P0A0FKrytyczny
System napędowy EV — usterka izolacji HV
Układ napędowy
Sprawdź szczegóły →P3120
WysokiFault in the Main Relay Control Circuit of the Hybrid Propulsion System. The code indicates an abnormality in the control circuit of the high-voltage system power relay.
OBD-II (EN): Hybrid Propulsion System Main Relay Control Circuit Fault
Code P3120 signals a fault in the control circuit of the main high-voltage system relay – most commonly found in Toyota/Lexus hybrid vehicles. The cause may be a worn SMR relay, damaged wiring, or a problem with the traction battery. Due to the presence of high voltage (200–650V), diagnosis and repair should be carried out by a certified hybrid system technician.
Symptoms
Check Engine light and hybrid system warning illuminated (READY does not engage or turns off). The vehicle may not start or may shut down while driving. Significant loss of drive power, entering limp mode. Possible complete immobilization of the vehicle.
Possible causes
• Damaged high-voltage system main relay (System Main Relay – SMR1/SMR2/SMR3) • Open or short circuit in the HV relay control circuit wiring • Oxidized or loose connectors in the traction battery relay circuit • Fault in the HV battery control module (Battery ECU / HV ECU) • Degradation or damage to the high-voltage battery pack causing incorrect control signals
Affected systems
Układ wysokiego napięcia (HV)Bateria trakcyjnaSystem Main Relay (SMR)Battery ECU / HV ECUUkład napędowy hybrydy
Related codes
P3125Krytyczny
Kod producenta P3125 – usterka układu hamulcowego (ciśnienie/siła hamowania). Kod specyficzny dla pojazdów grupy PSA (Citroën/Peugeot), wskazujący nieprawidłowości w działaniu układu hamulcowego.
Układ napędowy
Sprawdź szczegóły →P3000Wysoki
System baterii HV — kod nadrzędny
Układ napędowy
Sprawdź szczegóły →P0A80Krytyczny
Wymiana baterii hybrydowej — wymagana
Układ napędowy
Sprawdź szczegóły →Code P3120 appears in these brands
Go to messages and symptoms for your brand — there we analyze this code together with other typical alerts.
Suggested Hybspec services
Based on the systems affected by this code, we will most likely start with:
Sources and further reading
Does code P3120 require professional diagnostics?
The code alone is not enough. To find the cause, you need to read live data, check freeze frame conditions, and compare with vehicle behavior. Book a diagnostic session.