Automobile Inspection Technology

Chapter 22 Detection Technology of Automotive Electronic Control System (7)
④ If it is difficult to distinguish the shift position of L position, 2 position and D position, carry out the following road test: When the vehicle is running, after shifting from L position to 2 position, 2 position to D position, check the shifting of the corresponding gear position Variety.If abnormalities are found in the above test, it is a failure of the transmission mechanical system.

3. Stall test ([-]) purpose
The stall test is to check the overall performance of the engine and transmission by measuring the stall at D and R positions.

(2) Precautions
① Carry out the test at normal operating temperature (50-80°C, 122-176°F).

②The test shall not be carried out continuously for more than 5s.

③In order to ensure safety, please carry out on a wide level ground, and make sure that no one is in front of or behind the test vehicle.

④ The stall test should be completed by two persons.One person observes the condition of the wheel or the condition of the wheel jam, while the other performs the test.

(3) Test procedure
① Plug the front and rear wheels.

② Install a tachometer on the engine (this step can be omitted if there is a tachometer on the dashboard).

③Tighten the parking brake handle.

④Depress the brake pedal with your left foot.

⑤Start the engine.

⑥Place the gear selector in the D position.Depress the accelerator pedal to the bottom with your right foot, and at the same time quickly read the engine speed, which is the stall speed.

Note: If the rear wheels start to spin before the engine speed reaches the specified stall speed, the accelerator pedal should be released to stop the test.

⑦ Repeat the test at the R position.

The stall speed of the automatic transmission of common models is generally about 2200r/min, but the stall speed of some automatic transmissions is lower than 1800r/min, and the stall speed of some automatic transmissions is higher than 2800r/min.

(4) Analysis of test results
Different models have different faults due to different structures, and the test results reflect different faults. The following only takes the common Toyota four-speed automatic transmission as an example to illustrate.

① If the stalling speed at the two positions is the same, but lower than the specified value: the engine power may be insufficient, and the one-way clutch of the guide wheel (torque converter) is not working properly.

Tip: If the speed is lower than the specified speed value above 600r/min, the hydraulic torque converter may be damaged.

② Stall speed at D position is higher than the specified value: the main hydraulic pressure is too low, the forward gear clutch is not working well, and the 0/D one-way clutch is not working well.

③ Stall speed at R position is higher than the specified value: the main oil pressure is too low, the direct gear clutch slips, the first gear and reverse gear clutch slip, and the 0/D one-way clutch does not work well.

④ The stall speed at D and R positions is higher than the specified value: the main oil pressure is too low, the ATF liquid level position is abnormal, and the 0/D one-way clutch is not working well.

4. Purpose of gear shift time lag test
When the engine is idling and the gear selector is turned, there will be a period of hysteresis or delay before the vibration is felt. This is used to check the working conditions of the 0/D gear clutch, forward gear clutch, first gear and reverse gear brake, and direct gear clutch. .

(2) Precautions
① Carry out the test at normal working oil temperature (50-80°C, 122-176°F).

② Guarantee a 1min interval in each test.

③ Carry out three tests and take the average value.

(3) Test procedure
The test procedure is shown in Figure 4-46.

①Tighten the parking brake handle.

②Start the engine and check the idle speed.

③Turn the selection lever from N position to D position.Use a stopwatch to measure the time from when you toggle the lever until you feel the vibration.The delay time should be less than 1.2s.

④Measure from NR in the same way.The delay time should be less than 1.5s.

(4) Analysis of test results
①If the ND delay time is greater than the specified value: the main oil pressure is too low, the forward gear clutch is worn, and the 0/D one-way clutch is not working well;
②If the NR delay time is greater than the specified value: the main oil pressure is too low, the direct gear clutch is worn, the first gear and reverse gear brake are worn, and the 0/D one-way clutch is not working well.

5. Oil pressure test
The oil pressure test is generally the main oil pressure test, and it can also be used for the intake valve oil pressure, speed control oil pressure, and accumulator back pressure test.

(1) Precautions
① Carry out the test at normal working oil temperature (50-80°C, 122-176°F);

②Oil pressure test should be completed by two persons.One of them should observe the wheels and their chocking while the other performs the test.

(2) Test procedure
The test procedure is shown in Figure 4-47.

①Start the engine and let the temperature of the engine and transmission be normal.

② Pull out the inspection joint plug on the transmission case, and connect the pressure gauge.

③Tighten the parking brake handle and block the four wheels.

④Start the engine and check the idle speed.

⑤Depress the brake pedal with your left foot, and change the gear selector to the D position.

⑥Measure the main oil pressure when the engine is idling.

⑦Depress the accelerator pedal to the bottom.When the engine reaches the stall speed, quickly read the maximum pressure of the oil circuit.

Note: If the rear wheels start to turn before the engine speed reaches the stall speed, release the accelerator pedal to stop the test.

(3) Analysis of test results
①The oil pressure is higher than the specified value in any range: improper adjustment of the throttle cable, throttle valve failure, regulating valve failure, oil pump failure, 0/D gear clutch damage.

②Low oil pressure only at D position: D position oil leakage, forward gear clutch failure.

③Low oil pressure only at R position: R position oil leakage, direct gear clutch failure, reverse gear brake failure.

[-]. Reading and analysis of automatic transmission fault codes

There is a self-diagnosis circuit inside the computer of the electronically controlled automatic transmission, which can continuously monitor the faults of the automatic transmission control system during the driving process, and record the faults in the computer in the form of fault codes.Maintenance personnel can read out the fault codes from the computer according to a specific method to provide a basis for the inspection and maintenance of the automatic transmission control system.There are two ways to read fault codes: detector code reading and manual code reading.

1. Automobile computer detector code reading
There are two types of automotive computer detectors: special type and general type.The special-purpose computer tester is specially designed and produced by automobile manufacturers for their own automobiles with computers, as shown in Figure 4-48.Only by connecting the tester with the computer fault detection socket on the car and turning on the ignition switch, the car engine and automatic transmission can be easily checked.
The computer and control system of the gearbox and other parts are tested.This computer testing instrument is only used for specified models.The connection diagram of the computer tester and the fault detection socket is shown in Figure 4-49.

Universal computer tester, also known as car computer decoder, can detect computers of different models.As shown in Figure 4-50, the Scanner car decoder produced by Snap-on Company of the United States and the OTC car computer decoder produced by LAE Company of the United States are shown. This car decoder itself is also a small computer, and its software stores various The test program and data of the computer and control system of the vehicle model are equipped with various test plugs.When in use, just input the name of the manufacturer and the vehicle identification code of the car under test into the car computer decoder, and the corresponding detection program can be called out from the software, and then follow the detection steps displayed on the screen of the computer decoder to convert the corresponding The fault detection plug is connected with the computer fault detection plug on the automobile, and the computer and control system of various parts such as the automobile engine, automatic transmission, ABS, etc. can be selectively detected.

With the continuous updating of vehicle models, the car computer and control system are also constantly improving. Therefore, after a few years of use, a special or general-purpose car computer tester should be replaced with a new software card to improve the tester's detection capability. It can test the computers and control systems of various latest models.Dedicated or general-purpose automotive computer detectors have the following functions:

(1) Read the fault code

The automotive computer tester can easily read out the fault codes stored in the automatic transmission, and display the meaning of the fault codes, providing a reliable basis for checking the control system of the automatic transmission.

(2) Data transmission

The computers of many models transmit the instantaneous values ​​of various input and output signals (such as various sensor signals, computer calculation results, control modes, control signals sent by the computer to each actuator, etc.) In the way, it is sent out through a certain jack in the fault detection socket.The computer tester can display these values ​​on the screen of the tester in the form of a data table, so that the failure of the entire control system can be seen at a glance.Maintenance personnel can judge whether the control system is working normally according to the changes of various data of the control system during the working process of the automatic transmission, or compare the instructions of the computer with the actual response of the automatic transmission, so as to accurately distinguish whether the fault is in the control system Or in other parts of the automatic transmission.

The fault detected by the fault self-diagnosis circuit of the automobile computer will always be recorded in the computer as a fault until the automobile battery cable is removed.The computer tester can send instructions to the car computer to clear its stored fault codes.

2. Manual code reading
Automobile computer detectors are expensive. If you do not have such an automobile detector, you can use manual code reading.The manual reading methods of electronically controlled automatic transmission fault codes of different models are different.At present, the manual code reading method of most models is: use a wire to short-circuit the two specific jacks (fault self-diagnosis jack and ground jack) in the car computer fault detection socket, and then observe the automatic transmission on the instrument. The fault indicator light flashes regularly to read the fault code, and this method can be used for manual code reading of Japanese Toyota cars, American GM cars and Ford cars.

Before reading the DTC, keep the battery voltage normal.The shape of the fault detection socket of the automobile computer of different models and the distribution of the jack positions are different, but the manual reading method is basically the same.Taking the reading of fault codes of automatic transmissions of GM and Nissan as examples, the following introduces the operation methods of manual code reading for common models.

(1) Reading of fault codes of GM automatic transmission
The fault detection sockets of various cars (such as Cadillac and Chevrolet) produced by General Motors of the United States are generally located under the dashboard of the cab. As shown in Figure 4-51.Then turn on the ignition switch, you can read the fault code by observing the flashing pattern of the indicator light on the instrument panel, or use a voltmeter to detect the voltage pulse signal of the jack D in the socket. See Table 1991-4 for the fault code meanings and fault causes of various brands of GM automatic transmissions produced after 15.

(2) Reading of Nissan automatic transmission fault codes
Nissan vehicles do not have a test socket for automatic transmission DTCs.When reading the fault code, you can follow the steps below:

①Run the engine to normal operating temperature.

②Turn off the ignition switch to stop the engine.

③Press the switch at the 0/D position to make it "ON" and the shift lever to the "P" position.

④Turn on the ignition switch and put it in the "ON" position. At this time, the 0/D position indicator light "O/DOFF" or the mode indicator light "power" light up for 2s and then turn off the engine.

⑤Turn off the ignition switch.

⑥Turn the shift lever to the "D" position, and then set the 0/D position switch to the "OFF" position.

⑦Turn on the ignition switch, put it in the "ON" position, and after 2s, turn the shift lever to the "2" position.

⑧Put the "O/D" position switch to the "ON" position, and then turn the shift lever to the "1" position.

⑨Put the "0/D" bit switch to the first position.

⑩Put the "0/D" bit switch to "0N" position.

At this time, the computer enters the fault self-diagnosis state, and the fault code of the automatic transmission can be read out by observing the flickering pattern of the indicator light on the instrument panel.Table 4-16 shows the meaning and cause of fault codes of Nissan automatic transmission.

[-]. Detection of automatic transmission system

The automatic transmission is composed of a hydraulic torque converter, a gear transmission system, an electronic control system, a hydraulic control system, and a shift actuator.The automatic transmission is a relatively complex system, which should be detected and diagnosed according to the structural characteristics and fault phenomena of the automatic transmission.The purpose of systematic inspection of automatic transmission is to determine the technical status of automatic transmission, find out the cause and location of the fault, and take corresponding measures to eliminate the fault.

1. Routine testing

Most of the failures of automatic transmissions are caused by improper use and maintenance.Therefore, the basic detection and adjustment of the automatic transmission should be carried out first, which can not only solve some faults caused by improper maintenance, but also provide useful information for further fault diagnosis.

(1) Detection when the engine is idling

Detect whether the engine is at idle speed and the coolant temperature is normal, and when the automatic transmission is placed in the "N" position, whether the engine idle speed is within the specified range.If the idle speed is too low, when the transmission is placed in the "R", D, 2" or "1" position, the car will vibrate, which will affect the comfort of the ride, and in severe cases, the engine will be turned off.If the idle speed is too high, there will be shift shock.

(2) Detection of throttle cable

In the automatic transmission, the throttle cable is connected to the throttle valve and the throttle valve on the engine, and through the change of the displacement of the throttle valve, the throttle opening signal of the engine is converted into the oil pressure signal of the throttle valve.The detection of the throttle cable is mainly to detect whether the throttle opening, which represents the engine load, is correctly reflected to the throttle valve inside the automatic transmission.

(3) Detection of gear selection mechanism

The driver realizes gear shifting by operating the gear selection control valve.If there is a fault at the gear selection control valve, the automatic transmission cannot automatically

move to work.

First observe whether the transmission mechanism of the gear selection mechanism is deformed or interfered, whether the joints are fixed well, etc.; Whether the lever enters each gear is flexible and free, and whether the shift lever is in the correct position after entering the gear.

Detect the "N" position start switch to see if the engine can only be started when the transmission lever is in the "N" or "P" position, and whether the reversing light is only turned on when the transmission lever is in the "R" position, so that the reverse Light.

Check the 0/D bit control switch to see if the 0/D bit of the automatic transmission is normal.

Check the kickdown switch to see if the wires of the sensor circuit are well connected, whether the kickdown switch is installed and the throttle opening when the switch is turned on is normal.

Check whether the oil level of the automatic transmission is within the specified range.

2. Gear detection

Gear detection is to check whether the working condition of each gear of the automatic transmission is good, including manual gear selection, manual gear shifting, forward shifting, etc.

3. Component detection of electronic control system

Detect whether there are problems such as short circuit, open circuit, grounding and poor contact in the wiring harness wires and connectors of the electronic control system, and whether the electronic control components are damaged or invalid.The detection and methods of electronic control components vary according to different models. Here we mainly introduce some common faults and detection methods that may be caused by component damage.

(1) Detection by the first vehicle speed sensor

Damage to the vehicle speed sensor may cause the automatic transmission to only run in one gear, and cannot upshift or downshift.

Jump gears frequently.

First, visually check whether the sensor is damaged or deformed, and then use a multimeter to measure whether the resistance of the sensor coil is normal. The resistance value varies with different models, generally between several hundred ohms and several thousand ohms.

Shift solenoid valve detection

A malfunction of the shift solenoid valve will result in the inability to shift gears.Detect whether the coil is short-circuited, open-circuited or poorly connected.

(3) Oil pressure control solenoid valve
Measure the resistance value at both ends of the solenoid valve, generally 3-5n.Connect an adjustable power supply to both ends of the solenoid valve coil, change the voltage, and the solenoid valve core should move.

(4) Control switch detection

There are many control switches of automatic transmission, including overdrive switch, mode switch, gear switch, brake switch and kickdown switch.Generally, a multimeter is used to measure the continuity of the two terminals.The gear switch has multiple sets of contacts, which should be measured separately.

(5) Detection of oil temperature sensor

Detect whether the oil temperature sensor is short-circuited or open-circuited, and whether the resistance and temperature values ​​of the sensor are consistent with the standard.

(Section [-]) Detection of Electric Steering System (PSS)

Now take the electronic control power steering system of Toyota LEXUS sedan of Toyota as an example to illustrate the fault diagnosis process.

[-]. Circuit detection

转向柱的电控系统分两类：一种是动力倾斜/手动伸缩（电路图如图4-52所示），另外一种是动力倾斜/动力伸缩型(电路图如图4-53所示)。动力倾斜/动力伸缩ECU连接器端子见表4-17。动力倾斜/动力伸缩转向柱系统的故障征兆、故障部位及其检查顺序见表4-18。

①Remove the tilt and telescopic ECU with wire connectors, connect the positive pole of the voltmeter to ECU-B, and the negative pole to ECU-E. The reading on the meter should be the battery voltage. If it meets the requirements, go to fault phenomenon table 4-18 The next circuit check in.Otherwise, go to step ②.

②Use an ohmmeter to check the continuity between the ECU-E of the ECU connector and the grounding of the vehicle body. The reading of the meter should be 0n.If it does not meet the requirements, repair or replace the wiring or connector.If the requirements are met, proceed to step ③.

③Remove the DOME fuse in the No. 2 junction box, and use an ohmmeter to check the continuity between the fuses. If not, check all the wiring and components connected to the DOME for short-circuit problems; if the ohmmeter If it is turned on, check whether there is an open circuit problem in the wiring and connector between the tilt and telescopic ECU and the battery.

2. Detection of the actuator power supply circuit The actuator power supply circuit is shown in Figure 4-55.

①Remove the tilt and telescopic ECU with the connector, connect the positive pole of the voltmeter to the +B of the connector, and connect the negative pole to the terminal GND. The reading on the meter should be the battery voltage. If the reading meets the requirements, go to Fault phenomena Check the lower circuit in Table 4-18; if the reading of the meter does not meet the requirements, go to step ②.

(End of this chapter)