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Inspection Procedure 2: Vehicle power does not turn ON. (not possible with both of power supply mode ACC and ON)
 
 
cautionBefore replacing the ECU, ensure that the power supply circuit, the ground circuit and the communication circuit are normal.
 
 
 
 
TECHNICAL DESCRIPTION (COMMENT)
When the vehicle power does not turn ON (not possible with both of power supply mode ACC and ON), the battery, CAN bus line, OSS-ECU, OSS-ECU power supply, or ground circuit may have a problem.
noteOSS-ECU can communicate with the scan tool MB991958 even when the engine switch is in the "OFF" position.
 
 
TROUBLESHOOTING HINTS
  • Malfunction of battery
  • Damaged wiring harness and connectors
  • Malfunction of engine switch (poor connector contact, poor engine switch contact)
  • Malfunction of the CAN bus line
  • Malfunction of OSS-ECU
  • ETACS-ECU malfunction
 
 
DIAGNOSIS
STEP 1. Battery check
Perform the battery test to check the battery status (Refer to GROUP 54A - Battery ).
Is the check result normal?
Go to Step 2.
Replace the battery.
 
STEP 2. Check that the scan tool MB991958 communicates with this system.
Check that the communication with scan tool MB991958 is possible.
noteIf ETACS-ECU is not active, OSS-ECU cannot communicate with the scan tool MB991958.
(1) Perform the ON/OFF operation of any of the door switches for several times, or open any of the doors.
(2) Check that OSS-ECU can communicate with the scan tool MB991958.
Is the check result normal?
Go to Step 3.
Carry out the troubleshooting of "OSS-ECU power supply or ground circuit malfunction" (Refer to ).
 
STEP 3. Using scan tool MB991958, diagnose the CAN bus line.
(1)
cautionTo prevent damage to scan tool (MB991958), always turn the power supply mode of the engine switch to the OFF position before connecting or disconnecting scan tool (MB991958).
Connect scan tool MB991958. Refer to "How to connect scan tool (M.U.T.-III) ."
(2) After performing the forced power supply output (refer to ) "IG-ON".
(3) Diagnose the CAN bus line.
(4) Turn the power supply mode of the engine switch to OFF.
Is the CAN bus line found to be normal?
Go to Step 4.
Repair the CAN bus line (Refer to GROUP 54C - Troubleshooting ).
 
STEP 4. Using scan tool MB991958, read the diagnostic trouble code
(1)
cautionTo prevent damage to scan tool (MB991958), always turn the power supply mode of the engine switch to the OFF position before connecting or disconnecting scan tool (MB991958).
Connect scan tool MB991958. Refer to "How to connect scan tool (M.U.T.-III) ."
(2) After performing the forced power supply output (refer to forced power supply output procedure ) "IG-ON".
(3) Check if the DTC is set to OSS-ECU.
(4) Turn the power supply mode of the engine switch to OFF.
Is the DTC set?
Diagnose the OSS-ECU. Refer to diagnostic trouble code chart .
Go to Step 5.
 
STEP 5. Connector check: Engine switch connector
Is the check result normal?
Go to Step 6.
Repair the damaged connector.
 
STEP 6. Engine switch check
(1) Remove the engine switch (Refer to ).
(2) Check continuity when the engine switch is operated to "Press" or "Release" position.
 
Switch operationTerminal numberNormal conditions
Press1 - 2Continuity exists (2 ohms or less)
8 - 6
Release1 - 2No continuity
8 - 6
Is the engine switch normal?
Go to Step 7.
Replace the engine switch.
 
STEP 7. Check of the troubles
Check that the vehicle power can be turned ON.
Is the check result normal?
Intermittent malfunction is suspected (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunction ).
Carry out the troubleshooting relevant to the input signal of ETACS-ECU. (Refer to GROUP 54A - ETACS .) Then, go to Step 8.
 
STEP 8. Check of the troubles
Check that the vehicle power can be turned ON.
Is the check result normal?
This diagnosis is complete.
Replace the OSS-ECU and register the VIN (Refer to ).