P0140 — O2 Sensor Circuit No Activity Detected (Bank 1 Sensor 2)
Can drive — fix at your convenience.
What P0140 means
This code means the engine computer sees no signal activity from the downstream oxygen sensor on Bank 1 (Sensor 2), as if the sensor isn't responding at all. The usual causes are a dead or unheated sensor, an open or broken wire, or a bad connector, and sometimes a blown fuse on the sensor's heater circuit. The fix most often involves replacing the oxygen sensor or repairing the wiring that feeds it.
Common symptoms
- Check engine light is on
- Slightly reduced fuel economy
- Failed emissions or smog test
- No obvious change in how the car drives
- Catalytic converter monitoring shows as incomplete
Common causes
- Dead or failed downstream oxygen sensor
- Open or broken wire in the sensor circuit
- Faulty or corroded connector
- Blown fuse on the sensor heater circuit
- Less often, an engine computer fault
Typical repair cost
$150 – $400
Varies by vehicle and root cause.
Frequently asked questions
Can I keep driving with a P0140 code?
Generally yes, for the short term. The sensor that triggered it monitors emissions instead of running the engine, so the car should drive fine. Have it checked within a week or two, and know that an emissions test will almost certainly fail until it's resolved.
How much does it cost to fix a P0140 code?
Most fixes run between $150 and $400. Replacing the oxygen sensor is the common repair and makes up most of the cost. If it turns out to be a fuse, wire, or connector, the bill can be noticeably lower.
Is a P0140 code serious?
It's a low-severity code. The engine isn't at risk and you can keep driving short term, but it does disable proper emissions monitoring and can slightly lower fuel economy. It's best to fix it promptly so it doesn't mask a converter or exhaust issue.
Why does P0140 mean no activity from the sensor?
The computer expects the downstream sensor's voltage to fluctuate as exhaust conditions change. When that signal stays flat or absent, it sets P0140, often because the sensor is dead, unheated, or disconnected by a broken wire. A scan tool reading the sensor's live data quickly confirms whether it's responding.