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DTC/P0140

P0140: O2 Sensor Circuit No Activity Detected (Bank 1, Sensor 2)

Quick Answer
Moderata GravitàSicuro da guidare (a breve termine)Emissioni

P0140 means the ECU cannot detect any activity from the downstream oxygen sensor on Bank 1 (post-catalyst, Sensor 2). The sensor voltage is either flatlined or out of range. This usually points to a failed sensor, an open circuit in the wiring, or a connector that has come loose or corroded.

Costo di riparazione stimatoDa €1 a €310+, varia in base al veicolo

Cosa significa P0140?

P0140 means the ECU cannot detect any activity from the downstream oxygen sensor on Bank 1 (post-catalyst, Sensor 2). The sensor voltage is either flatlined or out of range. This usually points to a failed sensor, an open circuit in the wiring, or a connector that has come loose or corroded.

P0140 è un codice diagnostico di guasto relativo a emissioni, classificato con gravità moderate. Quando la centralina (ECU) del tuo veicolo rileva questa condizione, memorizza P0140 e accende la spia motore.

Quali sono i sintomi di P0140?

Se il tuo veicolo ha attivato P0140, potresti notare uno o più di questi sintomi:

  • Check engine light illuminated
  • Slight reduction in fuel economy in some cases
  • Possible failed emissions test
  • Usually no noticeable change in how the car drives
  • Live data shows downstream sensor stuck at one value or out of range

Cosa causa P0140?

Ecco le cause più comuni di P0140, ordinate in base alla probabilità che siano la causa del problema:

altaFailed downstream O2 sensor (Bank 1, Sensor 2) with internal open circuit
altaOpen or broken O2 sensor signal wire
mediaDisconnected or heavily corroded sensor connector
mediaFailed sensor heater preventing sensor from reaching operating temperature
bassaFaulty ECU input circuit (rare)

È sicuro guidare con P0140?

In genere sì, per brevi tragitti. Safe to drive short term. The downstream sensor reporting no activity does not affect fuel mixture, but the ECU loses its catalyst monitoring capability. Repair within a few weeks to maintain proper emissions diagnostics.

Come si diagnostica P0140?

Segui questi passaggi per individuare la causa principale di P0140:

  1. Read freeze frame data and check for companion heater codes (P0141, P0155) that would point to a power issue at the sensor
  2. Inspect the Bank 1 Sensor 2 connector visually for disconnection, corrosion, water intrusion, or melted plastic
  3. Use a multimeter at the sensor connector to verify ground, heater power (battery voltage with key on), and signal continuity back to the ECU
  4. If wiring tests good, unplug the sensor and measure heater resistance directly. Healthy: 2–15 ohms. Open: burned-out heater. The sensor needs replacement
  5. If a new sensor still shows no activity, scope the signal wire for opens or shorts between the sensor and ECU

Quanto costa riparare P0140?

I costi di riparazione di P0140 variano a seconda della causa principale e del tuo veicolo. Ecco le stime tipiche:

Riparazione Costo dei ricambi Costo della manodopera Stima totale Difficoltà fai-da-te
Replace downstream O2 sensor (Bank 1, Sensor 2) €40–€180 €50–€130 €90–€310 Moderata
Repair O2 sensor wiring or connector €5–€25 €40–€120 €45–€145 Moderata
Replace heater fuse and diagnose underlying short €1–€10 €0–€80 €1–€90 Facile

Prezzi stimati al March 2026. I costi variano in base alla regione, al veicolo e all'officina.

P0140 su veicoli specifici

P0140 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:

BMW

P0140 su BMW 3 Series

2006–2024

On N52 and N55, the downstream sensor connector clip is fragile and frequently breaks on older cars. A broken clip lets the connector vibrate loose, which presents as P0140 (no activity) even though the sensor itself is fine. Inspect and re-secure the connector before condemning the sensor. BMW OEM Bosch sensors 110–200 euros, aftermarket Bosch around 60–110 euros.

Cosa causa P0140 su una BMW 3 Series?

BMW 3 SeriesBroken connector clip on N52/N55 causing intermittent disconnection
BMW 3 SeriesHeater element burnout at 150,000+ km producing flat signal

Costo di riparazione di P0140 per BMW 3 Series

Costi stimati per i proprietari di BMW 3 Seriesadeguato al rialzo rispetto alla media a causa dei prezzi dei ricambi specifici BMW

Riparazione Costo dei ricambi Costo della manodopera Stima totale Difficoltà fai-da-te
Replace downstream O2 sensor (Bank 1, Sensor 2) €56–€252 €70–€182 €126–€434 Moderata
Repair O2 sensor wiring or connector €7–€35 €56–€168 €63–€203 Moderata
Replace heater fuse and diagnose underlying short €1–€14 €0–€112 €1–€126 Facile

Prezzi stimati al March 2026. I costi variano in base alla regione, al veicolo e all'officina.

Volkswagen

P0140 su Volkswagen Golf

2005–2024

EA888 TSI engines see P0140 most often from heater element burnout combined with oil-contaminated sensor element. Check the heater fuse first, then heater resistance at the sensor before buying parts. On older MK5/MK6 cars, the sensor harness can chafe against the heat shield, breaking the signal wire and producing P0140.

Cosa causa P0140 su una Volkswagen Golf?

Volkswagen GolfHeater element burnout accelerated by EA888 oil consumption
Volkswagen GolfWire chafing against heat shield on MK5/MK6 chassis

Costo di riparazione di P0140 per Volkswagen Golf

Costi stimati per i proprietari di Volkswagen Golfadeguato al rialzo rispetto alla media a causa dei prezzi dei ricambi specifici Volkswagen

Riparazione Costo dei ricambi Costo della manodopera Stima totale Difficoltà fai-da-te
Replace downstream O2 sensor (Bank 1, Sensor 2) €46–€207 €57–€150 €103–€357 Moderata
Repair O2 sensor wiring or connector €6–€29 €46–€138 €52–€167 Moderata
Replace heater fuse and diagnose underlying short €1–€12 €0–€92 €1–€103 Facile

Prezzi stimati al March 2026. I costi variano in base alla regione, al veicolo e all'officina.

Audi

P0140 su Audi A4

2006–2024

On the B7 and B8 A4 with 2.0 TFSI, the downstream sensor connector lives in a tight spot near the gearbox bellhousing and is prone to being knocked loose during clutch or gearbox work. Check for incomplete seating before replacing the sensor if P0140 appeared after recent work. Audi-OEM sensors 130–220 euros, aftermarket Bosch around 70–120 euros.

Cosa causa P0140 su una Audi A4?

Audi A4Connector knocked loose during gearbox or clutch work
Audi A4Heater burnout on EA888 at 150,000+ km

Costo di riparazione di P0140 per Audi A4

Costi stimati per i proprietari di Audi A4adeguato al rialzo rispetto alla media a causa dei prezzi dei ricambi specifici Audi

Riparazione Costo dei ricambi Costo della manodopera Stima totale Difficoltà fai-da-te
Replace downstream O2 sensor (Bank 1, Sensor 2) €50–€225 €63–€163 €113–€388 Moderata
Repair O2 sensor wiring or connector €6–€31 €50–€150 €56–€181 Moderata
Replace heater fuse and diagnose underlying short €1–€13 €0–€100 €1–€113 Facile

Prezzi stimati al March 2026. I costi variano in base alla regione, al veicolo e all'officina.

Mercedes-Benz

P0140 su Mercedes C-Class

2007–2024

The W204 M271 1.8L Kompressor commonly triggers P0140 from heater element burnout around 130,000–150,000 km. The W205 OM651 diesel has the documented harness chafing point near the gearbox mount that can sever the signal wire, producing P0140. Mercedes-OEM Bosch sensors 130–220 euros, aftermarket Bosch around 70–120 euros.

Cosa causa P0140 su una Mercedes C-Class?

Mercedes C-ClassHeater burnout on W204 M271 at 130,000+ km
Mercedes C-ClassHarness chafing on W205 OM651 severing signal wire

Costo di riparazione di P0140 per Mercedes C-Class

Costi stimati per i proprietari di Mercedes C-Classadeguato al rialzo rispetto alla media a causa dei prezzi dei ricambi specifici Mercedes-Benz

Riparazione Costo dei ricambi Costo della manodopera Stima totale Difficoltà fai-da-te
Replace downstream O2 sensor (Bank 1, Sensor 2) €54–€243 €68–€176 €122–€419 Moderata
Repair O2 sensor wiring or connector €7–€34 €54–€162 €61–€196 Moderata
Replace heater fuse and diagnose underlying short €1–€14 €0–€108 €1–€122 Facile

Prezzi stimati al March 2026. I costi variano in base alla regione, al veicolo e all'officina.

Questi codici compaiono spesso insieme a P0140 o indicano problemi correlati:

P0136P0137P0138P0139P0141P0420

Domande frequenti su P0140

What does no activity detected mean?

The ECU expects the downstream O2 sensor signal to move within a defined range over time. If the voltage stays flat or out of range for the full monitor window, the ECU concludes the sensor has no activity and sets P0140. Most often the sensor itself has failed internally, or a wire has broken.

Can I drive with P0140?

Yes, short term. The downstream sensor does not drive fuel mixture, so the car runs normally. Long term you lose catalytic converter monitoring, which means you may miss a developing converter problem until it is severe.

How do I test an O2 sensor with a multimeter?

Unplug the sensor and measure heater resistance (typically 2–15 ohms). Plug it back in and back-probe the signal wire. With the engine warm and idling, a healthy downstream sensor reads around 0.6–0.8V steady. A flat reading at 0V or 5V with engine running points to an internal sensor failure.

Can a blown fuse cause P0140?

Indirectly yes. If the heater fuse is blown, the sensor never reaches operating temperature and stays inactive, triggering P0140 alongside heater codes like P0141. Check the heater fuse first if you see both code types.

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