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Inspection Procedure 4: Vehicle power does not turn ON. (Not possible with power supply mode ON only)
 
 
cautionBefore replacing the ECU, ensure that the power supply circuit, the ground circuit and the communication circuit are normal.
 
 
 
 
TECHNICAL DESCRIPTION (COMMENT)
If the vehicle power does not turn ON (not possible with power supply mode ON only), the possible cause may be that the OSS-ECU cannot output the IG1 signal, or that the IG1 internal relay of ETACS-ECU does not turn ON. Therefore, OSS-ECU or ETACS-ECU may have a problem.
 
 
TROUBLESHOOTING HINTS
  • Malfunction of OSS-ECU
  • Malfunction of ETACS-ECU
  • Damaged harness wires and connectors
 
 
DIAGNOSIS
STEP 1. 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 2.
 
STEP 2. Voltage measurement at ETACS-ECU connector (IG1 terminal)
(1) With the ETACS-ECU connector kept connected, measure by backprobing.
(2) Using the scan tool MB991958, set the forced power supply output to "IG-ON" (Refer to forced power supply output procedure ).
(3) Measure the voltage between the ETACS-ECU connector (IG1 terminal) and body ground.
OK: Battery voltage
Is the check result normal?
Go to Step 3.
Replace the OSS-ECU and register the VIN (Refer to ).
 
STEP 3. Check of the troubles
Check that the vehicle power (power supply mode ON) 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 ).