P1131 — HO2S Circuit Low Variance Bank 1 Sensor 2

Diagnostic algorithm

1. Verify the code and related codes. Record freeze frame and live data for Bank 1 Sensor 1 and Sensor 2.
2. Compare live voltages: Sensor 1 should switch rich/lean rapidly; Sensor 2 should show damped but measurable variation. If both are flat, suspect upstream problem or fuel/engine issue.
3. Inspect the Bank1 Sensor2 connector and wiring for corrosion, breaks, or pin damage. Repair any physical damage.
4. Test sensor heater: with connector disconnected, measure heater resistance and compare to OEM spec. With ignition on, verify heater supply voltage and ground switching per service manual.
5. Backprobe signal wire and observe voltage with a scan tool or meter while varying engine load (idle, rev, introduce slight enrichment safely). Note any change. Do not perform unsafe enrichment procedures.
6. Wiggle harness from sensor to ECM while monitoring signal to find intermittent wiring issues.
7. Check for exhaust leaks upstream of the downstream sensor — repair any leaks and re-test.
8. Evaluate catalytic converter efficiency (compare front vs rear sensor behavior). If front sensor switches normally and rear is flat, cat may be degraded.
9. If wiring and vehicle systems check good, replace the Bank1 Sensor2 with OEM or equivalent sensor and recheck. Clear codes and road test to verify code does not return.
10. If problem persists after sensor replacement, perform PCM/harness continuity checks to PCM and consider PCM diagnosis per factory procedures.