What it means
The reference voltage feeding the bank 1, sensor 1 wide-band oxygen sensor is below the lower threshold. Often a short to ground in the wiring or a failed reference output stage.
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 relies on a reference voltage, and the engine control module monitors that feed at Sensor 1. This code sets when the reference voltage falls below its expected range, commonly because the wire is shorted to ground, a connection has high resistance, or the module output is faulty.
Common causes
Most likely first.
- Reference line shorted to ground
- ECU reference output failed
- Connector pins corroded - high contact resistance
Symptoms
- Check engine light on
- Increased fuel consumption
- Possible rough idle or hesitation
- Failed emissions test
How to diagnose it
- Record freeze-frame data and check Bank 1 Sensor 1 live data to determine whether the low reference condition is present continuously.
- Inspect the Bank 1 Sensor 1 connector for corrosion or loose pins and the harness for crushed or rubbed-through insulation.
- With the wiring diagram, check the reference line for a short to ground and examine likely chafe points near the sensor and engine.
- Measure connector contact quality and reference-circuit continuity against the manufacturer's specification before testing the module.
- If the wiring and connector pass, test the module reference output and the sensor according to the manufacturer's procedure.
Common fixes
- Clean or repair corroded Bank 1 Sensor 1 connector pins.
- Repair a reference wire shorted to ground or damaged by chafing.
- Replace the sensor if it fails the specified test and is pulling the circuit low.
- Repair the module reference output if testing confirms its failure.
Can I keep driving?
The vehicle may be drivable, but the engine can use less accurate mixture feedback, increasing fuel use or causing a rough idle. Avoid continued driving if it hesitates or runs poorly, and fix 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.