Fault diagnosis of electric control suspension sys

2022-08-14
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Fault diagnosis of the electronic suspension system of LS400 car

I. The basic composition of the EMS system of LS400 car

the electronicmodulatedsuspension (EMS) system can automatically adjust the performance of the suspension components according to the instantaneous driving conditions of the car, that is, it can detect the running conditions of the car through various sensors. When the ECU receives the steering and braking signals detected by the sensors, it can adaptively process the vehicle's roll A control system that tilts forward and backward and automatically adjusts the damping force of the shock absorber. Since the 1990s, Toyota Lexus (Lexus) ls400ucf10 series cars have been equipped with an electronic control suspension system (Figure 1), which is mainly composed of body height sensor, main throttle position sensor, steering sensor, height control compressor, exhaust valve, dryer, No. 1 height control valve, No. 2 height control valve, front suspension control actuator, rear suspension control actuator, No. 1 height control relay It is composed of No.2 height control relay, suspension ECU, stop lamp switch, LRC switch, height control switch, height control on/off switch, vehicle speed sensor and IC regulator

lrc switch (Lexus driving switch) is used to control the operation of suspension control actuator and automatically control the damping force of shock absorber and the spring stiffness of pneumatic cylinder. When the LRC switch is turned to the sport side, it is turned on, and the system enters the automatic control state of high-speed driving; When the LRC switch is turned to the norm side, it is disconnected, and the system enters the normal automatic control state

when the height control on/off switch is in the on position, the circuit is connected, and the electronic control suspension system can automatically control the body height; When the height control on/off switch is in the off position, the circuit is disconnected, and the electronic control suspension system does not carry out body height control. The height control switch is turned off when it is turned to the normal side and turned on when it is turned to the high side. When the suspension ECU detects the state of the height control switch, it will raise or lower the vehicle accordingly. The control circuit of the EMS system of LS400 car is shown in Figure 2

II. The control function of the EMS system of LS400 car

the electronic control suspension system of LS400 car mainly has three control functions: body height control, suspension stiffness control and shock absorber damping force control. Compressed air, which acts as a spring, is stored in the electric control suspension system, that is, air spring. The stiffness of the air spring and the height of the vehicle are automatically adjusted by the control system according to the driving state of the vehicle; The damping force of the shock absorber is also controlled by the control system to suppress vehicle attitude changes such as vehicle tilting, front bumping when braking, and rear sitting down during high-speed driving. See Table 1 for specific control items of LS400 car EMS system

III. inspection of the EMS system of LS400 car

(I) inspection of the height adjustment function of the car

when the tire inflation pressure meets the requirements (205/65zr15 or 205/65r1594v tires equipped with LS400 car, the standard tire pressure is 230kpa for the front wheel and 250kPa for the rear wheel), and the car is in the normal height adjustment state, start the engine and change the height control switch from the norm position to the high position, Check the time required to complete the height adjustment and the change of vehicle height. It takes about 2S from operating the height control switch to starting the compressor, 20s ~ 40s from starting the compressor to completing the height adjustment, and the change of vehicle height is 10mm ~ 30mm. When the vehicle is in the state of high height adjustment, start the engine, change the height control switch from high position to norm position, and check the time required to complete the height adjustment and the change of vehicle height. It takes about 2S from the operation of the height control switch to the start of exhaust, 20s ~ 40s from the start of exhaust to the completion of height adjustment, and the change of vehicle height is 10mm ~ 30mm. If not, further inspection should be carried out to determine the cause and location of the fault, and corresponding maintenance measures should be taken

(II) inspection of input signal

ls400 car EMS system input signal inspection is shown in Table 2. The purpose of this check is to check whether the signals from the steering sensor and the stop lamp switch are normally input to the ECU. Close the ignition switch and short circuit the inspection connector terminals ts and E1 in the engine room. If the diagnostic code stored in the memory is output after the terminal TS is connected to E1, it should be repaired; If there is no diagnostic code output in the memory, check the input signal. Each item of input signal inspection shall be checked according to the operation specified in Table 2. Observe the flashing mode of norm indicator light when the engine is in different states. Normally, when the engine is stopped, the height control norm indicator light will flash at an interval of 0.25s and continue to flash until the engine is running. Then, operate according to operation 2 specified in Table 2, and observe the flashing mode of norm indicator light when the engine is in different states. Normally, when the engine is stopped, the height control norm indicator light is always on. If the requirements are met, it indicates that the signal of the inspected system is input to ECU normally. During the above inspections, the control of damping force and spring stiffness stops, and the damping force and spring stiffness are fixed in the "hard" state, and the vehicle height control is still normal

(III) inspection of overflow valve

the inspection of overflow valve is to check the action of overflow valve by forcing the compressor to work. The steps are as follows: ① close the ignition switch, short circuit terminals 1 and 7 of height control connector, and force the compressor to work; Then pour 400g dry mixture between the two rollers ② after the compressor works for a short time, check whether the overflow valve releases air; Jiangxi Yabao Lithium Industry Co., Ltd., Jiangxi Dongpeng new materials Co., Ltd., Jiangxi Zhili Technology Co., Ltd., Hunan Jinwang bismuth Industry Co., Ltd. and Guixi Dayuan industry (Group) Co., Ltd. ③ turn off the ignition switch; ④ Clear the diagnostic code: when the compressor is forced to work, a diagnostic code will be recorded in the ECU. Be sure to clear this diagnostic code after completing the check

(IV) air leakage inspection

mainly check whether the joints of pipes and hoses have air leakage. First, turn the height control switch to the high position to raise the height of the car, then stop the engine, and add soapy water at the joints of pipes and hoses to check whether there is air leakage

(V) vehicle height adjustment

in order to ensure the normal operation of the vehicle height adjustment system, the vehicle height must be adjusted. First stop the car on a level ground and check the height of the car. If the height of the car is within the standard value range, it is not necessary to adjust the height of the car, otherwise the height of the car is adjusted according to the following steps: ① loosen the two lock nuts on the connecting rod of the height control sensor; ② Turn the bolt of the height control sensor connecting rod to adjust the length (each turn of the height control sensor connecting rod can change the height of the car by about 4mm); ③ When adjusting, pay attention to check whether the ruler of the height control sensor connecting rod and the multi curve reference inch are less than the limit value; ④ Pre tighten two lock nuts; ⑤ Check the vehicle height again until the vehicle height reaches the standard value range; ⑥ Tighten the lock nut according to the tightening torque requirements

IV. fault diagnosis of the EMS system of LS400 car

the fault self diagnosis system of the EMS system of LS400 car needs to use the indicator light to read the fault code, so it is necessary to check the indicator light first

(I) indicator light check

1 Turn off the ignition switch, and the high lamp will be on all the time

2 Check the hanging control indicator light (with sport sign) and height control indicator light (with norm or hi sign), which should be on for about 2S. When the suspension control switch on the automatic transmission (some on the instrument panel) is turned to the sport side, the suspension control indicator is still on. Similarly, when the height control switch is turned to the norm or high side, the corresponding height control indicator lamp norm or hi is also on

when the height control norm indicator flashes every 1s, it indicates that there is a fault code in the ECU memory. The suspension control system is faulty and should be further overhauled. During the inspection of the indicator light, if the fault shown in Table 3 occurs, the corresponding circuit should be checked and the fault should be eliminated

(II) diagnostic code check

1 Turn off the ignition switch

2. Short circuit the diagnosis box (tdcl) or check the terminals TC and E1 of the connector

3. Read the diagnostic code by observing the flashing rule of the height control norm indicator

4. If there is no diagnostic code output, check the TC terminal circuit. If the time interval of the indicator light flashing is equal, it means that the suspension control system is normal, and the self diagnosis system has not found any fault

5. After inspection, disconnect terminals TC and E1

6. There are two ways to clear the diagnostic code: ① with the ignition switch off, remove the ECU fuse in the junction box for more than 10s; ② With the ignition switch disconnected, connect terminal 9 and terminal 8 of the height control connector, and connect terminal ts and E1 of the inspection connector at the same time. Keep this state for more than 10s, then close the ignition switch and disconnect the above terminals

7. Check and repair the fault part, and then check it again according to the steps of reading the code. If the diagnostic code disappears, it indicates that the suspension control system is normal. The fault has been eliminated

(III) repair according to the fault phenomenon

if a normal code is displayed during the diagnostic code check and the vehicle electronic control suspension still has (repeated) faults, then remove each fault according to the fault phenomenon, and repair each circuit related to the fault phenomenon in the order given in Table 4 and table 5. If there is no abnormal phenomenon in the relevant circuit, but the fault still occurs, the last step should be to replace the suspension system ECU

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