Lexus RX (RX 350L, RX450h) 2016-2025 Repair Manual: Lost Communication with Combination Switch ECU (B1278)
DESCRIPTION
The main body ECU (multiplex network body ECU) and windshield wiper switch assembly communicate via LIN communication. The main body ECU (multiplex network body ECU) stores this DTC if communication becomes abnormal.
| DTC No. | Detection Item | DTC Detection Condition | Trouble Area | Memory | DTC Output from |
|---|---|---|---|---|---|
| B1278 | Lost Communication with Combination Switch ECU | When the battery voltage is 9.5 V or more, a communication malfunction between the main body ECU (multiplex network body ECU) and windshield wiper switch assembly is detected for 10 seconds or more. |
| ○ | Main body ECU (multiplex network body ECU) |
WIRING DIAGRAM
PROCEDURE
| 1. | CLEAR DTC |
(a) Clear the DTCs.
Click here .gif)
|
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| 2. | CHECK FOR DTC |
(a) Turn the engine switch on (IG).
(b) Check for DTCs.
Click here
| Result | Proceed to |
|---|---|
| DTC B1278 is not output. | A |
| DTC B1278 is output. | B |
| A | .gif) | USE SIMULATION METHOD TO CHECK |
|
| 3. | CHECK HARNESS AND CONNECTOR (MAIN BODY ECU (MULTIPLEX NETWORK BODY ECU) - WINDSHIELD WIPER SWITCH ASSEMBLY) |
(a) Disconnect the J9 main body ECU (multiplex network body ECU) connector.
(b) Disconnect the J31 windshield wiper switch assembly connector.
(c) Measure the resistance according to the value(s) in the table below.
Standard Resistance:
| Tester Connection | Condition | Specified Condition |
|---|---|---|
| J9-8 (LIN3) - J31-7 (MPX1) | Always | Below 1 Ω |
| J9-8 (LIN3) or J31-7 (MPX1) - Body ground | Always | 10 kΩ or higher |
| NG | | REPAIR OR REPLACE HARNESS OR CONNECTOR |
|
| 4. | CHECK HARNESS AND CONNECTOR (FRONT WIPER MOTOR AND LINK ASSEMBLY - POWER SOURCE) |
(a) Measure the voltage according to the value(s) in the table below.
Standard Voltage:
| Tester Connection | Condition | Specified Condition |
|---|---|---|
| J31-10 (+B2) - Body ground | Engine switch off | Below 1 V |
| Engine switch on (IG) | 11 to 14 V | |
| J31-6 (+B) - Body ground | Engine switch off | Below 1 V |
| Engine switch on (IG) | 11 to 14 V |
| NG | | REPAIR OR REPLACE HARNESS OR CONNECTOR |
|
| 5. | CHECK HARNESS AND CONNECTOR (WINDSHIELD WIPER SWITCH ASSEMBLY - BODY GROUND) |
(a) Disconnect the J33 windshield wiper switch assembly connector.
(b) Measure the resistance according to the value(s) in the table below.
Standard Resistance:
| Tester Connection | Condition | Specified Condition |
|---|---|---|
| J31-8 (E) - Body ground | Always | Below 1 Ω |
| J33-4 (EW) - Body ground | Always | Below 1 Ω |
| NG | | REPAIR OR REPLACE HARNESS OR CONNECTOR |
|
| 6. | REPLACE WINDSHIELD WIPER SWITCH ASSEMBLY |
(a) Replace the windshield wiper switch assembly with a new or known good one.
Click here
(b) Turn the engine switch on (IG).
(c) Check for DTCs.
Click here
| Result | Proceed to |
|---|---|
| DTC B1278 is not output. | A |
| DTC B1278 is output. | B |
| A | | END |
| B | | REPLACE MAIN BODY ECU (MULTIPLEX NETWORK BODY ECU) |
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Lexus RX (RX 350L, RX450h) 2016-{YEAR} Repair Manual
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