Diagnosis Item 29: Diagnose when the M.U.T.-III cannot receive the data sent by engine-ECU.
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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.
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FUNCTION
The diagnostic result demonstrates that "the M.U.T.-III cannot receive the sent data from the engine-ECU" when the M.U.T.-III checks the periodically sent data from each ECU and cannot receive the engine-ECU data only.
TROUBLE JUDGEMENT CONDITIONS
M.U.T.-III judges the trouble when the periodically sent data from engine-ECU cannot be received.
PROBABLE CAUSES
- Damaged harness wires and connectors
- Power supply circuit malfunction of the engine-ECU
- Malfunction of the engine-ECU
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STEP 1. Connector check: joint connector (CAN1) <Vehicles without ACC> or joint connector (CAN2) <Vehicles with ACC> and engine-ECU connector
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The strand end of the twist wire should be within 10 cm from the connector.
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When checking the joint connector, ensure that its wiring harness side and its short pins are not damaged.
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Q.
Is the check result normal?
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 Go to Step 2.
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 Repair the defective connector. Replace the joint connector as necessary.
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STEP 2. Resistance measurement at joint connector (CAN1) <Vehicles without ACC> or joint connector (CAN2) <Vehicles with ACC> and engine-ECU connector.
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A digital multimeter should be used.
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The test wiring harness should be used.
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(1)Disconnect the joint connector (CAN1) <vehicles without ACC> or joint connector (CAN2) <vehicles with ACC> and the engine-ECU connector, and measure at the wiring harness side.
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(2)Turn the ignition switch to the LOCK (OFF) position.
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(3)
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When measuring the resistance, disconnect the negative battery terminal.
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Ensure that the negative battery terminal is disconnected.
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(4)Continuity between joint connector (CAN1) terminal No.8 and engine-ECU connector terminal No.90 <4B1, 4J1, 6B3> or No.108 <4N1> <Vehicles without ACC>
OK: Continuity (2 Ω or less)
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(5)Continuity between joint connector (CAN1) terminal No.17 and engine-ECU connector terminal No.91 <4B1, 4J1, 6B3> or No.109 <4N1> <Vehicles without ACC>
OK: Continuity (2 Ω or less)
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(6)Continuity between joint connector (CAN2) terminal No.10 and engine-ECU connector terminal No.90 <4B1, 4J1, 6B3> or No.108 <4N1> <Vehicles with ACC>
OK: Continuity (2 Ω or less)
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(7)Continuity between joint connector (CAN2) terminal No.21 and engine-ECU connector terminal No.91 <4B1, 4J1, 6B3> or No.109 <4N1> <Vehicles with ACC>
OK: Continuity (2 Ω or less)
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Strictly observe the specified wiring harness repair procedure.
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Q.
Is the check result normal?
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<All the resistances measure 2 Ω or less> Go to Step 3.
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NO : <Either or all of the resistances measure more than 2 Ω> Repair the wiring harness between joint connector (CAN1) <Vehicles without ACC> or joint connector (CAN2) <Vehicles with ACC> and the engine-ECU.
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STEP 3. Resistance measurement at engine-ECU connector.
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A digital multimeter should be used.
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(1)Remove the engine-ECU, and measure at the equipment side.
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(2)Resistance between engine-ECU connector terminal Nos.90 and 91 <4B1, 4J1, 6B3>
OK: 120 ± 20 Ω
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(3)Resistance between engine-ECU connector terminal Nos.108 and 109 <4N1>
OK: 120 ± 20 Ω
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Strictly observe the specified wiring harness repair procedure.
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Q.
Is the check result normal?
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<Within 120 ± 20 Ω> Power supply to the engine-ECU may be suspected. Diagnose the fuel system. (Refer to GROUP 13A - Diagnosis Code Chart <4B1>, GROUP 13B - Diagnosis Code Chart <6B3>, GROUP 13D - Diagnosis Code Chart <4N1>, GROUP 13E - Diagnosis Code Chart <4J1>)
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<Not within 120 ± 20 Ω> Replace the engine-ECU.
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