P0130O2 sensor circuit fault (Bank 1, Sensor 1)

Means the ECM sees a problem in the Bank 1 Sensor 1 oxygen sensor circuit—the upstream probe that switches rich/lean so closed-loop fueling can work. Drivers usually get a check-engine light, fuel trims that freeze or swing oddly, and sometimes a mild surge once the controller gives up on the signal. Freeze frame is often a warm cruise where the O2 PID sits dead, stuck high, or stuck low instead of toggling.

Shop frequency still starts with a failed upstream O2 sensor (open heater sibling codes often ride along), then exhaust leaks ahead of the sensor that suck air and flatten the signal, then chafed harness at the transmission tunnel or heat shield. Next: contaminated probe after silicone or coolant events, connector corrosion, or a shorted signal wire. Rarely the ECM input is bad after the sensor and harness prove clean. Do not throw a converter at P0130—this is the control sensor, not the catalyst monitor sensor.

Diagnosis: graph B1S1 voltage (or equivalence ratio on wideband platforms) at hot idle and cruise; a healthy narrowband toggles roughly across 0.1–0.9 V. Confirm heater power/ground if a heater code is present. Key-off ohm the signal and heater circuits against OEM charts; wiggle the harness while watching for dropouts. Smoke or listen for exhaust leaks at the manifold flange and flex pipe before the sensor. Replace the upstream sensor when wiring and exhaust sealing are good yet the signal stays dead or pegged. Dig elsewhere when a new sensor still flatlines with a manifold gasket leak, when fuel trim evidence points to a large vacuum leak instead, or when only the downstream sensor is lazy (different code family). System context: B1S1 is the closed-loop brain for Bank 1—fix it before you chase P0420 or injector balance.