Parts
$30–80
P0157 — O2 Sensor Low Voltage — Bank 2, Sensor 2
SAFEIs it safe to drive? Safe to drive — this downstream sensor monitors catalyst health and its failure is an emissions concern, not a driveability or mechanical risk.
What P0157 means
The downstream O2 sensor on Bank 2 is reading a continuously lean (below 0.1V) signal. This prevents the ECU from evaluating catalytic converter efficiency on Bank 2.
Most likely causes (in order)
- Failed downstream O2 sensor ($30–80)
- Exhaust leak between catalytic converter and sensor admitting fresh air
- Open signal circuit or corroded connector
- Catalytic converter failing and passing lean exhaust — verify before replacing the sensor
Symptoms you might notice
- Check engine light on
- Emissions test failure
- No driveability symptoms in most cases
What to check first
If P0430 (Bank 2 catalyst below threshold) is also set, the sensor may be reading accurately and the catalytic converter is failing — do not replace the sensor until the catalyst is ruled out. Inspect for exhaust leaks at the sensor bung and the cat outlet flange first.
Repair cost & difficulty
Labor
0.3–0.7 hr
Difficulty
DIY-friendly