The oxygen sensor after the catalytic converter on bank 1 (sensor 2) is a switching sensor (about 0.1–0.9 V) used for converter monitoring and fine mixture trim. P0140 means the sensor produces no voltage of its own and the control module only sees its own reference (bias) voltage. GM's V6 sets it when the signal sits at 401–548 mV or the sensor's internal resistance exceeds 40 kΩ when it should be hot; newer GM systems apply 1900 mV and read above 1700 mV as an open circuit. Two trips. Ford reports 'no activity' under P0136 instead. A cold sensor with a failed heater can also cause it. When it fails, the control module stops the downstream trim and cannot evaluate the converter; there is no limp mode.
Medium severity. Can I keep driving?Yes, you can normally drive in moderation, but get it repaired soon: you will use more fuel and the catalytic converter can be damaged over time.
Bank 1 is the side of the engine with cylinder 1. Inline engines only have this bank. Sensor 2 is the sensor after the catalytic converter.
Symptoms
- Check engine light on (usually after two drive cycles)
- Catalyst monitor readiness not set
- Live data: sensor 2 stuck at about 450 mV (or 1.9 V)
Most likely causes
- Signal or ground wire open, connector off or corroded
- Sensor heater failed, sensor never becomes active
- Sensor worn out (no longer produces voltage)
- Control module input faulty
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- Repair difficulty: easy
- It affects emissions.
What each character of P0140 means
- P: Powertrain: engine and transmission
- 0: Generic code: same on every make
- 1: Air and fuel
- 40: Specific fault in that system
Frequently asked questions
Can I keep driving with code P0140?
Yes, you can normally drive in moderation, but get it repaired soon: you will use more fuel and the catalytic converter can be damaged over time.
What causes code P0140?
The most common causes are: signal or ground wire open, connector off or corroded; sensor heater failed, sensor never becomes active; sensor worn out (no longer produces voltage).
Related codes
- P0136O2 Sensor Circuit Bank 1 Sensor 2
- P0139O2 Sensor Circuit Slow Response Bank 1 Sensor 2
- P0141O2 Sensor Heater Circuit Bank 1 Sensor 2
- P0146O2 Sensor Circuit No Activity Detected Bank 1 Sensor 3
- P0160O2 Sensor Circuit No Activity Detected Bank 2 Sensor 2
- P0137O2 Sensor Circuit Low Voltage Bank 1 Sensor 2
Sources
- law.cornell.edu: 13 CCR 1968.2
- gsi.ext.gm.com: 18OBDG03A Engine Diagnostics
- saabwisonline.com: dtc p0137 p0138 or p0140 without lf1
- saabwisonline.com: p0136p0137 p0138 p0139p0140
Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.