O2 Sensor Reference Voltage Circuit/Open Bank 1 Sensor 1
Diagnostic trouble code P2243 indicates that the engine control module (ECM) has detected an open circuit or improper voltage in the reference voltage circuit for the upstream oxygen sensor on Bank 1. The ECM sets this code when it cannot establish the baseline voltage needed to accurately read the sensor's air/fuel ratio data.
While the vehicle will typically still drive, the engine will default to a less efficient open-loop fuel strategy. This should be diagnosed soon to prevent poor fuel economy, drivability issues, and potential long-term damage to the catalytic converter.
Common symptoms
- Illuminated Check Engine Light
- Decreased fuel economy
- Rough idle or engine hesitation
- Strong fuel odor from the exhaust
- Failed emissions test
Likely causes
- Faulty Bank 1 Sensor 1 oxygen (O2) or air/fuel ratio sensor
- Damaged, melted, or frayed wiring in the O2 sensor harness
- Corroded, loose, or disconnected O2 sensor electrical connector
- Open circuit in the reference voltage wire between the PCM and the sensor
- Internal fault in the Powertrain Control Module (PCM)
What to check before replacing parts
Visually inspect the Bank 1 Sensor 1 O2 sensor wiring and connector.
Look for: Look for melted wires from exhaust heat, chafing, or corrosion inside the connector pins.
Check the reference voltage at the O2 sensor connector with the key on, engine off.
Look for: Using a multimeter, verify that the reference voltage (typically 5 volts, depending on the manufacturer) is present at the harness side of the connector.
Test the ground circuit at the O2 sensor connector.
Look for: Ensure there is a solid ground connection with low resistance to the chassis or PCM ground.
Perform a continuity test on the reference voltage wire between the sensor connector and the PCM.
Look for: A reading of infinite resistance (OL) indicates an open circuit or broken wire in the harness that needs repair.
Test the O2 sensor internal resistance if the wiring is intact.
Look for: Compare the sensor's internal resistance to factory specifications; an open internal circuit means the sensor must be replaced.
This page explains the generic P2243 definition and is general reference information, not a diagnosis for your specific vehicle. Actual causes, severity, and repairs vary by make, model, engine, and mileage — always confirm with a scan tool and a qualified technician before replacing parts.
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