P0131
O2 Sensor Low Voltage (Bank 1 Sensor 1)
medium
i Description
The upstream O2 sensor on Bank 1 is consistently reading a low voltage (below 0.2V), indicating a lean exhaust condition or a faulty sensor stuck lean.
? Common Causes
- Vacuum leak
- Low fuel pressure
- Faulty O2 sensor
- Exhaust leak before the sensor
- Faulty MAF sensor reading low
! Symptoms
- Check engine light
- Lean running condition
- Hesitation
- Poor fuel economy
# Diagnostic Steps
- Check for vacuum leaks
- Test fuel pressure
- Monitor O2 sensor signal (should not stay permanently low)
- Check for exhaust leaks
- Inspect MAF sensor
⚙ Typical Fix
Repair vacuum or exhaust leaks, or replace the O2 sensor if it is stuck lean.
Parts Needed
O2 sensor, Vacuum hoses (if leaking)
Estimated Cost
$100-$400
↔ Related Codes
Q Frequently Asked Questions
Yes, but a lean condition can cause engine damage if severe. Monitor for misfires and address promptly.
☞ Learn More
- Check Engine Light — What it means, is it safe to drive & how to fix
- What is OBD-II? — Complete guide to your car's diagnostic system
- How to Read DTC Codes — Step-by-step with a Bluetooth scanner
- OBD-II Scanner Buying Guide — Find the best scanner for your car