P2272: O2 Sensor Signal Biased/Stuck Lean (Bank 2, Sensor 2)
P2272 means the oxygen sensor behind the catalytic converter on bank 2 stayed at a lean (low fuel) reading when the engine computer tried to make the mixture rich. The check engine light comes on, but the code does not cause limp mode, and it most often points to a worn or contaminated rear sensor.
You can drive, but get it checked soon
The data lists no limp mode for this code, so the car usually drives normally. The fault affects emissions monitoring, so have it checked soon rather than ignoring the light, since a second problem could be hidden behind it.
What it means
Bank 2 is the side of a V or flat engine that does not contain cylinder 1. Sensor 2 is the oxygen sensor after the catalytic converter (the part that cleans exhaust). To test this sensor, the engine computer (ECM) briefly adds extra fuel on bank 2 and expects the rear sensor voltage to rise to a rich reading. If the sensor stays low, the ECM sets P2272. One GM table, for example, sets the code if the voltage is still under 800 mV after 68 g of air during this forced enrichment. Ford uses a 0.42 V limit, the same as on bank 1. If only bank 2 reports a fault, comparing its live data with bank 1 helps narrow down the cause.
Likely causes
- Bank 2 rear oxygen sensor aged or contaminatedVery likely
A worn or fouled sensor responds slowly or not at all, so it stays low when the ECM enriches the mixture.
- Engine oil in the sensor connector, for example from a leaking oil pressure switchPossible
Oil that gets into the connector can disturb the sensor signal; Mazda found this on the 2007 to 2015 CX-9, where a leaking oil pressure switch was the source, and fixed it with a new switch and a cleaned connector.
- Exhaust leak on bank 2 ahead of the rear sensorPossible
A leak can let outside air into the exhaust, which makes the sensor read lean.
What you may notice
- Check engine light (malfunction indicator lamp) on
- Catalyst monitor for bank 2 not completing
What to check, cheapest first
- 1Read the stored codes and freeze frame data, and note whether related codes such as P2273, P2A04 or P0157 are also present. · you can do it
- 2Look at the bank 2 rear sensor wiring and connector for damage, and check the connector for oil or moisture. · you can do it
- 3Listen and look for an exhaust leak on bank 2 between the engine and the rear sensor, such as a hissing or soot marks at joints. · you can do it
- 4Compare live data from the bank 2 rear sensor with bank 1 while the engine is warm, to see whether only bank 2 stays low. · mechanic
- 5If oil is in the connector, find the source (for example a leaking oil pressure switch), repair it and clean the connector. · mechanic
- 6Replace the bank 2 rear sensor if wiring and exhaust are fine, then clear the code and complete a drive cycle to confirm the repair. · mechanic
Related codes
Frequently asked questions
Can I keep driving with P2272?+
Usually yes for a short time, since limp mode is not listed for this code. Get it diagnosed soon so the cause does not get worse or hide other faults.
Can a loose gas cap cause P2272?+
The data does not list the gas cap as a cause. This code points to the bank 2 rear oxygen sensor, its connector or an exhaust leak.
Will P2272 pass an emissions test?+
Unlikely. The code is emissions related and turns the check engine light on. The catalyst monitor for bank 2 may also not complete, which can cause a test failure.
Can I fix it myself?+
Possibly. The repair is rated medium difficulty and DIY is possible, with an estimated 0.3 to 2 hours. A drive cycle is needed afterward to confirm the fix.
Written with the help of AI from the public OBDex definition (CC0). Each make may use the code differently. Updated: 2026-11-10