P0157: O2 Sensor Circuit Low Voltage (Bank 2, Sensor 2)

P0157 is a emissions-related diagnostic trouble code classified as moderate severity. When your vehicle's ECU detects this condition, it stores P0157 and illuminates the check engine light.

If your vehicle has triggered P0157, you may notice one or more of these symptoms:

• Check engine light illuminated
• Slight increase in fuel consumption
• Usually no noticeable change in how the car drives
• Possible failed emissions test
• Often appears alongside P0430 if the bank 2 converter is degrading
• May appear with P0174 if bank 2 is genuinely running lean

Here are the most common causes of P0157:

Generally yes, for short-term driving. Safe to drive short term. The downstream sensor does not directly control fuel mixture, but a persistent low signal often points to a damaged sensor, an exhaust leak or a degrading catalytic converter on bank 2. Do not delay repairs beyond a few weeks.

Follow these steps to pinpoint the root cause of P0157:

1. Confirm which sensor the code means before buying parts: Bank 2 is the cylinder bank that does not contain cylinder 1, and Sensor 2 is the one after the catalytic converter. Check the cylinder numbering for your engine in the service information, because the side of the car bank 2 sits on is not the same on every engine
2. Read freeze frame data and check for companion codes (P0430, P0174, P0171) that suggest a converter problem or a lean condition
3. Inspect the bank 2 exhaust between the catalytic converter and the downstream sensor for cracks, loose clamps or leaking gaskets. A ticking sound on a cold start often gives a leak away
4. Inspect the Bank 2 Sensor 2 connector and wiring for corrosion, heat damage or chafing
5. Use a scan tool to view the downstream sensor voltage. A healthy sensor reads around 0.6-0.8V steady. A reading stuck below 0.2V points to sensor failure or an exhaust leak
6. Compare long-term fuel trim on bank 2 with bank 1. If bank 2 is adding a lot more fuel, that bank is genuinely lean and the sensor may simply be reporting it
7. Substitute a known-good sensor, or swap the bank 1 and bank 2 downstream sensors if they use the same part number. If the low voltage follows the sensor (the code changes to P0137), the sensor is faulty

Repair costs for P0157 vary depending on the root cause and your vehicle. Here are typical estimates:

P0157 behaves differently depending on your vehicle. Select your car below for model-specific causes and known issues:

These codes are often seen alongside P0157 or indicate related issues: