Emission controls · Powertrain · generic (SAE-defined)
P0140: O2 Sensor Circuit No Activity Detected (Bank 1 Sensor 2)
P0140 means the engine computer sees no meaningful signal from the downstream oxygen sensor after the bank 1 catalytic converter, often because of an open circuit or failed sensor.
Standard title per SAE J2012 / ISO 15031-6 · Updated 2026-11-07 · By CarWhere Research
How P0140 sets
The powertrain control module (PCM) applies a small reference or bias voltage to the bank 1 sensor 2 oxygen (O2) sensor circuit. When the sensor is working, its output moves away from that bias as the exhaust changes. If the signal sits at the bias value for too long once the engine is warm, the PCM assumes the sensor or circuit is inactive and sets P0140. Specific values are manufacturer-specific.
Common causes of P0140
Roughly most likely first; the actual cause depends on the vehicle and needs testing to confirm.
- Open signal or ground circuit, often a broken wire under the vehicle
- Failed bank 1 sensor 2 oxygen sensor
- Heater not working, so the sensor never warms up
- Disconnected or corroded connector
- Blown heater fuse
P0140 symptoms
- Check engine light on
- Usually no drivability symptoms
- Possible heater circuit code stored at the same time
How P0140 is diagnosed
- Scan for codes; a heater code alongside P0140 suggests the sensor is not reaching operating temperature.
- Inspect wiring routed along the floor and exhaust for breaks, snags or melted sections.
- Check that the connector is plugged in and free of corrosion.
- Watch the sensor on live data during a warm drive; a flat line confirms inactivity.
- Test continuity of the signal and ground circuits and measure heater resistance.
Typical fixes for P0140
- Repair open wiring or a damaged connector
- Replace the bank 1 sensor 2 oxygen sensor
- Replace a blown fuse and repair the cause of the short
Replace parts only after testing confirms the cause — a code names the circuit or condition that failed a check, not necessarily the faulty part. We don’t publish per-repair prices; for what households actually spend on upkeep, see car repair costs.
Related codes & warning lights
P0140 FAQ
What does code P0140 mean?
P0140 means the engine computer sees no meaningful signal from the downstream oxygen sensor after the bank 1 catalytic converter, often because of an open circuit or failed sensor. The standard definition is "O2 Sensor Circuit No Activity Detected (Bank 1 Sensor 2)."
Can I drive with a P0140 code?
Yes, generally. Drivability is rarely affected, but the catalyst monitor cannot run, so expect an emissions test failure until it is fixed.
Is P0140 usually the sensor or the wiring?
Both are common. Downstream sensor wiring is exposed to road debris and heat, so inspect it carefully before replacing the sensor.
Does P0140 affect my catalytic converter?
It does not harm the converter, but it prevents the engine computer from checking the converter, which keeps the catalyst readiness monitor from completing.
Keep researching
More emission controls codes
Sources
- SAE J2012 — Diagnostic Trouble Code Definitions (standard code titles)
- ISO 15031-6 — Road vehicles: communication between vehicle and external equipment for emissions-related diagnostics, Part 6: Diagnostic trouble code definitions
- U.S. EPA — Vehicle Emissions Inspection and Maintenance (I/M) programs
- U.S. EPA, 40 CFR 86.1806-17 — Federal onboard diagnostics requirements for light-duty vehicles
- California Air Resources Board — On-Board Diagnostic (OBD) Program
General information written by CarWhere Research, not a diagnosis of your vehicle. Manufacturers can add their own sub-definitions and test conditions; confirm with the factory service information for your year, make and model. Before paying for a repair, check NHTSA for open recalls and your warranty booklet: federal law requires an emissions warranty on major emission-control parts such as the catalytic converter and engine computer.