Power Steering System (Diagnostic Codes & Circuit Tests): Overview Lexus IS III

DESCRIPTION

The power steering ECU assembly receives signals from the ECM, skid control ECU (brake actuator assembly), VGRS ECU (front steering control ECU) and AVS ECU (absorber control ECU) via CAN communication.

When an incorrect ECM, AVS ECU (absorber control ECU) (w/ Adaptive Variable Suspension System) or VGRS ECU (front steering control ECU) (w/ Variable Gear Ratio Steering System) is installed after the assist map has been written to the power steering ECU assembly, then DTC C1582 is stored because the data does not match the vehicle specifications.

This DTC will be stored if the power steering ECU assembly determines that the assist map is not written in the ECU.

Based on the steering angle sensor signal, the power steering ECU assembly determines if the correct type of steering angle sensor is installed.

The power steering ECU assembly supplies current to the power steering motor.

Scheme 31

If a problem occurs in the system, the power source relay circuit and the motor relay circuit are shut off to stop the power assist. The ECU must be replaced when there is a problem with the relays because the relays are built into the ECU.

Scheme 32

The power steering ECU assembly distinguishes the engine switch status as on (IG) or off through the IG power source circuit.

Scheme 33

The power steering ECU assembly sends and receives steering cooperative control information to and from the skid control ECU (brake actuator assembly) and VGRS ECU (front steering control ECU) via CAN communication.

The power steering ECU assembly receives vehicle speed signals from the skid control ECU (brake actuator assembly) via CAN communication. The ECU provides appropriate assist force in accordance with the vehicle speed based on the signals.

The motor rotation angle sensor detects the motor rotation angle and sends this information to the power steering ECU assembly.

Scheme 34

The power steering ECU assembly detects steering force using the signal received from the torque sensor, and also monitors the motor circuit for errors.

The torque sensor converts the rotation torque received from the steering wheel into electric signals and sends them to the power steering ECU assembly.

Scheme 35

These DTCs do not indicate a malfunction. The power steering ECU assembly stores these DTCs when it determines that rotation angle sensor initialization and torque sensor zero point calibration have not been performed.

Scheme 36

If the power steering ECU assembly detects a malfunction, the EPS warning light comes on. At this time, the power steering ECU assembly stores a DTC in its memory.

Scheme 37

Connecting terminals TC and CG of the DLC3 causes the ECU to display DTCs by blinking the EPS warning light.

Scheme 38

Assist map writing can be performed after entering Signal Check by connecting the TS and CG terminals of the DLC3 using SST.

Refer to CALIBRATION [04/2013 - ]

Scheme 39

The electronic throttle and the EPS character change by the operation of the drive mode select switch (combination switch assembly).

Scheme 40

Scheme 41

1. CHECK THE PROBLEM SYMPTOMS Check each symptom by checking the suspected areas in the table below. Result Result Proceed to SPORT, SPORT S/S+ mode or NORMAL mode is abnormal. A ECO mode is abnormal. B Result: 2 B GO TO AIR CONDITIONING SYSTEM. Refer to ECO Switch Circuit [04/2013 - ] Result: 1 A See step 2
2. CHECK CAN COMMUNICATION SYSTEM Check for DTCs. Refer to DIAGNOSIS SYSTEM [04/2013 - ] Result Result Proceed to CAN communication system DTCs are not output. A CAN communication system DTCs are output. B Result: 2 B GO TO CAN COMMUNICATION SYSTEM. Refer to HOW TO PROCEED WITH TROUBLESHOOTING [04/2013 - ] Result: 1 A See step 3
3. CHECK HARNESS AND CONNECTOR (DRIVE MODE SELECT SWITCH (COMBINATION SWITCH ASSEMBLY) - BODY GROUND) Turn the engine switch off. Disconnect the K81 drive mode select switch (combination switch assembly) connector. *a Front view of wire harness connector (to Drive mode select switch (combination switch assembly)) Measure the resistance according to the value(s) in the table below. Standard Resistance Tester Connection Condition Specified Condition K81-16 (E) - Body ground Always Below 1 ohms Result Proceed to OK NG Result: 2 NG REPAIR OR REPLACE HARNESS OR CONNECTOR Result: 1 OK See step 4
4. INSPECT DRIVE MODE SELECT SWITCH (COMBINATION SWITCH ASSEMBLY) Inspect drive mode select switch (combination switch assembly). Refer to PROCEDURE - Step 1 OK Drive mode select switch (combination switch assembly) is normal. Result Proceed to OK NG Result: 2 NG REPLACE COMBINATION SWITCH ASSEMBLY. Refer to REMOVAL [04/2013 - ] Result: 1 OK See step 5
5. CHECK HARNESS AND CONNECTOR (DRIVE MODE SELECT SWITCH (COMBINATION SWITCH ASSEMBLY) - ECM) Reconnect the K81 drive mode select switch (combination switch assembly) connector. Disconnect the A76 and A77 ECM connectors. *A w/ Adaptive Variable Suspension System *B w/o Adaptive Variable Suspension System *a Rear view of wire harness connector (to ECM) Measure the resistance according to the value(s) in the table below. Standard Resistance W/ ADAPTIVE VARIABLE SUSPENSION SYSTEM Tester Connection Condition Specified Condition A76-16 (SPSW) - Body ground SPORT mode switch being turned and held Below 50 ohms A76-16 (SPSW) - Body ground SPORT mode switch not turned 10 kohms or higher A77-25 (SPCN) - Body ground NORMAL mode switch being pushed and held Below 50 ohms A77-25 (SPCN) - Body ground NORMAL mode switch not pushed 10 kohms or higher W/O ADAPTIVE VARIABLE SUSPENSION SYSTEM Tester Connection Condition Specified Condition A77-23 (PWR) - Body ground SPORT mode switch being turned and held Below 50 ohms A77-23 (PWR) - Body ground SPORT mode switch not turned 10 kohms or higher A77-25 (SPCN) - Body ground NORMAL mode switch being pushed and held Below 50 ohms A77-25 (SPCN) - Body ground NORMAL mode switch not pushed 10 kohms or higher Result Proceed to OK NG Result: 1 OK REPLACE ECM for 2GR-FSE: Refer to REMOVAL [04/2013 - ] for 4GR-FSE: Refer to REMOVAL [04/2013 - ] Result: 2 NG REPAIR OR REPLACE HARNESS OR CONNECTOR

See also:
• PROCEDURE - Step 2
• DIAGNOSIS SYSTEM [04/2013 - ]
• REMOVAL [04/2013 - ]
• REMOVAL [04/2013 - ]