Emission controls · Powertrain · generic (SAE-defined)
P0157: O2 Sensor Circuit Low Voltage (Bank 2 Sensor 2)
P0157 means the downstream oxygen sensor after the bank 2 catalytic converter is reading lower voltage than expected, as if the exhaust there is always lean.
Standard title per SAE J2012 / ISO 15031-6 · Updated 2026-11-07 · By CarWhere Research
How P0157 sets
The powertrain control module (PCM) watches the bank 2 sensor 2 oxygen (O2) sensor after the catalytic converter, which normally reports a moderately high, steady signal. If the reading stays below its expected range for longer than allowed, even when the PCM enriches the mixture, it stores P0157. Limits are manufacturer-specific.
Common causes of P0157
Roughly most likely first; the actual cause depends on the vehicle and needs testing to confirm.
- Exhaust leak ahead of the bank 2 downstream sensor
- Failed bank 2 sensor 2 oxygen sensor
- Signal wire grounded against the body or exhaust
- Damaged connector or wiring
- Lean running on bank 2
P0157 symptoms
- Check engine light on
- Usually no drivability symptoms
- Possible exhaust ticking or puffing sound from a leak
How P0157 is diagnosed
- Scan for codes; lean codes like P0174 suggest an engine-side cause.
- Inspect the bank 2 exhaust from manifold to downstream sensor for leaks.
- Inspect the sensor harness for grounding or damage.
- On live data, add fuel briefly and confirm the sensor rises.
- Unplug the sensor and test the signal wire for a short to ground.
Typical fixes for P0157
- Repair exhaust leaks before the sensor
- Replace the bank 2 sensor 2 oxygen sensor
- Repair grounded or damaged wiring
Replace parts only after testing confirms the cause — a code names the circuit or condition that failed a check, not necessarily the faulty part. We don’t publish per-repair prices; for what households actually spend on upkeep, see car repair costs.
Related codes & warning lights
P0157 FAQ
What does code P0157 mean?
P0157 means the downstream oxygen sensor after the bank 2 catalytic converter is reading lower voltage than expected, as if the exhaust there is always lean. The standard definition is "O2 Sensor Circuit Low Voltage (Bank 2 Sensor 2)."
Can I drive with a P0157 code?
Yes, the engine usually runs normally. Repair it before an emissions inspection, and look for exhaust leaks that could also be noisy.
Does P0157 mean I need a catalytic converter?
No. P0157 concerns the sensor signal. Converter problems are reported with efficiency codes such as P0430.
Can a cracked exhaust pipe cause P0157?
Yes. A crack or loose joint upstream of the sensor can draw in outside air, which lowers the sensor reading.
Keep researching
More emission controls codes
Sources
- SAE J2012 — Diagnostic Trouble Code Definitions (standard code titles)
- ISO 15031-6 — Road vehicles: communication between vehicle and external equipment for emissions-related diagnostics, Part 6: Diagnostic trouble code definitions
- U.S. EPA — Vehicle Emissions Inspection and Maintenance (I/M) programs
- U.S. EPA, 40 CFR 86.1806-17 — Federal onboard diagnostics requirements for light-duty vehicles
- California Air Resources Board — On-Board Diagnostic (OBD) Program
General information written by CarWhere Research, not a diagnosis of your vehicle. Manufacturers can add their own sub-definitions and test conditions; confirm with the factory service information for your year, make and model. Before paying for a repair, check NHTSA for open recalls and your warranty booklet: federal law requires an emissions warranty on major emission-control parts such as the catalytic converter and engine computer.