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Inspection procedure 1: Communication with ECM only is not possible
 
 
 
 
CIRCUIT OPERATION
  • 12V starter battery voltage is applied to the data link connector.
  • The data link connector is grounded to the vehicle body.
 
 
COMMENT
  • When the communication between scan tool (M.U.T.-IIISE) and ECM is impossible, it can be suspected that the CAN bus line, power supply circuit of the data link connector, and/or grounding circuit are defective.
  • Communication cannot be achieved either, if a wrong vehicle type is selected on scan tool (M.U.T.-IIISE).
 
 
TROUBLESHOOTING HINTS (The most likely causes for this case:)
  • 12V starter battery failed.
  • Open or shorted data link connector circuit, harness damage or connector damage.
  • CAN communication failed.
  • Scan tool (M.U.T.-IIISE) failed.
  • ECM failed.

 
 
DIAGNOSIS
STEP 1. Check the vehicle communication interface-lite (V.C.I.-Lite) MB992744 operations.
cautionTo prevent damage to scan tool (M.U.T.-IIISE), always turn off the power supply mode of the electric motor switch before connecting or disconnecting scan tool (M.U.T.-IIISE).
(1) Connect scan tool (M.U.T.-IIISE). Refer to HOW TO CONNECT THE SCAN TOOL (M.U.T.-IIISE) .
(2) The indicator lamp of the V.C.I.-Lite illuminates in green.
Is the indicator lamp of the V.C.I.-Lite illuminates in green?
Go to Step 10.
Go to Step 2.
 
STEP 2. Check the 12V starter battery.
Refer to GROUP 54A, 12V Starter Battery - On-vehicle Service - 12V Starter Battery Test .
Are there any abnormalities?
Replace the 12V starter battery. Then confirm that the malfunction symptom is eliminated.
Go to Step 3.
 
STEP 3. Measure the power supply voltage at data link connector harness side connector.
Measure voltage between terminal MUT and ground.
  • Voltage should be 12V starter battery positive voltage.
Is 12V starter battery positive voltage (approximately 12 volts) present?
Go to Step 6.
Go to Step 4.
 
STEP 4. Check of short to ground and open circuit in MUT line between ETACS-ECU connector and data link connector.
Is the harness wire in good condition?
Go to Step 5.
Repair the connector(s) or wiring harness. Then confirm that the malfunction symptom is eliminated.
 
STEP 5. Check of short to ground and open circuit in +B1 line between 12V starter battery and ETACS-ECU connector.
Is the harness wire in good condition?
Check fuse in the ETACS-ECU, and replace as required. If the fuse is in good condition, replace the ETACS-ECU. Then confirm that the malfunction symptom is eliminated.
Repair the connector(s) or wiring harness. Then confirm that the malfunction symptom is eliminated.
 
STEP 6. Check the continuity at data link connector harness side connector.
Check for the continuity between terminal ground line and ground.
  • Continuity (2 ohms or less)
Does continuity exist?
Go to Step 7.
Repair or replace the connector(s), or check and repair the harness of open circuit, and damage in ground line between data link connector and body ground. Then confirm that the malfunction symptom is eliminated.
 
STEP 7. Check the continuity at ETACS-ECU connectors.
(1) Disconnect the connectors and measure at the ETACS-ECU side.
(2) Check for the continuity between terminal +B1 and terminal MUT.
  • Continuity
Does continuity exist?
Go to Step 8.
Check fuse in the ETACS-ECU, and replace as required. If the fuse is in good condition, replace the ETACS-ECU. Then confirm that the malfunction symptom is eliminated.
 
STEP 8. Check of harness damage in +B1 line between 12V starter battery and ETACS-ECU connector.
Is the harness wire in good condition?
Go to Step 9.
Repair the connector(s) or wiring harness. Then confirm that the malfunction symptom is eliminated.
 
STEP 9. Check of harness damage in MUT line between ETACS-ECU and data link connector.
Is the harness wire in good condition?
Refer to the M.U.T.-III SE User's Manual.
Repair the connector(s) or wiring harness. Then confirm that the malfunction symptom is eliminated.
 
STEP 10. Using scan tool (M.U.T.-IIISE), diagnose CAN bus line.
(1) Turn on the power supply mode of the electric motor switch.
(2) Diagnose CAN bus line.
(3) Turn off the power supply mode of the electric motor switch.
Is the CAN bus line normal?
Refer to Inspection Procedure - Power Supply System and OSS-ECU (IG1) System .
Repair the CAN bus line. Refer to GROUP 54C, Diagnosis - CAN Bus Diagnostics Table . Then confirm that the malfunction symptom is eliminated.