U1121

NETWORKING: CAN COMMUNICATION SYSTEM: U1121: Lost Communication with Driver Monitor ECU
U1121 - Lost Communication with Driver Monitor ECU

DESCRIPTION





HINT
The diagnosis procedure is for when DTC U1121 is output by the driver support ECU (Techstream display: Pre-collision2).

WIRING DIAGRAM





INSPECTION PROCEDURE

NOTICE:
* Turn the power switch off before measuring the resistances between CAN bus main wires and between CAN bus branch wires.
* Turn the power switch off before inspecting CAN bus wires for a ground short.
* After the power switch is turned off, check that the key reminder warning system and light reminder warning system are not operating.
* Before measuring the resistance, leave the vehicle as is for at least 1 minute and do not operate the power switch, any other switches or the doors. If any doors need to be opened in order to check connectors, open the doors and leave them open.

HINT
* Operating the power switch, any other switches or a door triggers related ECU and sensor communication on the CAN. This communication will cause the resistance value to change.
* Even after DTCs are cleared, if a DTC is stored again after driving the vehicle for a while, the malfunction may be occurring due to vibration of the vehicle. In such a case, wiggling the ECUs or wire harness while performing the inspection below may help determine the cause of the malfunction.

PROCEDURE

1. RECONFIRM DTC OUTPUT

(a) Reconfirm DTCs.

HINT
If parking assist bus DTC U1002 is output from the driver support ECU (Techstream display/pre-collision2), troubleshoot for U1002 and check for malfunctions in the driving support main bus circuit.

Result:





B -- GO TO CIRCUITS INDICATED BY OUTPUT DTCS U1002
A -- Continue to next step.

2. CHECK CAN BUS WIRE FOR DISCONNECTION (DRIVER MONITOR ECU BRANCH WIRE)

(a) Disconnect the driver monitor ECU connector.





Text in Illustration





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

Standard Resistance:





NG -- REPAIR OR REPLACE CAN BUS BRANCH WIRE OR CONNECTOR (DRIVER MONITOR ECU)
OK -- Continue to next step.

3. CHECK HARNESS AND CONNECTOR (POWER SOURCE CIRCUIT)

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





Standard Resistance:





Text in Illustration





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

Standard Voltage:





NG -- REPAIR OR REPLACE HARNESS OR CONNECTOR (POWER SOURCE CIRCUIT)

OK -- REPLACE DRIVER MONITOR ECU Removal