Four Wheel Drive Control System (Diagnostics - Introduction): Overview Lexus IS III

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1. PRECAUTION FOR DISCONNECTING CABLE FROM NEGATIVE BATTERY TERMINAL NOTE: When disconnecting the cable from the negative (-) battery terminal, initialize the following system(s) after the cable is reconnected. System See Procedure Variable gear ratio steering system Refer to «INITIALIZATION [04/2013 - ]»(ref-665529-S01115916402014102400000) Air Conditioning System Refer to «INITIALIZATION [04/2013 - ]»(ref-665529-S01115916402014102400000)
2. TROUBLESHOOTING PRECAUTION When there is a malfunction with terminal contact points or part installation problems with parts, removal and installation of the suspected problem parts may return the system to the normal condition either completely or temporarily. In order to determine the malfunctioning area, be sure to check the conditions at the time the malfunction occurred, such as DTC output and Freeze Frame Data, and record it before disconnecting each connector or removing and installing parts. Since the AWD control system may be influenced by a malfunction in other systems, be sure to check for DTCs in the other systems.
3. HANDLING PRECAUTIONS When removing and installing the 4WD ECU assembly and each sensor, be sure to perform DTC output confirmation. When the 4WD ECU assembly is replaced with a known good one from another vehicle, it is necessary to perform initialization. Refer to «INITIALIZATION [04/2013 - ]»(ref-665560-S07569788152014102400000) HINT: When replacing the 4WD ECU assembly with a new one, it is not necessary to perform initialization.
4. CAN COMMUNICATION SYSTEM PRECAUTION The CAN communication system is used for data communication between each of the ECUs and sensors. If there is a malfunction in a CAN communication line, corresponding DTCs for the CAN communication line are output. If any CAN communication DTCs are output, repair the malfunction in the CAN communication line and troubleshoot the AWD control system. Since the CAN communication line has its own length and route, it cannot be repaired temporarily with a bypass wire, etc.
5. AWD CONTROL PROHIBIT MODE PROCEDURES FOR INSPECTION AND MAINTENANCE WARNING: Secure the vehicle with lock chains for safety. NOTE: When testing with a drum tester such as a speedometer tester, a combination tester for the speedometer and brake or a chassis dynamometer, or when jacking up the front wheels and turning the wheels, activate AWD control prohibit mode to prohibit AWD control. AWD Control Prohibit Mode: NOTE: After activating AWD control prohibit mode, check that "Check AWD System" is displayed on the multi-information display, and then perform inspection and maintenance. Make sure that the engine switch is off and the engine is stopped. Connect the Techstream to the DLC3. Turn the engine switch on (IG). Turn the Techstream on. Enter the following menus: Chassis / Four Wheel Drive / Utility / Control Mode Change. Chassis > Four Wheel Drive > Utility Tester Display Control Mode Change NOTE: When activating AWD control prohibit mode, make sure the following conditions are met. The vehicle is stationary. The parking brake is applied. The shift lever is in P. The engine is idling. Follow the instructions on the Techstream screen and select "Prohibit mode" to activate AWD control prohibit mode. NOTE: If the engine switch is turned off and then turned on (IG) again during AWD control prohibit mode, AWD control prohibition is stopped and AWD control normal mode resumes. HINT: During AWD control prohibit mode, the front drive and rear drive ratio of the center differential is set to 3:7. After activating AWD control prohibit mode, check that "Check AWD System" is displayed on the multi-information display. AWD Control Normal Mode (Canceling AWD control prohibit mode) HINT: During AWD control prohibit mode, turning the engine switch off and then on (IG) again cancels AWD control prohibition making it possible to switch to AWD control normal mode. Check that "Check AWD System" is displayed on the multi-information display and that the vehicle is in AWD control prohibit mode. Enter the following menus: Chassis / Four Wheel Drive / Utility / Control Mode Change. Chassis > Four Wheel Drive > Utility Tester Display Control Mode Change NOTE: When activating AWD control prohibit mode, make sure the following conditions are met. The vehicle is stationary. The parking brake is applied. The shift lever is in P. The engine is idling. Follow the instructions on the Techstream screen and select "Normal mode" to activate AWD control normal mode. After activating AWD control normal mode, check that "Check AWD System" is no longer displayed on the multi-information display.

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COMMUNICATION TABLE

SYSTEM DESCRIPTION [04/2013 - ]

1. FUNCTION OF MAIN COMPONENTS Component Function Combination Meter Assembly Multi-information display (AWD warning) Displays a warning to the driver when the system is malfunctioning. Slip indicator light Notifies driver that the current road surface is slippery. Wheel Speed Sensors Detect the wheel speed of each wheel. Throttle Position Sensor Detects the throttle valve position and outputs it to the ECM. Park/neutral Position Switch Assembly Detects the shift position of the transmission and outputs it to the ECM. Stop Light Switch Assembly Detects when the brake pedal is depressed. Steering Sensor Detects the turning of the steering wheel. Transfer control solenoid assembly Controls hydraulic pressure of the center differential control limiting clutch using signals from the 4WD ECU assembly. 4WD ECU Assembly Detects the signals from each sensor via the skid control ECU (brake actuator assembly) to operate the transfer control solenoid assembly and control the system. ECM Outputs signals such as the shift position signal, throttle position signal, and other signals to the 4WD ECU assembly. Skid Control ECU (Brake Actuator Assembly) Detects the signals from each sensor and outputs them to the 4WD ECU assembly.
2. DRIVING FUNCTION Vehicle Condition Status Control at vehicle start up This controls the amount of sideways sliding that occurs at the rear of the vehicle when accelerating from a stop to improve acceleration and hill climbing capacity. Slip control at vehicle start up This helps prevent the vehicle from sliding sideways, to accelerate from a stop with the steering wheel turned and ensures a stable start up and steerability. Slip control This ensures high turning performance and stability which is not affected by road surface conditions during mid and high speed driving. Control during acceleration This controls straight-line driving when accelerating during mid and high speed driving to ensure straight-line stability of the vehicle.

See also:
• DIAGNOSIS SYSTEM [04/2013 - ]