P0140 code meaning
O2 Sensor Circuit No Activity Detected Bank 1 Sensor 2
Powertrain system Generic code P01xx codes Check engine light
What P0140 means
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.
P0140 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyEasy, DIY possible
- Typical labor0.3 to 1.5 hours
- Clears after repairAfter a drive cycle
Symptoms of P0140
- 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)
Common causes of P0140
- Most likelySignal or ground wire open, connector off or corroded
- PossibleSensor heater failed, sensor never becomes active
- PossibleSensor worn out (no longer produces voltage)
- Less likelyControl module input faulty
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Oxygen sensor bank1 sensor2Oxygen sensor wiringCatalytic converter
What each part of P0140 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 1 | Area: fuel and air metering. |
| 40 | The exact fault in that area. |
What to do next
- Note P0140 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0140
What does P0140 mean?
P0140 means "O2 Sensor Circuit No Activity Detected Bank 1 Sensor 2". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with P0140?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will P0140 fail an emissions test?
Yes, it can. P0140 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P0140 to fix?
Difficulty: easy. A typical repair takes 0.3 to 1.5 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P0140 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.