P241A
O2 Sensor Signals Swapped Bank 1 Sensor 1 and Sensor 2
The pre- and post-catalyst lambda signals on bank 1 are swapped - the upstream sensor responds like a downstream sensor and vice versa. Typically the harness was reversed during a sensor change.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: easy
Symptoms
- Check engine light on
- Increased fuel consumption
- Possible rough idle or hesitation
- Failed emissions test
Common causes
Ordered by how often each turns out to be the cause.
- Harness swapped during repairCommon
Parts involved
- Oxygen Sensor B1s1
- Oxygen Sensor B1s2
P241A is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.