Emissions

P0140 — O2 Sensor No Activity Detected (Bank 1 Sensor 2)

Severity: low Safe to drive

What P0140 means

The downstream oxygen sensor sits after the catalytic converter and helps the PCM judge how well the converter works. P0140 sets when the Bank 1 Sensor 2 signal stays flat or out of range and does not respond to changes in exhaust content. The usual culprits are the sensor itself, its heater circuit or its wiring.

Symptoms

  • Check engine light on
  • Failed emissions test
  • Slightly worse fuel economy
  • Occasional rough idle
  • P0420 or P0430 may appear alongside

Possible causes

  1. Failed Bank 1 Sensor 2 oxygen sensor
  2. Damaged wiring or a corroded or loose connector
  3. Open sensor heater circuit or blown fuse
  4. Exhaust leak ahead of the sensor
  5. Failed or contaminated catalytic converter skewing the signal
  6. Rarely, a PCM fault

How to diagnose

  1. Scan for codes and freeze frame data, and note any others (P0420, P0141)
  2. Inspect the sensor wiring and connector for chafing, melting and corrosion
  3. Check the heater fuse and power supply to the sensor
  4. Measure heater resistance with a multimeter
  5. Watch live data: sensor voltage should respond to changes in engine load
  6. Look for exhaust leaks upstream of the sensor
  7. Review fuel trims and catalytic converter condition
  8. Check the ground and signal wires back to the PCM

Common fixes

  • Replace the Bank 1 Sensor 2 oxygen sensor
  • Repair the wiring or connector
  • Replace the heater fuse after finding why it blew
  • Fix the exhaust leak
  • Replace the catalytic converter if it is confirmed bad
  • Diagnose or replace the PCM only after ruling out everything else

Questions and answers

Can I drive with a P0140 code?

Usually yes, since handling isn't affected. Still, fix it soon so you can pass an emissions test and avoid missing a catalytic converter problem.

What should I check first for P0140?

Inspect the downstream sensor's wiring and connector and look for exhaust leaks nearby. Then check live data and the sensor's heater circuit.

Does P0140 mean I need a new catalytic converter?

Normally no, the sensor or wiring is the more likely cause. Check the converter if P0420 or P0430 shows up after the sensor is replaced.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.