What it means
The control module detects that the signals for oxygen sensors 1 and 2 on bank 1 appear to be reversed. This can occur if their connections are crossed; the code does not identify the repair history.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Bank 1 Sensor 1 is the upstream oxygen sensor before the catalytic converter, while Bank 1 Sensor 2 is downstream of it. The control module compares their signals and sets P241A when the two appear reversed, which can result from crossed connectors, incorrect wiring, or sensors installed in the wrong positions.
Common causes
Most likely first.
- Sensor 1 and 2 connectors crossed
- Wiring connected incorrectly
- Incorrect sensor installation
Symptoms
- Check engine light on
- Increased fuel consumption
- Possible rough idle or hesitation
- Failed emissions test
How to diagnose it
- Record freeze-frame data and check related oxygen-sensor, fuel-trim, and catalyst codes before clearing the fault.
- Locate Bank 1 Sensors 1 and 2 using vehicle information, then inspect their connectors and harness routing along the exhaust.
- Check whether the upstream Sensor 1 and downstream Sensor 2 connectors have been crossed or the sensors installed in the wrong positions.
- Compare live data from both bank 1 sensors during warm operation to confirm whether the upstream and downstream responses appear reversed.
- Trace the wiring and test signal continuity and pin assignment against the wiring diagram, then check sensor operation if routing is correct.
Common fixes
- Reconnect Bank 1 Sensor 1 and Sensor 2 to their correct connectors.
- Correct crossed or misrouted wiring between the two bank 1 sensor circuits.
- Reinstall a sensor in its intended upstream or downstream position.
- Replace a failed sensor only after confirming correct wiring and connector assignment.
Can I keep driving?
The vehicle may be driveable, but reversed bank 1 sensor signals can disrupt mixture control and emissions monitoring, potentially worsening fuel economy or running quality. Avoid extended driving if it misfires or runs very roughly because unburned fuel can damage the catalytic converter.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.