DESCRIPTION
A backup boost converter is built into the engine stop and start ECU. The backup boost converter helps maintain the power source voltage when the engine is restarted by stop and start control.
This prevents various functions such as the audio and visual system from malfunctioning if the power source voltage drops due to the battery voltage dropping when the engine is restarted by stop and start control.
If any DTCs are output, troubleshoot the DTCs first.
Tech Tips
A relay function and fuse function are provided in the backup boost converter.
If there is a malfunction in any of the electrical system circuits connected to the backup boost converter, the fuse and relay functions shut off the malfunctioning circuit to protect other circuits (remains shut off until next trip).
When the electrical system circuit is shut off, power to the circuit is cut off, causing any systems connected to the circuit to be disabled.
The fuse function is reset* when the engine switch is turned off. If the malfunction still exists in the electrical system circuit that has been shut off by the relay function, it will be shut off again by the relay and fuse functions the next time the engine switch is turned on (IG).
*: A semiconductor fuse self resets according to electric signal.
The backup boost converter supplies power to:
Tire pressure warning system
Power steering system
Lighting system
Telematics system
Navigation system
Audio and visual system
Blind spot monitor system
Headup display system
Lexus safety system +
CAN communication system
Lexus parking assist-sensor system
Panoramic view monitor system
Vehicle stability control system
Meter / gauge system
The eco run vehicle converter assembly (external backup boost converter) supplies power to:
Navigation system
Audio and visual system
WIRING DIAGRAM
CAUTION / NOTICE / HINT
Note
Before replacing the engine stop and start ECU, read the number of starter operations and total number of engine starts and write it into a new engine stop and start ECU.
After replacing the engine stop and start ECU or air conditioning amplifier assembly, reset and perform learning of the air conditioning information in the engine stop and start ECU.
After replacing the engine stop and start ECU, airbag sensor assembly*1 or yaw rate and acceleration sensor*2, clear and calibrate the deceleration sensor zero point in the engine stop and start ECU.
*1: for Optitron Meter Type
*2: for TFT Meter Type
Inspect the fuses for circuits related to this system before performing the following procedure.
PROCEDURE
CHECK PROBLEM SYMPTOMS
Determine the trouble area by referring to the table below.
Effect on Vehicle | Trouble Area/Cause | Fail-safe | DTC Output | Stop and start cancel indicator light | Symptom | Proceed to |
---|---|---|---|---|---|---|
When the engine is restarted by stop and start control:
The following symptoms may occur |
Backup boost converter internal malfunction
|
Stop and start control prohibited | P323B | Blinks | Systems stop operating during engine restart as the backup boost converter output voltage cannot be boosted | A |
Battery voltage drop | ||||||
Systems on the converter output side do not operate
B41 terminal: All of the following will not operate
B42 terminal: All of the following will not operate
B43 terminal: All of the following will not operate
IG41 terminal: All of the following will not operate |
Overcurrent applied to an output terminal (output terminal relay circuit is shutoff) | Stop and start control is prohibited (Connected ECUs or sensors may detect power source malfunction DTCs) |
B22C0 | Blinks | Systems do not operate as power supply from the converter is cut off | A |
Systems do not operate (Due to converter input side malfunction)
IG1 terminal: All of the following will not operate
IG2 terminal: All of the following will not operate
ACC terminal: All of the following will not operate |
Converter input circuit malfunction
|
Stop and start control prohibited | - | Does not blink (Blinks when communication error DTCs are stored) | Systems do not operate as power supply from the converter is cut off | B |
Systems on the converter output side do not operate (varies depending on the malfunctioning relay circuit the converter detected)
AC41 terminal:
AC42 terminal:
IG11 terminal:
IG12 terminal:
IG13 terminal:
IG31 terminal:
B12 terminal:
IL41 terminal: |
Malfunction in circuits the converter supplies power to (between the converter and ECUs or sensors)
|
Related systems do not operate as the relay circuit in the converter is turned off | - | Does not blink (Blinks when communication error DTCs are stored) | Systems do not operate as power supply from the converter is cut off | B |
All of the following systems do not operate: |
|
Stop and start control prohibited | P0617 | Does not blink (Due to disabled meter/gauge system) | All systems that the converter supplies power to do not operate (see circuit diagram) | A |
P323B | ||||||
The audio does not operate (until the engine switch is turned off) |
Excessive audio volume Data List item "State of BBC" displays "BBC Overcurrent" while the circuit is protected |
The relay circuit in the converter is turned off to cut off power supply to the audio and visual system (Returns to normal when the engine switch is turned off) | - | Does not blink | If overcurrent is detected in the audio and visual system, system operation is disabled while the engine switch is on (IG) (Returns to normal when the engine switch is turned off) |
C |
Tech Tips Varies depending on the number of times an open occurs in the +B circuit |
Converter circuit malfunction
|
- | - | Does not blink | The converter cannot shut off the power source when the engine switch is turned off | B |
Engine switch does not turn on (ACC) (short between ACC and +B) Engine switch does not turn off (short between IG1 or IG2 and +B) |
Engine stop and start ECU power source circuit malfunction
|
- | - | Does not blink |
|
B |
Result | ||||
---|---|---|---|---|
|
A |
GO TO DIAGNOSTIC TROUBLE CODE CHART Click here |
C |
CHECK AUDIO AND VISUAL SYSTEM Click here |
B |
CHECK ENGINE STOP AND START ECU (POWER SOURCE CIRCUIT)
*a | Front view of wire harness connector (to Engine Stop and Start ECU) |
Disconnect the engine stop and start ECU connector.
Measure the voltage according to the value(s) in the table below.
Standard Voltage | |||||||||
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|
Turn the engine switch on (ACC).
Measure the voltage according to the value(s) in the table below.
Standard Voltage | ||||||
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Turn the engine switch on (IG).
Measure the voltage according to the value(s) in the table below.
Standard Voltage | |||||||||
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Turn the headlight dimmer switch (light control switch) to the tail or head position.
Measure the voltage according to the value(s) in the table below.
Standard Voltage | ||||||
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|
Turn the engine switch off.
Measure the voltage according to the value(s) in the table below.
Standard Voltage | ||||||||||||
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Result | |||
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NG |
REPAIR OR REPLACE HARNESS OR CONNECTOR |
OK |
CHECK HARNESS AND CONNECTOR (ENGINE STOP AND START ECU - EACH ECU OR SENSOR)
Disconnect the connector from the corresponding system ECU/sensor.
Measure the resistance according to the value(s) in the table below.
Standard Resistance | ||||||||||||||||||||||||||||||
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Result | |||
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NG |
REPAIR OR REPLACE HARNESS OR CONNECTOR |
OK |
CHECK ENGINE STOP AND START ECU (EACH ECU OR SENSOR POWER SOURCE CIRCUIT)
Disconnect the connector from the corresponding system ECU/sensor.
Measure the voltage according to the value(s) in the table below.
Tech Tips
Measure the voltage at the corresponding terminals.
Standard Voltage | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
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|
Turn the engine switch on (ACC).
Measure the voltage according to the value(s) in the table below.
Tech Tips
Measure the voltage at the corresponding terminals.
Standard Voltage | ||||||||||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
Turn the engine switch on (IG).
Measure the voltage according to the value(s) in the table below.
Tech Tips
Measure the voltage at the corresponding terminals.
Standard Voltage | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
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|
Turn the headlight dimmer switch (light control switch) to the tail or head position.
Measure the voltage according to the value(s) in the table below.
Tech Tips
Measure the voltage at the corresponding terminals.
Standard Voltage | |||||||||
---|---|---|---|---|---|---|---|---|---|
|
*1: for Tire Pressure Warning ECU and Receiver Integrated with Electrical Key Receiver
*2: for Tire Pressure Warning ECU and Receiver (Stand Alone)
*3: w/ Blind Spot Monitor System
*4: w/ Instrument Panel Ambient Illumination Light
*5: w/ Navigation System or Audio and Visual System (for 12.3 Inch Display)
*6: w/ Audio and Visual System (for 8 Inch Display)
*7: w/ Telematics System
*8: w/ Panoramic View Monitor System
*9: w/ Headup Display System
*10: w/ Lexus Safety System +
*11: w/ Lexus Parking Assist-sensor System
*12: w/ TFT Meter Display
Result | |||
---|---|---|---|
|
OK |
CHECK POWER SOURCE CIRCUIT (POWER SOURCE CIRCUIT OF RELATED SYSTEM) |
NG |
REPLACE ENGINE STOP AND START ECU Click here |
CHECK AUDIO AND VISUAL SYSTEM
Turn the engine switch off and wait for 1 minute.
Turn the engine switch on.
Lower the audio volume.
Check if the audio and visual system operates normally.
OK |
---|
Audio and visual system operates normally. |
Result | |||
---|---|---|---|
|
OK |
END |
NG |
CHECK HARNESS AND CONNECTOR (ENGINE STOP AND START ECU - RADIO RECEIVER ASSEMBLY)
Disconnect the J52*1 or J50*2 radio and display receiver assembly connector.
Disconnect the J46 engine stop and start ECU connector.
Measure the resistance according to the value(s) in the table below.
Standard Resistance | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
|
*1: for Audio and Visual System (for 8 Inch Display)
*2: for Navigation System or Audio and Visual System (for 12.3 Inch Display)
Result | ||||||||
---|---|---|---|---|---|---|---|---|
|
A |
GO TO AUDIO AND VISUAL SYSTEM for 8 Inch Display: Click here for 12.3 Inch Display: Click here |
B |
GO TO NAVIGATION SYSTEM Click here |
C |
REPAIR OR REPLACE HARNESS OR CONNECTOR |