P241B

Code

Generic P — Powertrain

O2 Sensor Signals Swapped Bank 2 Sensor 1/Bank 2 Sensor 2

Brand: Generic

Type: P — Powertrain

Views: UK: 24 EN: 30 RU: 29

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Bank 2 sensor connectors or wiring are swapped at a harness repair or connector
Upstream (Sensor 1) and downstream (Sensor 2) sensors installed in the wrong ports
Aftermarket extension harness or repair harness with pins incorrectly pinned
ECM connector pins incorrectly seated or swapped
Previous service technician swapped sensors or connectors during repair
Corroded or damaged harness causing cross signals

Symptoms

Check Engine Light (MIL) illuminated
Stored P241B along with possible other O2-related codes
Failed emissions/SMOG test or incorrect readiness
Possible poor fuel economy
Possible rough idle or hesitation if ECU fueling is affected
O2 sensor PID values show upstream/downstream behavior inconsistent with location

What to check

Read freeze frame and related O2 sensor codes with a scan tool
Visually inspect B2S1 and B2S2 connectors, wiring and sensor locations for obvious swaps or damage
Verify sensor part numbers and that sensors are installed in correct ports (upstream vs downstream)
Backprobe sensor signal and heater circuits and compare to expected voltages/behavior
Compare live O2 sensor data for switching rate and amplitude between B2S1 and B2S2
Check continuity and pinout between each sensor connector and ECM pins

Signal parameters

Bank 2 Sensor 1 (upstream) expected (narrowband): rapid switching ~0.1–0.9 V when warmed, frequency several cycles/sec during closed-loop
Bank 2 Sensor 2 (downstream, post-cat) expected: much steadier voltage near ~0.4–0.6 V or less switching; should track but not mimic upstream switching
Heater circuit resistance typically ~2–20 ohms (varies by sensor); heater voltage present during key-on/on
Continuity: each sensor signal pin should show low resistance to its corresponding ECM pin and high resistance to other sensor signal pins

Diagnostic algorithm

Verify code and related O2/catalyst codes with a scan tool; note freeze frame values.
Monitor live data for B2S1 and B2S2: confirm which sensor is exhibiting upstream rapid switching vs downstream steady behavior.
Visually inspect both sensors and harness: confirm sensors are mounted in correct upstream/downstream locations and connectors are not swapped.
With ignition on (engine off), backprobe sensor connectors: verify heater supply and ground, and measure signal voltage at key-on and while running to see which circuit shows upstream characteristics.
If suspicion of swapped connectors: disconnect at harness splice/ECM and verify pin-to-pin continuity from each sensor to the ECM to confirm correct pinout; repair incorrect pinning.
If harness repair or extension present, inspect and correct pin order or replace faulty harness. Repair damaged wires or insulation and protect against shorting.
If necessary, temporarily swap connector leads at the harness (or swap sensors at the harness end) to see if the code follows the physical sensor or the harness position—only do this safely with ignition off and when engine is cool.
After repairs, clear codes and perform a road test and smoke/check readiness: confirm B2S1 shows upstream switching and B2S2 shows downstream behavior and that code does not return.
If wiring and connectors check good and behavior still incorrect, inspect ECM connector for damaged pins or consider ECM-related diagnosis per manufacturer procedures.

Likely causes

Physical swap of B2S1 and B2S2 connectors or sensors
Replacement sensor installed in wrong position
Harness repair with pins installed in incorrect order
Connector mates reversed on a multi-sensor connector
Failure of insulation causing signals to be cross-coupled

Fault status

⚠️ Status

O2 sensor signal circuits for Bank 2 Sensor 1 and Bank 2 Sensor 2 are detected in swapped or unexpected configuration; verify sensor installation and wiring/pinout.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-2.5 hours