P0146: O2 Sensor Circuit No Activity Detected (Bank 1, Sensor 3)
Quick Answer
Safe to drive (short-term)
P0146 means the ECU cannot detect any activity from the third oxygen sensor on Bank 1, fitted after a second (usually under-floor) catalytic converter. The sensor voltage is either flatlined or out of range. Only a minority of petrol cars built to the strictest emissions standards have a Sensor 3, so this code applies to specific exhaust layouts.
- Severity
- Moderate · Emissions
- Estimated repair cost
- From €1 to €380+, varies by vehicle
€1 or €380, depending on your car.
- Replace heater fuse and diagnose underlying short€1–€90
- Replace Bank 1 Sensor 3€110–€380
A scan shows whether P0146 is really stored on your car, which codes sit next to it and how urgent each one is.
A scan needs a Bluetooth OBD2 adapter (Bluetooth LE on iPhone), about €25-60; the built-in demo runs without one. See which adapter to buy
What does P0146 mean?
P0146 is a emissions-related diagnostic trouble code classified as moderate severity.
Where it is on the car
- Engine
- Oxygen sensor before the converter (sensor 1)
- Catalytic converter
- Oxygen sensor after the converter (sensor 2, or 3 on some cars)
- Silencer and tailpipe
What are the symptoms of P0146?
- 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 Sensor 3 stuck at one value or out of range
What causes P0146?
Failed Bank 1 Sensor 3 with internal open circuit
: high
Open or broken Sensor 3 signal wire
: high
Disconnected or heavily corroded sensor connector
: medium
Failed sensor heater preventing the sensor from reaching operating temperature
: medium
Faulty ECU input circuit (rare)
: low
Is it safe to drive with P0146?
Generally yes, for short-term driving. Safe to drive short term. Sensor 3 is a monitoring sensor and does not drive fuel mixture, but the ECU loses its check on the second catalytic converter. Repair within a few weeks to maintain proper emissions diagnostics.
How do you diagnose P0146?
- Confirm the vehicle's exhaust layout. Sensor 3 is only present on cars with a third oxygen sensor after a second catalytic converter
- Inspect the Sensor 3 connector visually for disconnection, corrosion, water intrusion, or melted plastic
- Use a multimeter at the sensor connector to verify ground, heater power (battery voltage with key on), and signal continuity back to the ECU
- If wiring tests good, unplug the sensor and measure heater resistance directly. Healthy: 2-15 ohms. Open: burned-out heater. The sensor needs replacement
- If a new sensor still shows no activity, scope the signal wire for opens or shorts between the sensor and ECU
How much does P0146 cost to fix?
| Repair | Parts Cost | Labor Cost | Total Estimate | DIY Difficulty |
|---|---|---|---|---|
| Replace Bank 1 Sensor 3 | €50–€220 | €60–€160 | €110–€380 | Moderate |
| Repair sensor wiring or connector | €5–€30 | €50–€130 | €55–€160 | Moderate |
| Replace heater fuse and diagnose underlying short | €1–€10 | €0–€80 | €1–€90 | Easy |
Prices estimated as of October 2026. Costs vary by region, vehicle, and shop.
Related diagnostic codes
Common questions about P0146
- What does no activity detected mean?
- The ECU expects the Sensor 3 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. Most often the sensor has failed internally or a wire has broken.
- Can I drive with P0146?
- Yes, short term. Sensor 3 does not drive fuel mixture, so the car runs normally. Long term you lose the ECU's check on the second catalytic converter, which may mask a developing converter problem.
- Why does my car have three O2 sensors per bank?
- Most cars do not. Some petrol cars built to the strictest emissions standards have a second catalytic converter further down the exhaust, with a third oxygen sensor after it to monitor it. On diesel vans such as the Sprinter, Transit and Crafter, the sensors after the SCR catalyst are NOx sensors, which report their own fault codes rather than P0146.
- Can a blown fuse cause P0146?
- Indirectly yes. If the heater fuse is blown, the sensor never reaches operating temperature and stays inactive, triggering P0146 alongside heater codes like P0147. Check the heater fuse first if you see both code types.