How much does it cost to fix P0157?

DIY repair typically costs $25–$100 for parts. Professional repair runs $140–$350 including parts and labor.

P0157

Powertrain

Low

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

Get Your FREE AI Diagnostic Report

Enter your vehicle for a personalized diagnosis for code P0157

P0157 means the PCM is detecting a persistently low voltage signal from the downstream oxygen sensor on Bank 2. In a normally functioning system, this sensor should oscillate between approximately 0.1 and 0.9 volts as it monitors the catalytic converter's output. A stuck-low reading typically indicates the sensor is reading lean — either because the exhaust truly is lean, or because the sensor itself has failed.

The downstream O2 sensor's primary role is to monitor catalytic converter efficiency rather than directly controlling fuel mixture, so driveability symptoms are often minimal. However, some modern vehicles do use this sensor for fine fuel trim corrections, so you might notice slightly increased fuel consumption or a marginally rougher idle.

The most common repair is replacing the oxygen sensor, which typically costs $25 to $100 for the part. Before replacing it, check for exhaust leaks near the sensor and inspect the wiring harness for damage. An exhaust leak is a common culprit that can be fixed more cheaply than a sensor replacement. If the code returns after sensor replacement, further diagnosis of the wiring circuit or fuel system may be needed.

Severity

Low — MonitorThis Month

Symptoms

•Check Engine Light is on
•Slightly increased fuel consumption
•Engine may run slightly rich
•Mild exhaust odor
•Possible rough idle at startup
•Failed emissions test

Likely Causes

Worn or failed downstream O2 sensor40%

The oxygen sensor on Bank 2 downstream of the catalytic converter has degraded over time and is stuck producing a consistently low voltage signal, indicating a lean exhaust condition.

Wiring short to ground or open circuit25%

The sensor signal wire has a short to ground or an open in the circuit, which pulls the voltage reading abnormally low regardless of actual exhaust conditions.

Exhaust leak before the sensor20%

An exhaust leak upstream of or near the downstream sensor allows ambient air to reach the sensor, diluting exhaust gases and causing a falsely lean (low voltage) reading.

Lean fuel condition on Bank 210%

An actual lean running condition on Bank 2 — from a vacuum leak, weak fuel injector, or low fuel pressure — is causing legitimately low O2 sensor voltage.

Corroded or loose sensor connector5%

Corrosion or a loose fit at the sensor connector creates high resistance in the signal circuit, resulting in a voltage drop that reads as low voltage.