Lexus RX (RX 350L, RX450h) 2016-2022 Repair Manual: MOST Communication Malfunction (B15D0)

DESCRIPTION

Navigation system components communicate with each other via MOST communication.

If a line short or short to ground occurs in a MOST communication line, communication will not be possible and the navigation system will not operate normally.

After the engine switch is turned on (ACC), if the MOST communication network cannot be established and MOST communication is determined to not be possible, this DTC will be stored.

HINT:

Electrical noise may cause communication malfunctions between devices in the MOST network.

DTC No.

Detection Item

DTC Detection Condition

Trouble Area

B15D0

MOST Communication Malfunction

MOST network cannot be established.

  • Stereo component amplifier assembly
  • Radio receiver assembly
  • Harness or connector

WIRING DIAGRAM

CHECK POINT

  • Before proceeding with the following procedure, start diagnostic mode, enter the "MOST Line Check" screen and check the results.
  • The following MOST line check result pattern table can be used to quickly identify trouble areas and inspection procedures.
MOST Network Outline MOST Line Check Result Pattern

Pattern

Device Name

Result

Trouble Area

Inspection

1

DCU

OK

a, c

Inspect MOST communication line between "DCU" and "AMP"

AMP

OK

2

DCU

OK

b, c

Inspect wake up communication line between "DCU" and "AMP"

AMP

NCON

CAUTION / NOTICE / HINT

NOTICE:

Depending on the parts that are replaced during vehicle inspection or maintenance, performing initialization, registration or calibration may be needed. Refer to Precaution for Navigation System.

Click here

PROCEDURE

1.

CHECK DTC

(a) Check for DTCs.

Body Electrical > Navigation System > Trouble Codes

Result

Proceed to

DTC B15C3 and B15D3 are not output

A

DTC B15C3 is output

B

DTC B15D3 is output

C

HINT:

  • If a short occurs in a speaker circuit, the sound output from the speakers will become very low or will stop and DTC B15C3 will be stored.

    In this case, if the audio system volume is increased, current in the speaker circuit will increase more than necessary.

    To prevent the current from becoming excessively high, when it increases to a certain amount, operation of the stereo component amplifier assembly will be suspended.

    If operation is suspended, MOST communication will become impossible, the navigation system will not operate normally and DTC B15D0 will be stored.

  • If DTC B15C3 and B15D3 are output at the same time, perform troubleshooting for DTC B15C3 first.
B

GO TO DTC B15C3

C

GO TO B15D3

A

2.

PERFORM MOST LINE CHECK

(a) Enter the "MOST Line Check" screen. Refer to Check DTC (Check Using System Check Mode Screen) in DTC Check / Clear.

Click here

HINT:

"MOST" is displayed on "System Check Mode" screen when the MOST network is malfunctioning.

Result

Proceed to

"OK" is displayed for all items.

A

"NCON" is displayed for "AMP".

B

*a

MOST Network Device Node Position Number

*b

Device Name

*c

Result

B

GO TO STEP 5

A

3.

CHECK HARNESS AND CONNECTOR (RADIO RECEIVER ASSEMBLY - STEREO COMPONENT AMPLIFIER ASSEMBLY)

(a) Disconnect the J122 radio receiver assembly connector.

(b) Disconnect the J123 stereo component amplifier assembly connector.

(c) Measure the resistance according to the value(s) in the table below.

Standard Resistance:

Tester Connection

Condition

Specified Condition

J122-2 (MI+) - J123-5 (MO+)

Always

Below 1 Ω

J122-3 (MI-) - J123-6 (MO-)

Always

Below 1 Ω

J122-4 (SLDI) - J123-7 (SLDO)

Always

Below 1 Ω

J122-5 (MO+) - J123-2 (MI+)

Always

Below 1 Ω

J122-6 (MO-) - J123-3 (MI-)

Always

Below 1 Ω

J122-7 (SLDO) - J123-4 (SLDI)

Always

Below 1 Ω

J122-2 (MI+) or J123-5 (MO+) - Body ground

Always

10 kΩ or higher

J122-3 (MI-) or J123-6 (MO-) - Body ground

Always

10 kΩ or higher

J122-4 (SLDI) or J123-7 (SLDO) - Body ground

Always

10 kΩ or higher

J122-5 (MO+) or J123-2 (MI+) - Body ground

Always

10 kΩ or higher

J122-6 (MO-) or J123-3 (MI-) - Body ground

Always

10 kΩ or higher

J122-7 (SLDO) or J123-4 (SLDI) - Body ground

Always

10 kΩ or higher

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR

OK

4.

REPLACE STEREO COMPONENT AMPLIFIER ASSEMBLY

(a) Replace the stereo component amplifier assembly with a new or known good one.

Click here

(b) Clear the DTCs.

Body Electrical > Navigation System > Clear DTCs

(c) Recheck for DTCs and check that no DTCs are output.

Body Electrical > Navigation System > Trouble Codes

OK:

No DTCs are output.

OK

END

NG

REPLACE RADIO RECEIVER ASSEMBLY

5.

CHECK HARNESS AND CONNECTOR (STEREO COMPONENT AMPLIFIER ASSEMBLY WAKE UP LINE)

(a) Disconnect the J123 stereo component amplifier assembly connector.

(b) Measure the voltage according to the value(s) in the table below.

Standard Voltage:

Tester Connection

Condition

Specified Condition

J123-8 (WUI) - Body ground

Engine switch on (ACC)

4.5 V or higher

OK

REPLACE STEREO COMPONENT AMPLIFIER ASSEMBLY

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR

    Speaker Output Short (B15C3)
    DESCRIPTION This DTC is stored when a malfunction occurs in the speakers. DTC No. Detection Item DTC Detection Condition Trouble Area B15C3 Speaker Output Short A short is detected in ...

    Stereo Component Amplifier Disconnected (B15D3)
    DESCRIPTION The radio receiver assembly and stereo component amplifier assembly are connected via MOST communication lines. When a MOST communication error occurs between the radio receiver assembly a ...

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