Toyota CH-R Service Manual: Communication Malfunction between ECUs Connected by LIN (B2785)

Toyota CH-R Service Manual / Networking / Lin Communication System / Communication Malfunction between ECUs Connected by LIN (B2785)

DESCRIPTION

If the certification ECU (smart key ECU assembly) detects a communication error with an ECU connected to the certification bus lines for 7 seconds or more, DTC B2785 will be stored.

DTC No.	Detection Item	DTC Detection Condition	Trouble Area
B2785	Communication Malfunction between ECUs Connected by LIN	Any of the following conditions is met: Errors in LIN communication between ECUs. Open in communication lines. Short in communication lines. The certification ECU (smart key ECU assembly) detects a communication error with an ECU connected to the certification bus lines for 7 seconds or more.	Certification ECU (smart key ECU assembly) Steering lock ECU (steering lock actuator or upper bracket assembly) ID code box (immobiliser code ECU) Wire harness or connector AM2 fuse STRG LOCK fuse ECU-B NO. 1 fuse

DTC Detection Conditions

		Vehicle Condition
		Pattern 1	Pattern 2	Pattern 3	Pattern 4
Diagnosis Condition	-	○	○	○	○
Malfunction Status	Errors in LIN communication between ECUs	○	-	-	-
	Open in communication lines	-	○	-	-
	Short in communication lines	-	-	○	-
	The certification ECU (smart key ECU assembly) detects a communication error with an ECU connected to the certification bus lines	-	-	-	○
Detection Time		-	-	-	7 seconds or more
Number of Trips		1 trip	1 trip	1 trip	1 trip

HINT:

DTC will be output when conditions for either of the patterns in the table above are met.

WIRING DIAGRAM

CAUTION / NOTICE / HINT

NOTICE:

Inspect the fuses for circuits related to this system before performing the following procedure.
Before performing the inspection, check that DTC B2786, B2789 or B278C is not output.
Click here
When using the Techstream with the ignition switch off, connect the Techstream to the DLC3 and turn a courtesy light switch on and off at intervals of 1.5 seconds or less until communication between the Techstream and the vehicle begins. Then select the vehicle type under manual mode and enter the following menus: Body Electrical / Smart Key. While using the Techstream, periodically turn a courtesy light switch on and off at intervals of 1.5 seconds or less to maintain communication between the Techstream and the vehicle.
If the certification ECU (smart key ECU assembly), ID code box (immobiliser code ECU) and steering lock ECU (steering lock actuator or upper bracket assembly) is replaced, refer to Registration.
Click here

PROCEDURE

1.	CHECK HARNESS AND CONNECTOR (CERTIFICATION ECU (SMART KEY ECU ASSEMBLY) - EACH ECU)

(a) Disconnect the F1 certification ECU (smart key ECU assembly) connector.

(b) Disconnect the F78 steering lock ECU (steering lock actuator or upper bracket assembly) connector.

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

NOTICE:

Make sure that each ECU is in sleep mode before performing the inspection. To enter sleep mode, turn the ignition switch from ON to off and wait for 180 seconds or more without operating any switches.

Standard Resistance:

Tester Connection	Switch Condition	Specified Condition
F1-13 (LIN) - F21-2 (LIN1)	Ignition switch off	Below 1 Ω
F1-13 (LIN) - F78-5 (LIN)	Ignition switch off	Below 1 Ω
F1-13 (LIN), F78-5 (LIN) or F21-2 (LIN1) - Body ground	Ignition switch off	10 kΩ or higher

REPAIR OR REPLACE HARNESS OR CONNECTOR

2.	CHECK FOR DTC (STEERING LOCK ECU (STEERING LOCK ACTUATOR OR UPR BRACKET ASSEMBLY))

(a) Reconnect the F1 certification ECU (smart key ECU assembly) connector.

(b) Reconnect the F21 ID code box (immobiliser code ECU) connector.

Click here

Body Electrical > Smart Key > Clear DTCs

(d) Recheck for DTCs.

Body Electrical > Smart Key > Trouble Codes

Result	Proceed to
DTC B2785 is output	A
DTC B2785 is not output	B

REPLACE STEERING LOCK ECU (STEERING LOCK ACTUATOR OR UPPER BRACKET ASSEMBLY)

3.	CHECK FOR DTC (ID CODE BOX (IMMOBILISER CODE ECU))

(a) Reconnect the F78 steering lock ECU (steering lock actuator or upper bracket assembly) connector.

(b) Disconnect the F21 ID code box (immobiliser code ECU) connector.

Click here

Body Electrical > Smart Key > Clear DTCs

(d) Recheck for DTCs.

Body Electrical > Smart Key > Trouble Codes

Result	Proceed to
DTC B2785 is output	A
DTC B2785 is not output	B

REPLACE CERTIFICATION ECU (SMART KEY ECU ASSEMBLY)

REPLACE ID CODE BOX (IMMOBILISER CODE ECU)

No Response from ID BOX (B2789)

DESCRIPTION This DTC is stored when LIN communication between the certification ECU (smart key ECU assembly) and ID code box (immobiliser code ECU) stops for 10 seconds or more. DTC N ...

P/W Master Switch Communication Stop (B1206)

DESCRIPTION This DTC is stored when LIN communication between the multiplex network master switch assembly and main body ECU (multiplex network body ECU) stops for 10 seconds or more. ...

Other materials:

Toyota CH-R Service Manual > Door Control Transmitter(w/ Smart Key System): Components
COMPONENTS ILLUSTRATION *1 TRANSMITTER BATTERY *2 MECHANICAL KEY *3 TRANSMITTER HOUSING COVER *4 TRANSMITTER HOUSING CASE *5 SMART KEY DOOR CONTROL TRANSMITTER HOUSING SET ...

Toyota CH-R Service Manual > Pre-collision System: Diagnostic Trouble Code Chart
DIAGNOSTIC TROUBLE CODE CHART Pre-collision System DTC No. Detection Item Link C1A02 Vehicle Information Not Obtained C1A10 Front Radar Sensor C1A11 Front ...

Toyota CH-R Service Manual: Communication Malfunction between ECUs Connected by LIN (B2785)

No Response from ID BOX (B2789)

P/W Master Switch Communication Stop (B1206)

Other materials:

Toyota C-HR (AX20) 2023-2025 Owner's Manual

Toyota CH-R Owners Manual

Toyota CH-R Service Manual