P0138: O2 Sensor Circuit High Voltage (Bank 1, Sensor 2)

P0138 means the downstream oxygen sensor on Bank 1 (post-catalyst, Sensor 2) is reporting a voltage that is too high for too long, above roughly 1.0V. A healthy downstream sensor reads around 0.6–0.8V steady. Persistent high voltage typically indicates a rich exhaust condition, a short to voltage in the wiring, or a contaminated sensor.

P0138 è un codice diagnostico di guasto relativo a emissioni, classificato con gravità moderate. Quando la centralina (ECU) del tuo veicolo rileva questa condizione, memorizza P0138 e accende la spia motore.

Se il tuo veicolo ha attivato P0138, potresti notare uno o più di questi sintomi:

• Check engine light illuminated
• Increased fuel consumption
• Black smoke or strong fuel smell from exhaust in severe cases
• Possible failed emissions test
• May appear with P0172 or P0175 if the engine is genuinely running rich

Ecco le cause più comuni di P0138, ordinate in base alla probabilità che siano la causa del problema:

In genere sì, per brevi tragitti. Safe to drive short term. A high downstream signal usually points to a rich condition reaching the sensor, a shorted sensor, or a failing catalytic converter. Long-term rich running can clog the converter, so do not ignore this for more than a few weeks.

Segui questi passaggi per individuare la causa principale di P0138:

1. Read freeze frame data and check for companion codes (P0172, P0175, P0420) that point to a real rich condition or converter problem
2. Use a scan tool to view downstream sensor voltage. A reading stuck above 0.9V at idle indicates a rich condition or a faulty sensor
3. Check long-term fuel trims. If LTFT is significantly negative (under -10%), the engine is genuinely running rich
4. Inspect the Bank 1 Sensor 2 signal wire for shorts to voltage, especially near heat shields and the battery positive cable
5. Substitute a known-good sensor. If high voltage persists, the issue is fuel mixture or wiring, not the sensor

I costi di riparazione di P0138 variano a seconda della causa principale e del tuo veicolo. Ecco le stime tipiche:

P0138 si comporta in modo diverso a seconda del tuo veicolo. Seleziona la tua auto qui sotto per cause specifiche del modello, problemi noti e stime dei costi adeguate:

Questi codici compaiono spesso insieme a P0138 o indicano problemi correlati: