P0157 Code Meaning and Next Steps

First checks take 10 to 15 minutes for the first checks. No special tools are usually needed for the first checks.

Can you keep driving?

Stop driving if any of these apply

!The engine is misfiring, stalling, or the check-engine light starts flashing.
!There is a strong exhaust smell or a drivability change that suggests a bigger fault than the sensor alone.

If the light is steady and the vehicle still drives normally: Often yes for a short time, but it should not be ignored.

What to check first

Step-by-step checks

1
Free - no tools
Inspect the exhaust around the downstream sensor for leaks or loose joints
2
Free - no tools
Check the sensor connector and harness for heat damage or corrosion
3
Basic tool needed
Compare downstream sensor behavior with the upstream signal if scan data is available
4
Basic tool needed
If the vehicle also has catalyst or mixture codes, treat them together
5
Basic tool needed
If the code appeared after exhaust work, inspect the sensor bung and pipe first

If the code returns

-If the exhaust is sealed and the signal is still low, the sensor or wiring becomes more likely.
-If the code returns after a sensor replacement, revisit the leak check before moving on.
-If the signal changes with harness movement, wiring deserves a closer test.

Background

What this code means

P0157 is a generic OBD-II oxygen-sensor code for bank 2 sensor 2.

A low downstream signal can point to an exhaust leak, a sensor that is biased low, or a wiring fault.

Catalyst-monitor behavior may be off even if the vehicle still drives normally.

Diagnosis

Common causes

Most common

Exhaust leak near sensor

Fresh air can pull the downstream reading low.

Common

Failed downstream O2 sensor

The sensor can bias low even without a major exhaust issue.

Common

Connector or wiring issue

Heat damage or poor pins can distort the signal.

Possible

Mixture or catalyst effect

Other engine-running issues can shape the downstream signal.

Avoid these mistakes

What not to do

xDo not replace oxygen sensors first if there is an obvious exhaust leak or mixture problem.
xDo not ignore rough running just because the code names a sensor.

Parts

Parts that may need replacing

PartTypical costNotes

Downstream oxygen sensor$50-$180Relevant when the sensor proves biased low.

Exhaust gasket or leak repair$20-$200Worth checking if a leak is present near the sensor.

Connector pigtail repair$15-$90Relevant if the connector is damaged.

Related OBD codes

P0156

P0156 usually means the bank 2 sensor 2 oxygen sensor circuit is not behaving correctly.

P0158

P0158 usually means the bank 2 sensor 2 oxygen sensor is reading too high.

P0420

P0420 usually means the catalytic converter efficiency is below the threshold the ECU expects.

Source notes

Generic OBD-II (SAE J1979 / ISO 15031-5). P0157 was expanded around common low bank 2 sensor 2 signal faults, including exhaust leaks, sensor bias, and wiring issues.

This guide is written as a generic multi-make reference, so bulletin history, sensor locations, and repair order can still change by manufacturer and engine family.

This is generic OBD-II guidance and should not override vehicle-specific service information. Exact diagnosis and repair steps vary by make, engine family, and model year.

Last reviewed: 2026-04-10

Reference: Open reference

P0157 - P0157 Usually Means the Bank 2 Sensor 2 Oxygen Sensor Is Reading Too Low