What Does P0140 Mean?
The ECM has detected that the downstream oxygen sensor on Bank 1 (Sensor 2) is showing no activity — the signal voltage is stuck at or near a fixed value and does not change in response to variations in exhaust gas composition. This sensor should show at least minor fluctuations even when the catalytic converter is functioning properly. A flat-lined sensor cannot provide meaningful catalyst efficiency data. The driver typically will not notice any driveability symptoms.
Common Causes
40%
Failed O2 sensor (dead sensing element producing no voltage variation)
25%
O2 sensor heater failure preventing the sensor from reaching operating temperature
15%
Open circuit in the O2 sensor signal wire
10%
Severely contaminated O2 sensor element (lead, silicone, phosphorus coating)
10%
Exhaust system issue preventing exhaust gas from reaching the sensor
Diagnostic Steps
1
Monitor Bank 1 Sensor 2 live data — if the voltage is stuck at approximately 0.45V or near 0V and does not fluctuate at all during varying engine loads, the no-activity condition is confirmed.
2
Check the O2 sensor heater circuit — verify power and ground to the heater pins. If the heater is not operating, the sensor may not reach operating temperature (600°F+) and will remain inactive.
3
Backprobe the O2 sensor signal wire at the ECM connector. With the sensor disconnected, the ECM should pull the signal to a bias voltage (around 0.45V). If the bias voltage is present, the ECM input circuit is good.
4
If the heater is operational and the wiring is intact, the sensing element itself has failed. Remove and inspect the sensor — a sensor with a gray, chalky, or glazed tip is contaminated and non-functional.
5
Replace the Bank 1 Sensor 2 O2 sensor. After replacement, clear codes and perform a drive cycle to verify the new sensor produces normal oscillating or steady-state voltage patterns.
Estimated Repair Cost
$80 - $300
Parts + labor, varies by vehicle and location
The ECM has detected that the downstream oxygen sensor on Bank 1 (Sensor 2) is showing no activity — the signal voltage is stuck at or near a fixed value and does not change in response to variations in exhaust gas composition. This sensor should show at least minor fluctuations even when the cataly...
The most common cause of P0140 (02 Sensor Circuit No Activity Detected (Bank 1 Sensor 2)) is: Failed O2 sensor (dead sensing element producing no voltage variation)
Typical repair costs for P0140 range from $80 to $300, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to drive. A non-functional downstream O2 sensor does not affect engine control since this sensor is used for catalyst monitoring, not fuel trim. The vehicle will fail emissions testing.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0140 to identify the root cause.
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Quick Info
Category
Powertrain
System
Emissions / Exhaust
Difficulty
Type
Generic (SAE)
Recommended Tools
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