Power Steering: Other Lexus LS IV

PRECAUTION

Note. When disconnecting the cable from the negative (-) battery terminal, initialize the following system(s) after the cable is reconnected.

SYSTEM NAME CHART

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1. HANDLING PRECAUTIONS When handling the electronic parts: Avoid any impact to electronic parts such as ECUs and relays. Replace these parts with new ones if dropped or subjected to a severe blow. Do not expose any electronic parts to high temperature or humidity. Do not touch the connector terminals in order to prevent deformation or malfunctions due to static electricity. If the power steering ECU has been replaced with a new one, initialize the rotation angle sensor value and calibrate the torque sensor zero point (see «CALIBRATION»(ref-349733-S15208904932009120800000) ). When handling the power steering gear assembly: Avoid any impact to the power steering gear assembly, especially to the motor or torque sensor. Replace these parts with new ones if dropped or subjected to a severe blow. Do not pull on the wire harness when moving the power steering gear assembly. If the power steering gear assembly has been replaced with a new one, clear the rotation angle sensor calibration value, initialize the rotation angle sensor value, and calibrate the torque sensor zero point (see «CALIBRATION»(ref-349733-S15208904932009120800000) ). When disconnecting and reconnecting the connectors: Turn the engine switch on (IG), center the steering wheel, and turn the engine switch off before disconnecting the connectors related to the electric power steering system. Ensure that the engine switch is off before reconnecting the connectors related to the electric power steering system. After reconnection, center the steering wheel and turn the engine switch on (IG). NOTE: Do not turn the engine switch on (IG) when the steering wheel is not centered. If the above operations are not carried out properly, the steering center point (zero point) will deviate, which may lead to a difference in steering effort between right and left. If there is a difference in steering effort between right and left, perform steering zero point calibration (see «CALIBRATION»(ref-349733-S15208904932009120800000) ).
2. PRECAUTIONS FOR CAN COMMUNICATION CAN communication is used to receive information from the skid control ECU, power steering ECU, ECM and steering angle sensor, and to transmit warnings to the combination meter. It is also used for communication between terminals TC and TS of the DLC3. If there are any problems in the CAN communication lines, DTCs indicating communication line malfunctions are output. Perform troubleshooting for communication line problems if CAN communication DTCs are output. Be sure to start troubleshooting on the electric power steering system only when data communication is normal. Temporary fixing or repair with bypass wiring, etc. is impossible because the length and path of each CAN communication line is specified.
3. BUS LINE REPAIR After repairing the bus line with solder, wrap the repaired part with electrical tape. NOTE: The CANL bus line and CANH bus line must be installed together at all times. When installing, make sure to braid them. CAN bus lines are likely to be influenced by electrical noise if they are not braided. The difference in length between the CANL bus line and CANH bus line should be 100 mm (3.94 in.) or less. Leave approximately 80 mm (3.15 in.) loose in the braided wires around the connector. Do not use by-pass wiring between the connectors. NOTE: The ability of the braided bus lines to resist interference will be lost if by-pass wiring is used.
4. HANDLING PRECAUTIONS FOR SRS AIRBAG SYSTEM The vehicle is equipped with a Supplemental Restraint System (SRS). Failure to carry out service operations in the correct sequence could cause the SRS to unexpectedly deploy during servicing. This may cause a serious accident. Before servicing (including inspection, replacement, removal and installation of parts), be sure to read the precautionary notices for the Supplemental Restraint System (see «AIRBAG SYSTEM»(ref-349738-S32172982532009120800000) ).
5. PRECAUTIONS FOR REMOVAL, INSTALLATION AND REPLACEMENT OF ELECTRONIC MOTOR POWER STEERING COMPONENTS Be sure to align the front wheels straight ahead when removing and installing the power steering link. w/VGRS: If disconnecting the No. 2 steering intermediate shaft, steering sliding yoke and the pinion shaft of the power steering link, be sure to put matchmarks before starting the operation. w/o VGRS: If disconnecting the No. 2 steering intermediate shaft, steering sliding yoke, steering intermediate shaft and the pinion shaft of the power steering link, be sure to put matchmarks before starting the operation. After replacing the power steering link or power steering ECU, clear the rotation angle sensor calibration value, initialize the rotation angle sensor, and calibrate torque sensor zero point (see «CALIBRATION»(ref-349733-S15208904932009120800000) ).

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1. DESCRIPTION The electric power steering system generates assist torque to assist steering effort through the operation of the motor installed on the power steering gear assembly. The direction and amount of power assistance are determined by signals from the torque sensor, and controlled in accordance with vehicle speed. As a result, steering effort is controlled so that it is light during low speed driving and moderately high during high speed driving.
2. FUNCTIONS OF COMPONENTS FUNCTIONS OF COMPONENTS Components Function Power Steering ECU Calculates degree of assistance needed based on steering torque and vehicle speed. Drives the motor based on motor rotation angle obtained from the motor rotation angle sensor. Restricts power assistance to protect the system if the motor and ECU overheat. Power Steering Converter Assembly Boosts battery voltage to generate motor drive voltage. Torque Sensor Detect steering effort generated when the steering wheel is turned. Power Steering Motor Located coaxially with the rack shaft. Its rotation is converted to the rectilinear motion of the steering rack via the ball screw nut and ball. Motor Rotation Angle Sensor Detects motor rotation angle. Combination Meter (PS Warning Light) Upon receiving a signal from the power steering ECU in the event of a system malfunction, the meter ECU illuminates the PS warning light. Skid Control ECU Transmits speed sensor signals to the power steering ECU. ECM Transmits engine speed signals to the power steering ECU.
3. OPERATION EXPLANATION The torque sensor is mounted on the input shaft to the main shaft and on the output shaft to the pinion shaft. The input and output shafts are joined by a torsion bar. If the steering wheel is turned, the torsion bar twists, resulting in a difference in the rotation angle detected by the torque sensor. The power steering ECU calculates torque based on this difference. The power steering ECU calculates proper assisting torque, according to vehicle speed, based on the torque obtained in the previous step. Then the ECU controls the motor drive circuit in order to cause it to generate assisting torque. A ball screw nut is attached to the motor shaft. It converts the rotational motion of the motor into the rectilinear motion of the steering rack via the ball. The assisting force generated in the above process will reduce the steering effort required by the driver.

FREEZE FRAME DATA

1. FREEZE FRAME DATA NOTE: It is difficult to show the specified values (judgment values) clearly because freeze frame data values change significantly due to differences in measurement conditions, surroundings, or vehicle conditions. For this reason, there may be a problem even when the values are within specifications. Turn the engine switch on (IG) and park the vehicle on level ground. Check the freeze frame data by using the Techstream. Connect the Techstream to the DLC3. Turn the engine switch on (IG) and check the freeze frame data by following the prompts on the Techstream's display screen. EMPS DIAGNOSTIC NOTE Tester Display Measurement Item/ Range Normal Condition Diagnostic Note Engine Speed Vehicle speed from meter/ Min.: 0 km/h (0 mph), Max.: 255 km/h (158 mph) Vehicle is stopped: 0 km/h (0 mph) Vehicle is driven at a constant speed: No significant fluctuation - Engine Rev Engine revolution/ Min.: 0 rpm, Max.: 8,192 rpm Engine is running at a constant speed: No significant fluctuation - Motor Actual Amount of current to motor/ Min.:-128 A, Max.: 127 A Power steering is in operation: Value changes in proportion to steering effort When malfunction occurs, problem may be in steering system Command Value Demanded amount of current to motor/ Min.:-128 A, Max.: 127 A Power steering is in operation: Value changes in proportion to steering effort When malfunction occurs, problem may be in steering system Str Angl Vel Steering angle speed/ Min.: -4,096 deg/sec, Max.: 4064 deg/sec Steering wheel is turned: Value changes in proportion to steering speed - Thermistor Temp ECU substrate temperature/ Min.: -50°C, Max.: 205°C Equivalent to ambient ECU substrate temperature - IG Supply ECU power source voltage/ Min.: 0 V, Max.: 25.5 V Engine switch on (IG): 11 to 14 V - Trq1 Torque sensor 1 rotation angle/ Min.: 0 deg, Max.: 360 deg Steering wheel is turned: Value changes from 0 to 360° every 22.5° of steering angle When malfunction occurs, problem may be in torque sensor Trq2 Torque sensor 2 rotation angle/ Min.: 0 deg, Max.: 360 deg Steering wheel is turned: Value changes from 0 to 360° every 22.5° of steering angle When malfunction occurs, problem may be in torque sensor Trq1 Zero Val Zero point value of torque sensor 1/ Min.: 0 deg, Max.: 360 deg Steering wheel is not turned (without load) When malfunction occurs, problem may be in torque sensor Trq2 Zero Val Zero point value of torque sensor 2/ Min.: 0 deg, Max.: 360 deg Steering wheel is not turned (without load) When malfunction occurs, problem may be in torque sensor Steering Torque Steering torque/ Min.: -7.0 N*m, Max.: 7.0 N*m Steering wheel is turned: Value changes in proportion to steering effort When malfunction occurs, problem may be in torque sensor Motor Rotate Motor rotation angle/ Min.: 0 deg, Max.: 360 deg Steering wheel is turned: Value changes from 0 to 360° every 5° of steering angle When malfunction occurs, problem may be in rotation angle sensor Command Val 2 Amount of current demanded by motor 2/ Min.:-128 A, Max.: 127 A Power steering is in operation: Value changes in proportion to steering effort When malfunction occurs, problem may be in power steering motor. Motor Voltage Motor power source voltage/ Min.: 0 V, Max.: 64 V Power steering is in operation: 2 to 48 V - Mtr Terminal(U) Motor terminal voltage (U phase)/ Min.: 0 V, Max.: 64 V Power steering is in operation: 2 to 48 V When malfunction occurs, problem may be in power steering motor. Mtr Terminal(V) Motor terminal voltage (V phase)/ Min.: 0 V, Max.: 64 V Power steering is in operation: 2 to 48 V When malfunction occurs, problem may be in power steering motor. Mtr Terminal(W) Motor terminal voltage (W phase)/ Min.: 0 V, Max.: 64 V Power steering is in operation: 2 to 48 V When malfunction occurs, problem may be in power steering motor. Battery Voltage Battery voltage/ Min.: 0 V, Max.: 25.5 V 11 to 14 V - DC-DC Warning 42 V DC/DC converter warning signal/ OK or NG OK or NG - PS Assist Sig Power steering assist signal/ ON or OFF ON or OFF - Motor Actual 2 Amount of current to motor 2/ Min.: -327.68 A, Max.: 327.67 A Power steering is in operation: Value changes in proportion to steering effort When malfunction occurs, problem may be in power steering motor.

FAIL-SAFE CHART

If a problem occurs in the electric power steering system, the PS warning light will come on in the combination meter and steering power assistance will be stopped, fixed at a particular point, or decreased simultaneously to protect the system.

FAIL-SAFE CHART

HINT

1. With the vehicle stopped or driving very slowly, if the steering wheel is turned repeatedly or turned to a lock position and driven for an extended period of time, the power assistance amount is decreased to prevent overheating of the motor and ECU. If this occurs, idle the engine and do not turn the steering wheel for approximately 10 minutes to return the power assistance to normal.
2. If the battery has not been recharged enough or the voltage drops temporarily, the power assistance amount may be decreased and the P/S warning light may be illuminated. If this occurs, the power assistance returns to normal when the battery returns to normal. When troubleshooting malfunctions, use the Techstream to check for power load malfunctions through the electric power control system's load control history (see «DATA LIST/ACTIVE TEST»(ref-349733-S22152673862009120800000) ).