Parts
$30–80
P0137 — O2 Sensor Low Voltage — Bank 1, Sensor 2
SAFEIs it safe to drive? Safe to drive — this is a downstream (post-catalyst) sensor and its failure doesn't directly affect fueling, but it prevents the ECU from confirming catalyst health.
What P0137 means
The downstream O2 sensor on Bank 1 (after the catalytic converter) is reading below 0.1V continuously. It may see a lean signal constantly, or its signal circuit may be open.
Most likely causes (in order)
- Failed downstream O2 sensor ($30–80)
- Exhaust leak between the catalyst and the sensor pulling in fresh air
- Open signal circuit or bad ground at the sensor
- Catalytic converter failed and passing through lean exhaust — sensor is actually reading correctly in this case
- Oil or coolant contamination on the sensor tip
Symptoms you might notice
- Check engine light on
- Possible emissions test failure
- No driveability symptoms in most cases
What to check first
If this code appears alongside P0420 (catalyst efficiency below threshold), the downstream sensor may actually be reading correctly and the catalyst is the real problem — don't replace the sensor until you rule out a bad catalytic converter. Check for exhaust leaks between the cat and the sensor bung first.
Repair cost & difficulty
Labor
0.3–0.7 hr
Difficulty
DIY-friendly