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DTC P104B: 12 V control power supply voltage too low
 
 
 
 
TROUBLE JUDGMENT
Check Condition
  • The power supply mode of the electric motor switch is ON.
 
 
PROBABLE CAUSES
  • The 12V starter battery is flat (The electric motor switch remains at ON or ACC for long period, or not used for long period)
  • Malfunction of the 12V starter battery
  • Loose 12V starter battery terminals
  • ECU control power supply circuit system fails
  • Malfunction of the on board charger/DC-DC converter
  • Malfunction of the power drive unit [generator control unit (GCU)]
  • Malfunction of the PHEV-ECU
noteIf the vehicle is left with the power supply mode of the electric motor switch at ACC or ON or the vehicle is not used for a long time, the diagnostic trouble code may be set.

 
 
DIAGNOSIS
Required Special Tools
  • MB991223: Wiring harness set
  • MB992006: Extra fine probe
STEP 1. Using scan tool (M.U.T.-IIISE), check whether the other DTC is set.
Check whether the REMCU set a DTC P1035 which is related to the 12 V control power supply voltage too low.
Is the DTC set?
Go to Step 3.
Go to Step 2.
 
STEP 2. Measure the resistance in the IGCT line between the power drive unit connector and the IGCT control relay connector.
(1) Disconnect the power drive unit connector.
(2) Remove the IGCT control relay.
(3) Measure the resistance between the power drive unit connector (IGCT terminal) and the relay box 3 (IGCT control relay connector).
OK: Continuity exists (2 Ω or less)
Is the check result normal?
Replace the power drive unit (Refer to ).
Replace the wiring harness (IGCT line).
 
STEP 3. 12V starter battery check
Refer to GROUP 54A - Battery Test .
Is the check result normal?
Go to Step 4.
Replace the 12V starter battery (Refer to GROUP 54A - 12V starter battery Removal and Installation ).
 
STEP 4. Using scan tool (M.U.T.-IIISE), check whether the other DTC is set.
Check whether the PHEV-ECU sets a diagnostic trouble code which is related to the on board charger/DC-DC converter (Refer to ).
Is the DTC set?
Diagnose the system according to the set diagnostic trouble code.
Go to Step 5.
 
STEP 5. IGCT relay check
Refer to .
Is the check result normal?
Go to Step 6.
Replace the IGCT control relay.
 
STEP 6. Measure the resistance in the 12V starter battery line between the 12V starter battery positive terminal and the IGCT control relay connector.
(1) Disconnect the 12V starter battery positive terminal.
(2) Remove the IGCT control relay.
(3) Measure the resistance between the 12V starter battery positive terminal and the relay box 3 (IGCT control relay connector).
OK: Continuity exists (2 Ω or less)
Is the check result normal?
Go to Step 7.
Replace the wiring harness (12V starter battery line).
 
STEP 7. Measure the resistance in the CTLM line between the PHEV-ECU connector and the IGCT control relay connector.
(1) Disconnect the PHEV-ECU connector.
(2) Remove the IGCT control relay.
(3) Measure the resistance between the PHEV-ECU connector (CTLM terminal) and the relay box 3 (IGCT control relay connector).
OK: Continuity exists (2 Ω or less)
Is the check result normal?
Replace the PHEV-ECU (Refer to GROUP 54Da - PHEV-ECU ).
Replace the wiring harness (CTLM line).