Diagnosis Item 28: Diagnose when the M.U.T.-III cannot receive the data sent by A/C-ECU.

caution When servicing a CAN bus line, earth yourself by touching a metal object such as an unpainted water pipe. If you fail to do, a component connected to the CAN bus line may be broken.


The diagnostic result demonstrates that "the M.U.T.-III cannot receive the sent data from the A/C-ECU" when the M.U.T.-III checks the periodically sent data from each ECU and cannot receive the A/C-ECU data only.


M.U.T.-III judges the trouble when the periodically sent data from A/C-ECU cannot be received.



STEP 1. Connector check: joint connector (CAN5) and A/C-ECU connector

caution The strand end of the twist wire should be within 10 cm from the connector. For details refer to .
When checking the joint connector, ensure that its wiring harness side and its short pins are not damaged.

Q. Is the check result normal?

Go to Step 2.
Repair the defective connector. Replace the joint connector as necessary.

STEP 2. Resistance measurement at joint connector (CAN5) and A/C-ECU connector.

caution A digital multimeter should be used. For details refer to .
caution The test wiring harness should be used. For details refer to .
(1)Disconnect joint connector (CAN5) and the A/C-ECU connector, and measure at the wiring harness side.
(2)Turn the ignition switch to the LOCK (OFF) position.
caution When measuring the resistance, disconnect the negative battery terminal. For details refer to .
Ensure that the negative battery terminal is disconnected.
(4)Continuity between joint connector (CAN5) terminal No.6 and A/C-ECU connector terminal No.32
OK: Continuity (2 Ω or less)
(5)Continuity between joint connector (CAN5) terminal No.17 and A/C-ECU connector terminal No.31
OK: Continuity (2 Ω or less)
caution Strictly observe the specified wiring harness repair procedure. For details refer to .

Q. Is the check result normal?

<All the resistances measure 2 Ω or less> Power supply to the A/C-ECU may be suspected. Diagnose the A/C. Refer to GROUP 55 - Troubleshooting .
NO : <Either or all of the resistances measure more than 2 Ω> Repair the wiring harness between joint connector (CAN5) and the A/C-ECU connector.