What it means
The reference voltage on the bank 1, sensor 1 wide-band oxygen sensor reads above the upper threshold. Common with a short to a positive supply or a corroded connector with leakage current.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The upstream wide-band oxygen sensor on bank 1 uses a reference voltage in its exhaust measurement, and the engine control module monitors that feed at Sensor 1. This code sets when the reference circuit rises above its expected range, which can happen if it contacts a positive supply or has leakage across a corroded connector.
Common causes
Most likely first.
- Reference line shorted to positive
- Connector corroded with leakage
- Supply wire pinched against B+ source
Symptoms
- Check engine light on
- Increased fuel consumption
- Possible rough idle or hesitation
- Failed emissions test
How to diagnose it
- Save freeze-frame data and inspect Bank 1 Sensor 1 live data for a reference reading that remains high or changes with vibration.
- Check the Bank 1 Sensor 1 connector for corrosion or moisture and inspect the harness for pinched insulation or contact with a positive-supply wire.
- Use the wiring diagram to test the reference line for a short to voltage, concentrating on rubbed or trapped sections of the harness.
- Check connector pins for contamination and leakage paths, and verify circuit continuity against the manufacturer's specification.
- If the wiring and connector pass, test the sensor and module reference output separately using the manufacturer's procedure.
Common fixes
- Repair a pinched or chafed reference wire contacting a positive supply.
- Clean or replace corroded Bank 1 Sensor 1 connector terminals.
- Replace the sensor if testing confirms an internal fault affecting the reference circuit.
- Repair the module output only if testing isolates the fault to the module.
Can I keep driving?
You may be able to drive cautiously, but fuel economy and engine smoothness can deteriorate as the module loses a reliable bank 1 mixture reading. Limit driving if rough running or hesitation develops, and resolve the fault before emissions testing.
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.