What it means
Voltage on the intake air oxygen sensor signal line on bank 1 is below the expected window. A drifted or sluggish lambda sensor lets the mixture run lean or rich without correction — fuel economy and emissions suffer immediately.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The Bank 1 intake-air oxygen sensor sends its oxygen reading to the control module through a signal wire. This code sets when that signal voltage falls below the expected range, often because the wire is grounded, the sensor is internally shorted, or a corroded connector disrupts the circuit.
Common causes
Most likely first.
- Signal wire shorted to ground
- Internal sensor short
- 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
- Capture freeze-frame data and check whether the Bank 1 sensor signal is stuck low or changes with operating conditions.
- Inspect the Bank 1 sensor harness for rubbed-through insulation, especially where it could contact ground, and check the connector for corrosion or displaced pins.
- Compare the Bank 1 signal with other available sensor or mixture readings to confirm that the low value is specific to this circuit.
- With the wiring diagram, test the signal wire for a short to ground and check connector continuity using the manufacturer's procedure.
- If the harness and connector pass, test the Bank 1 sensor itself for an internal short before replacing it.
Common fixes
- Clean and secure corroded or loose Bank 1 sensor connector terminals.
- Repair the Bank 1 signal wire where it is shorted to ground or damaged.
- Replace the Bank 1 intake-air oxygen sensor if testing confirms an internal short.
- Clear the code and verify that the Bank 1 signal responds normally after repair.
Can I keep driving?
If the engine runs smoothly, a short drive to arrange diagnosis is usually reasonable, but avoid hard acceleration if it hesitates or runs roughly. Persistent incorrect mixture control can raise fuel use and emissions and may harm the catalytic converter.
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.