O2 Sensor Reference Voltage Circuit Low Bank 2 Sensor 1
The P2249 code indicates that the Engine Control Module (ECM) has detected a low voltage condition in the reference voltage circuit for the oxygen sensor located on Bank 2, Sensor 1 (upstream of the catalytic converter). This reference voltage is typically 5 volts and is used by the sensor to operate. A low voltage can be caused by a faulty oxygen sensor, damaged wiring, poor electrical connections, or a short to ground. This condition can lead to incorrect air-fuel ratio readings, affecting engine performance and emissions.
01. Most Common Causes
- Faulty oxygen sensor (Bank 2 Sensor 1)
- Damaged or corroded wiring/connectors in the sensor circuit
- Short to ground in the reference voltage wire
- ECM internal fault (rare)
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Poor fuel economy
- Rough idle or hesitation during acceleration
- Failed emissions test
03. Step-by-Step Diagnosis
Step 1: Use an OBD2 scanner to confirm the code and check for other related codes.
Step 2: Visually inspect the wiring and connector for Bank 2 Sensor 1 for damage, corrosion, or loose connections.
Step 3: Measure the reference voltage at the sensor connector with a multimeter (should be ~5V with key on engine off). If low, check for shorts or opens in the circuit.
Step 4: If voltage is correct, test the sensor's heater circuit and signal output. Replace the sensor if faulty.
Step 5: Clear the code and test drive to see if it returns. If it does, further diagnose the ECM or wiring.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances as it can cause poor fuel economy, drivability issues, and potential damage to the catalytic converter over time.
How much does it cost to fix?▼
The cost typically ranges from $150 to $300, including parts (oxygen sensor) and labor. DIY replacement can be cheaper if you have the tools.