What it means
The module detects no activity from the downstream oxygen sensor on bank 1 under the monitored conditions.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Bank 1 Sensor 2 is the oxygen sensor after the catalytic converter on bank 1; the module uses its signal to assess exhaust oxygen and catalyst performance. P0140 sets when the downstream signal shows too little activity under the conditions in which the module expects it to change.
Common causes
Most likely first.
- Sensor aged or poisoned
- Sensor heater circuit weak
- Catalytic converter so degraded that downstream signal mirrors upstream
Symptoms
- Check engine light on
- Failed emissions test
How to diagnose it
- Use a scan tool to review freeze-frame data and compare live Bank 1 Sensor 2 activity with the upstream sensor once the exhaust is warm.
- Inspect the downstream sensor connector and harness for corrosion, loose pins, heat damage, or contact with the exhaust.
- Check the sensor heater fuse, wiring, and operation because a weak heater can keep Sensor 2 from reaching its working temperature.
- Check for exhaust leaks near the sensor that could distort its reading, and look for related fuel-trim or oxygen-sensor codes.
- If wiring, heater operation, and exhaust integrity are sound, assess the sensor response and catalyst condition using the manufacturer's diagnostic procedure.
Common fixes
- Repair damaged or loose Bank 1 Sensor 2 wiring or connector pins.
- Replace a failed heater fuse or repair its circuit fault.
- Repair an exhaust leak near the downstream sensor.
- Replace a slow or contaminated Bank 1 Sensor 2.
- Repair or replace a catalyst confirmed to be degraded.
Can I keep driving?
With only the warning light and no change in how the engine runs, short trips are generally reasonable, but arrange diagnosis because emissions monitoring may be unreliable. Avoid delaying an emissions test; a degraded catalyst or developing engine fault can cause further damage.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.