Can the automobile computer board be used for a long time after maintenance?

General maintenance will not be a problem within three years.

Fault analysis of automobile computer board

The most troublesome thing about repairing high-end cars is the on-board computer. When a repairman encounters a computer failure, firstly, he is afraid to conclude that it is a computer problem, fearing that he will easily decide to buy or replace the computer because of its high price; Second, it is not easy to find similar computer products for alternative testing; Third, even if we find similar computer products (such as cars of the same model), we dare not plug in a good computer board for testing, because the damage of computers is often caused by the failure of external circuits.

It is puzzling that when you ask the car electrician about the status of a certain circuit component, quite a few electricians will answer with "electricity has arrived" or "no electricity has arrived". If the level of maintenance electrician only stays in the state of "power on" or "power off", it is far from enough to maintain the computer and its control system of the car. Because to judge the fault of a component and its related lines, you should at least find out which line is connected with long-term power supply (+batt); Which line is connected to the power supply controlled by the ignition switch (+B); What is the power supply (+5V) provided by the computer? Which is a ground wire; What are the signal lines? For the signal line, you need to use the "logic" file of the digital multimeter to test the high and low levels, or use the "frequency" file to measure the signal frequency (Hz) in the running state. Of course, it is best to use an oscilloscope to check the signal waveform.

According to the experience and lessons of automobile computer board maintenance, the principle and maintenance method of automobile computer are briefly summarized and introduced, hoping to be beneficial to the majority of maintenance technicians.

First of all, we should have a general understanding of the internal structure of the automobile computer, which consists of the following parts:

1. Composition of automobile computer

1. 1 power supply section

It is used to filter and stabilize the power supply provided by cars and provide a stable DC power supply for computers.

1.2 central processing unit (CPU)

Generally, 8-bit or 16-bit processors are used in automobiles, which means that 8-bit or 16-bit binary numbers can be controlled, calculated and transmitted at one time, and they are the central command organization of computers.

1.3 memory section

Used to store programs and various data, which can be divided into:

1.3.l read-only memory (ROM)

Used to store computer monitoring programs, that is, some programs necessary for the operation of the computer itself.

1.3.2 programmable read-only memory (EPROM or EEPROM)

It is used to store the control program that makes the execution device or other control devices act. Such as fuel injection control and ignition advance angle control. Idle speed control and self-diagnosis procedures.

1.3.3 random access memory

Used for temporarily storing data from various sensors for use by the central processing unit; You can also store the fault code of the system. After the power is cut off, the contents in the RAM will disappear.

1.3.4 adaptive memory (a kind of random access memory) is used for "self-learning" of computers, and automatically adjusts relevant parameters according to the change of vehicle conditions. Such as "idle study".

1.4 input/output section

1.4. 1 input section

The analog signal from the sensor is converted into a digital signal (that is, ND conversion) for processing by the central processor. Some sensors transmit digital signals directly, so they don't need to be converted, but they need to be shaped, such as the signal of crankshaft position sensor.

1.4.2 output section

After receiving various signals from various sensors, the central processor processes them and then sends out corresponding control signals; Because the control signal is a digital signal, it must be converted into an analog signal (that is, D/A conversion) and then amplified by an amplifier circuit before the actuator can be driven. There are also some output signals that do not need to be converted and are directly amplified and output to the actuator. For example, the control of fuel injector is directly amplified by digital signal and added to the coil of fuel injector.

Before you start to repair the computer, you should first check the control circuit (external circuit) of the computer and eliminate the faults in the circuit. Because if the external circuit fails, it is easy to repair the computer by mistake. Even if the new computer board is repaired or bought back, the computer will be damaged again because of the failure of external circuit after installation and use. For example, a repair shop changed a Crown 28 car from right to left and tried to start it. After repeated inspections by several electricians, no problems were found, so it was suspected that the computer was damaged, but I was not sure. After checking the external circuit (because the car needs to change the direction, it is very likely to connect the wrong wires), it is found that there are two wires with the same color and wire diameter in the engine computer harness, one of which leads to the throttle position sensor and the other to the ignition amplifier, so it is suspected that these two wires may be connected incorrectly because of the same color and thickness. Open the computer case and check the computer pin abbreviations connected by two wires on the circuit board. It is found that one pin is "IDL" and the other is "IGL". IDL leads to the ignition amplifier and IGT leads to the throttle position sensor. At this point, it can be judged that these two lines are reversed and should be exchanged. Because "IGT" is the abbreviation of "IGNIROT" and "IDL" is the abbreviation of "IDLE" (idle speed, here refers to the idle contact of the throttle position sensor). After the two lines are connected, the engine runs normally. This example shows that the external circuit must be checked before the computer is overhauled or replaced, otherwise, it is easy to cause the good computer to be repaired or the new computer to be unable to troubleshoot, or even burn the new computer.

2. Computer failure

After troubleshooting the external circuit, if it is determined that the computer is damaged, the computer board can be overhauled. According to the author's rough statistics, 90% of damaged computers can be repaired. The following is the classification and maintenance of common faults in practical work:

2.l Computer power failure.

Generally, it is because the charger voltage is adjusted too high, or the polarity is reversed, or the key is turned on when charging, or even the motor is started, or the battery connector is loose during the engine operation, resulting in the generator directly supplying power to the computer board. In this case, the high-power zener diode and other components will be burned out, so it is easy to replace and maintain.

2.2 input/output component failure

Generally speaking, the amplifier circuit components are burnt out, and sometimes the steel wires on the circuit board are burnt out. For example, after an American Chevrolet car was refurbished and painted, the repair shop found that the engine could not be started, and gasoline would overflow from the exhaust pipe and oil pan if the key was turned on for a long time. When the key is turned on, it is found that all six fuel injectors are fully opened, and the gasoline directly flows into the cylinder from the fuel injector, and overflows when it is full. No problem was found in the external circuit, so it can be concluded that the output control in the computer is faulty. When the computer box is opened, it is found that a high-power triode that amplifies the control signal of the fuel injector has been broken down and short-circuited, resulting in the nozzle being in a normally open state when it is energized. Replace a triode with a similar model. After cleaning and replacing the oil, the engine can run normally. It should be noted here that many EFI vehicles often have various failures when they restart after painting. This is because after being painted, high temperature and heat accumulate in the vehicle, especially in the circuit equipment, which is slowly emitted from the deep inside, and electrical equipment is prone to failure when working at high temperature. Therefore, the car should not be driven out immediately after painting, but should be fully cooled before starting. If the spray booth needs to be vacated due to tight production, you can start the car manually and wait until it is fully cooled before starting.

2.3 Memory partial failure

There are four kinds of memory * * *, which can eliminate the problems of programmable memory (EPROM or EEPROM) and can be replaced. You need to find a known good memory chip with program content, buy a blank chip of the same model, read the program from the original chip through programming equipment, and then write it into the blank chip. You can copy a new chip and load it into the computer. The general automobile manufacturers have regulations that they can only copy it for 3-7 times at most, and they can't be used after the number of times. Some manufacturers can't encrypt and copy the chip once. For Volkswagen series cars, the original instrument 155 1 or the instrument developed by Shenzhen Jacky Company 1553 can be used to replace the computer program, or the program can be written into a blank chip.

2.4 Special fault

For flooded vehicles, the computer board will be corroded, resulting in broken needles, adhesion or component damage, so components can be repaired or replaced one by one. For example, Cadillac car is repaired in a repair shop. The fault phenomenon is that if the headlights or other electrical equipment are turned on/off when the engine is running normally, the exhaust pipe will explode, and in severe cases, the exhaust pipe will burst. After inspection, it was found that there was nothing wrong with the external circuit, and it was suspected that it was a computer fault. After opening the computer box and checking it carefully, it was found that one ground wire was broken due to corrosion. The grounding wire is the position where the signal shielding wire of the oxygen sensor passes through the internal grounding of the computer. Due to the open circuit, the shielding fails, which leads to the interference of the oxygen sensor signal by other electrical appliances. Return to normal after welding.