stored in the electronic control system can be cleared or cleared by disconnecting the power cord or fuse leading to the central control computer of the electronic control system.The fault code can also be cleared by unplugging the negative pole of the car battery or the fuse of the central control computer for about 30 seconds.However, it should be noted that removing the fault code by removing the negative pole of the battery will cause the memory of the quartz clock and audio devices to be cleared together.Therefore, when troubleshooting, it is best to follow the method indicated in the maintenance manual. Do not remove the negative pole of the battery at will, so as not to trigger the audio anti-theft system, causing the audio to be locked and causing unnecessary trouble.After clearing the fault code, turn on the electric control system again to see if the fault indicator light of the electric control system is always on or flashing.If it is still on, it means that there is still a fault in the system and further diagnosis is required.

[-]. OBDn on-board diagnostic system
1. Introduction of OBDn on-board diagnostic system
In the mid-1980's, the U.S. Environmental Protection Agency (EPA) instituted a policy mandating the use of on-board diagnostics (OBD) in all U.S. vehicles.A similar request from the California Air Resources Board (CARB) followed, advancing technologies such as diagnostic technicians' access to information stored in electronic control units (ECUs).The information related to the faults that have occurred and has been recorded and stored in the ECU memory is very helpful for fault diagnosis and correction.The main reason for this legislation is the requirement to reduce exhaust emissions.Its main objectives are:
① Improving emission levels while driving under fault conditions by immediately alerting the driver.

②Help maintenance/diagnostic personnel identify system failures and damaged components in the emission control system.

OBD tests are applied to the systems most likely to cause an increase in harmful exhaust emissions, namely all engine main sensors, fuel system, ignition system, exhaust gas recirculation (EGR) system.The system uses information from sensors to judge the performance of emissions controls, but these sensors do not directly measure vehicle emissions.

An important part of the system, and the main information interface for the driver, is the "check engine" warning light, also known as the Malfunction Indicator Light (MIL).This is the primary source of feedback to the driver, indicating whether a fault has occurred or exists.When a malfunction or problem occurs, the warning light illuminates to alert the driver.Furthermore, faults are stored in the ECU memory.If normal conditions are restored, the warning light goes off, but a record of the fault is kept to aid in diagnosis.Circuits are to detect open or short circuits and, as likely as possible, when a fault is detected, information about the faulty element is stored.

Another benefit of OBD is that it allows diagnostic personnel to obtain fault information and can monitor engine performance directly from the data output by the ECU while the engine is running (on some vehicles).The various diagnostic devices available on the market can acquire this information and communicate it in a standardized format, so the protocol with which a diagnostic device can address this data stream must be known in order to evaluate the information correctly.

The benefits of owning an OBD device are:

①It encourages vehicle and engine manufacturers to have a responsible attitude and reduce harmful emissions from engines by developing reliable and durable emission control systems.

② It can help diagnose and repair complex engine and vehicle electronic control systems.

③It reduces global emissions to the driver or user by immediately identifying and highlighting the need for maintenance of emission control systems.

④ It provides "whole life" emission control of the engine.

⑤ On-board diagnosis or OBD is the name of the early emission control and management system introduced in automobiles.There was no uniform standard at the time - each manufacturer usually used a completely different system (even between two individual car models). OBD devices have been developed and enhanced to the current OBDn standard, which also meets the requirements of the US government.Since 1996, the OBDn requirement has been applied to all cars sold in the United States. EOBD is the European version of the American OBDn standard. Since 2001, it has been applied to all gasoline engine cars sold in Europe (diesel cars are also applied after 3 years).

While new vehicles sold today emit far better emissions than their predecessors, the millions of cars on the road and the increasing number of miles they drive each day make them the single largest source of harmful emissions.Although a new vehicle may leave the factory with low emissions, infrequent maintenance or component failures can cause vehicle emissions to increase at an undesired rate. OBDn's job is to ensure that the vehicle remains as clean as possible throughout its lifetime.Therefore, the main characteristics of OBDn are as follows:
① When the critical value of emissions is exceeded, the failure of the components related to emissions is detected.

② Store faults and boundary conditions in the vehicle fault memory.

③Once there is a fault, the fault indicator light will be activated.

④ Read the fault code with a common diagnostic instrument.

2. Main features of OBDn on-board diagnostic system

①Unified diagnostic seat. The OBDn diagnostic socket is unified into a 16-pin diagnostic socket, as shown in Figure 4-17.

②Unify the position of diagnostic seat. The OBDH diagnostic seat is uniformly installed under the dashboard of the cab.

③ The fault codes of various vehicles are unified, and the meanings represented by the fault codes are unified. OBDH faults consist of 5 codes, as shown in Figure 4-18.

④DLC (DATALINK CONNECTOR) with numerical analysis data transmission function. There are two standards for OBDH data transmission lines:
a. ISOn European unified standard, terminals 7 and 15;
b. SAEII American unified standard (SAE-J1850), using terminals 2 and 10.

⑤ With the function of driving recorder, it can record the relevant data of the vehicle driving process.

⑥It has the function of monitoring emission control.

⑦ Each needle of the diagnostic seat tends to be standardized.The functions of each pin are shown in Table 4-1.

⑧Among the 16 pins of the OBDH diagnostic socket, 9 terminals are set by the car manufacturer. The meanings represented by different car manufacturers are shown in Table 4-2.

3. The method of reading and clearing the fault codes of vehicles using the OBDn system

For the main car series that adopt OBDH, the actual method of the diagnosis code can be displayed by a special detection instrument such as a decoder, or can be read on the car by the following method.

(1) GM general vehicle series
The way to read the engine fault codes for GM general vehicles is to jump over terminals 16 and 6 of the 5-pin diagnostic seat, and read it from the flashing "CHECKENGINE" light on the instrument panel.

(2) Ford Ford car series
The way to read the engine fault codes of Ford cars is to jumper the 16th and 13th terminals of the 15-pin diagnostic seat, and read it with the "CHECKENGINE" light on the instrument panel flashing.

(3)Chrysler Chrysler car series
The way to read the engine fault codes of Chrysler cars is to turn on the ignition switch, wait for about 5-10s, and then read out by the "CHECKENGINE" light flashing.

(4) BENZ Mercedes-Benz car series
BENZ Mercedes-Benz cars cannot read the fault codes from the OBDII diagnostic socket by jumping the test light, but can read the HFM engine computer fault codes from the 38th hole of the 4-hole diagnostic socket, or read the HFM engine computer fault codes from the 38th hole of the 19-hole diagnostic socket Get the DM computer fault code.

(5) Volvo Volvo car series

The way to read the engine fault codes for Volvo Volvo cars is to jumper the display light at the No. 3 terminal of the OBDn diagnostic seat, and read it according to the method shown.

(6) TOYOTA car series
The method of reading the engine fault codes of TOYOTA Toyota vehicles is to jump the OBDH diagnostic seat No. 5 and No. terminals or jump the TE1-E1 terminals, and read it from the flashing "CHECKENGINE" light on the instrument panel.

(7) Mitsubishi Mitsubishi car series
Mitsubishi Mitsubishi vehicles can read the fault codes of the following 5 systems from the OBDH diagnostic socket.

①Engine fault codes.To read the engine fault code, you can ground the No. 1 terminal of the OBDH diagnostic seat, and the "CHECKENGINE" light will flash.

(End of this chapter)