P0140
O2 Sensor No Activity Detected Bank 1 Sensor 2
The engine computer is not seeing the rear oxygen sensor on Bank 1 change as expected. This usually means the sensor, wiring, or exhaust conditions are preventing a normal signal. It can also be caused by an exhaust leak or fuel mixture problem.
- SEV
- 2/5
- DRIVE
- CAUTION
- DIY
- $20–$150
- SHOP
- $150–$450
Quick answer
AI-CITATION READYWhat it means
Can you drive with it?
Most common causes
- Failed Bank 1 Sensor 2 oxygen sensor
- Damaged, corroded, or loose wiring/connectors at the sensor
- Blown fuse, open circuit, or heater circuit problem for the O2 sensor
Typical repair cost
DIY usually runs $20–$150. Typical shop repair lands around $150–$450, depending on the root cause.
01 / Definition
P0140 means the PCM detected little or no switching activity from the Bank 1 Sensor 2 oxygen sensor. This is the downstream O2 sensor, usually located after the catalytic converter on the bank that contains cylinder 1. The code points to a sensor signal problem, wiring fault, exhaust leak, or less commonly a catalytic converter or engine operating issue affecting the signal.
02 / Drive status
With caution. The vehicle is usually drivable, but the problem should be diagnosed soon. Fuel economy may drop and the emissions system may not work correctly.
03 / Symptoms
- Check Engine Light on
- Possible reduced fuel economy
- Failed emissions test
- Rough running if another engine problem is present
- No obvious drivability change in many cases
04 / Causes
| 1 | Failed Bank 1 Sensor 2 oxygen sensor | high |
|---|---|---|
| 2 | Damaged, corroded, or loose wiring/connectors at the sensor | high |
| 3 | Blown fuse, open circuit, or heater circuit problem for the O2 sensor | medium |
| 4 | Exhaust leak near the sensor or upstream of the sensor | medium |
| 5 | Catalytic converter issue affecting sensor readings | medium |
| 6 | Engine running too rich or too lean due to other faults | low |
| 7 | PCM driver or software issue | low |
05 / Diagnostic sequence
- 01Confirm the code and check for related codes such as heater circuit, fuel trim, or catalyst codes.
- 02Inspect Bank 1 Sensor 2 wiring and connector for damage, corrosion, loose pins, melted insulation, or exhaust contact.
- 03Check for exhaust leaks near the downstream sensor and around the catalytic converter.
- 04Verify the O2 sensor heater circuit has power and ground as specified by the vehicle.
- 05Use a scan tool to view Bank 1 Sensor 2 data and compare it with Bank 1 Sensor 1 and fuel trims.
- 06If the signal is flat-lined or unresponsive, test sensor resistance and wiring continuity according to factory specs.
- 07Replace the sensor if wiring and exhaust checks pass and the sensor still does not respond normally.
- 08Clear codes and road test to confirm the repair and ensure the monitor completes.
06 / Repairs
| 1 | Repair damaged wiring, terminals, or connector issues at Bank 1 Sensor 2 | $20–$150 |
|---|---|---|
| 2 | Fix exhaust leaks near the downstream O2 sensor or catalytic converter | $50–$300 |
| 3 | Replace the Bank 1 Sensor 2 oxygen sensor | $50–$250 |
| 4 | Repair heater circuit fuse, relay, or power/ground fault if present | $10–$200 |
| 5 | Diagnose and repair any engine running or catalytic converter problems causing abnormal readings | $100–$1,000+ |
07 / Related codes
08 / FAQ
What sensor is P0140 referring to?
It refers to Bank 1 Sensor 2, the downstream oxygen sensor located after the catalytic converter on the bank with cylinder 1.
Can a bad catalytic converter cause P0140?
Yes, but it is less common than a failed sensor or wiring issue. Exhaust leaks and sensor faults should be checked first.
Will P0140 cause poor fuel economy?
It can, but not always. The downstream sensor mainly monitors emissions performance, so many vehicles show little drivability change.
Should I replace the O2 sensor first?
Not always. Inspect wiring, connectors, and exhaust leaks first because those problems are common and can cause the same code.
09 / Source and method
- DATA BASIS
- OBD-II REFERENCE + OBD2.HELP
- METHOD
- STATIC VALIDATION
- SAFETY
- INFORMATIONAL
This page combines OBD-II diagnostic reference data with OBD2.help generated diagnostic guidance for code meaning, likely causes, and repair direction.
Publishing uses deterministic schema and build validation, plus manual spot checks on representative pages before release.
Safety-critical diagnosis and repairs should be confirmed with a qualified mechanic, especially when the vehicle is misfiring, overheating, or losing power.