1. What’s P0140?

Code P0140 signifies “No Activity Detected” in the downstream oxygen sensor (Bank 1, Sensor 2) circuit. This sensor, located after the catalytic converter, monitors its efficiency. If it gives a flatline—or no voltage change—the ECM assumes the circuit is faulty.

2. Causes & Real-World Examples

• Expired or dead Bank 1 Sensor 2 oxygen sensor.
• Wiring corrosion or connector issue—often from road salt or exposure.
• Exhaust leak between the sensor and catalytic converter interfering with readings.
• Faulty ECM or grounding point not recognizing the sensor output.

In one case, a VW Golf owner noticed a failed emissions test but no drivability issues. Diagnosis revealed the wire insulation had worn away—replacing the harness restored sensor activity.

3. Symptoms

• Check Engine Light illuminated
• Emissions test failure
• Possible slight increase in fuel consumption
• No apparent loss in power or drivability

4. Diagnostic Steps

1. Use iCarzone UR1000 to confirm P0140 and capture live voltage from the downstream O₂ sensor.
2. Check for voltage swings—should move between 0.1–0.9V under rich/lean conditions.
3. Evaluate wiring continuity and connector corrosion.
4. Look for exhaust leaks that could skew readings.
5. Test the sensor heater circuit for proper power and resistance.

5. Fixes

• Replace failing downstream O₂ sensor with OEM-spec part.
• Repair or replace damaged harness or corroded connectors.
• Fix exhaust leaks affecting sensor accuracy.
• Use UR1000 to clear code and verify the circuit is active post-repair.

6. Pro Tips

Always wear gloves and disconnect the battery before handling O₂ sensors. Use UV dye spray on connectors to spot hairline cracks. Re-test with UR1000 afterward to confirm successful job.