P0140: O2 Sensor Circuit No Activity Detected Bank 1 Sensor 2
A generic powertrain (engine and transmission) trouble code, same meaning on every brand.
Yes - fuelling is unaffected, but the catalytic converter is no longer being monitored.
Symptoms
- Check engine light only
- Emissions test failure
- No driveability change
Likely causes, most common first
- Open circuit in the downstream sensor wiring
- Failed sensor heater
- Blown fuse feeding the heater circuit
- Connector unplugged after exhaust work
Read P0140 yourself before paying for diagnosis
A basic Bluetooth OBD-II scanner ($20-40) plugs into the port under the dashboard and shows this code with live sensor data on your phone - useful both for confirming the fix and for talking to a shop from an informed position.
What is going on and how it gets diagnosed
P0140 reports no activity from the bank 1 downstream sensor. Because this sensor sits far from the engine, its exhaust gas is cooler and its internal heater matters even more than on the upstream sensor - a dead heater alone is enough to set this code.
If the code appeared shortly after exhaust or suspension work, check the connector first. These are among the easiest connectors to leave unplugged or to snag during a repair, and an unplugged sensor costs nothing to fix.
Repair options and cost
Typical US independent-shop ranges, parts and labor. Dealers run higher; regional labor rates vary.
Cars that report P0140 most often
Based on mentions of this code in NHTSA owner complaints.
Frequently asked questions
Can I drive with P0140?
Yes - fuelling is unaffected, but the catalytic converter is no longer being monitored.
How much does it cost to fix P0140?
Typical US repair costs range from $20 for the simplest fix (downstream oxygen sensor) to $400 in the worst case. The right number depends on which cause your car has - see the causes list.
Related codes
The codes closest to P0140. They often appear together, and telling them apart is usually what narrows the diagnosis.
Definition per SAE J2012 standard nomenclature. Symptoms, causes and costs are editorial guidance - always confirm with a diagnosis of your specific vehicle.