Faulty Bank 2 Sensor 2 oxygen sensor, possibly contaminated with fuel or coolant (all three sources treat a bad sensor as the most common cause). Exhaust leak ahead of the sensor letting in outside air and giving a false lean reading (OBD-Codes.com, KBB). Engine actually running lean, usually with lean codes P0171 or P0174 also set (OBD-Codes.com). Signal circuit shorted to ground, an open ground circuit, or a damaged or corroded connector (OBD-Codes.com); KBB also lists corroded or damaged wiring. Fuel pressure too high or too low, and battery voltage problems (KBB only). Oxygen sensor heater not getting power or ground (OBD-Codes.com, usually with its own heater code). Less often, a failed PCM (OBD-Codes.com).

Replace the Bank 2 Sensor 2 oxygen sensor if testing shows it's faulty. Repair exhaust leaks ahead of the sensor. Repair a signal wire shorted to ground, an open ground, or a damaged connector. Fix the cause of a lean condition (vacuum leaks, fuel pressure) if the engine really is running lean. Restore power or ground to the sensor heater, or replace the sensor if its heater element has failed.

P0157🌫 Emissions / oxygen sensorsDrive with caution, fix soon

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

Q: What does P0157 mean?

P0157 means the downstream oxygen sensor (after the catalytic converter) on Bank 2 is reporting a voltage that stays too low for too long. A failed sensor is the most common cause; exhaust leaks ahead of the sensor, a lean-running engine and wiring shorted to ground are the next things to check. It usually does not mean the catalytic converter is bad. Sensor 2 is the downstream oxygen sensor, mounted after the catalytic converter. Bank 2 is the side of a V6, V8 or flat engine that does not have cylinder #1, so P0157 only appears on engines with two banks. The engine computer (PCM) compares this rear sensor with the front one to judge how well the catalytic converter is working. OBD-Codes.com explains that a healthy rear sensor moves slowly, a little above and below about 0.45 volts, and a low reading means the exhaust looks lean (high in oxygen). The code sets when the voltage stays below the PCM's threshold for too long. KBB puts that at about 20 seconds; OBD-Codes.com says the exact threshold depends on the vehicle. OBD-Codes.com also stresses that P0157 usually does not mean the catalytic converter is bad. P0158 is the matching high-voltage code for the same sensor, and P0137 is the low-voltage code for the Bank 1 rear sensor.

Q: Can I keep driving with P0157?

Drive with caution, fix soon. Usually drivable, but don't ignore it. RepairPal rates it Moderate: not an immediate safety threat, but get it diagnosed within a reasonable time. OBD-Codes.com says a rear oxygen sensor problem usually won't cause drivability issues on its own. KBB is more cautious: you can usually drive to a shop, but if the engine's air-fuel ratio really is off, driving for a long time can damage the engine. An open code can also fail an OBD2 emissions inspection.

Reviewed 2026-10-22 · Based on 3 cited source(s)

What P0157 means

Sensor 2 is the downstream oxygen sensor, mounted after the catalytic converter. Bank 2 is the side of a V6, V8 or flat engine that does not have cylinder #1, so P0157 only appears on engines with two banks. The engine computer (PCM) compares this rear sensor with the front one to judge how well the catalytic converter is working. OBD-Codes.com explains that a healthy rear sensor moves slowly, a little above and below about 0.45 volts, and a low reading means the exhaust looks lean (high in oxygen). The code sets when the voltage stays below the PCM's threshold for too long. KBB puts that at about 20 seconds; OBD-Codes.com says the exact threshold depends on the vehicle. OBD-Codes.com also stresses that P0157 usually does not mean the catalytic converter is bad. P0158 is the matching high-voltage code for the same sensor, and P0137 is the low-voltage code for the Bank 1 rear sensor.

Severity: can I keep driving?

Drive with caution, fix soon

Usually drivable, but don't ignore it. RepairPal rates it Moderate: not an immediate safety threat, but get it diagnosed within a reasonable time. OBD-Codes.com says a rear oxygen sensor problem usually won't cause drivability issues on its own. KBB is more cautious: you can usually drive to a shop, but if the engine's air-fuel ratio really is off, driving for a long time can damage the engine. An open code can also fail an OBD2 emissions inspection.

Common symptoms

Check engine light on (KBB and OBD-Codes.com say this may be the only sign)
Rough idle or rough running (OBD-Codes.com, KBB)
Lower fuel economy and an exhaust odor (KBB)
Engine performance issues, mostly when other codes such as lean or front-sensor codes are also set (OBD-Codes.com)
May fail an OBD2 emissions inspection

Likely causes

Roughly most to least common, based on the sources below. Your vehicle may differ.

Faulty Bank 2 Sensor 2 oxygen sensor, possibly contaminated with fuel or coolant (all three sources treat a bad sensor as the most common cause)
Exhaust leak ahead of the sensor letting in outside air and giving a false lean reading (OBD-Codes.com, KBB)
Engine actually running lean, usually with lean codes P0171 or P0174 also set (OBD-Codes.com)
Signal circuit shorted to ground, an open ground circuit, or a damaged or corroded connector (OBD-Codes.com); KBB also lists corroded or damaged wiring
Fuel pressure too high or too low, and battery voltage problems (KBB only)
Oxygen sensor heater not getting power or ground (OBD-Codes.com, usually with its own heater code)
Less often, a failed PCM (OBD-Codes.com)

Diagnostic steps you can do

⚠ Before you start

Work on a cool engine, parked on level ground with the parking brake set. Never work under a car supported only by a jack.

Read all stored codes. If lean codes (P0171, P0174) or front-sensor codes are also set, fix those first, then clear the codes and see whether P0157 returns.
Look and listen for exhaust leaks at the manifold and pipes ahead of the Bank 2 rear sensor, and fix them first.
Find the Bank 2 Sensor 2 sensor (after the catalytic converter on the side without cylinder #1) and inspect its connector and wiring for corrosion, moisture, damaged pins, or wires touching the exhaust.
With a scan tool that shows live data, watch the Bank 2 Sensor 2 voltage on a warm engine (a fast idle may help). A reading stuck low while there are no other oxygen sensor codes points to the sensor; a reading that only drops now and then often still turns out to be the sensor, per OBD-Codes.com.
Clear the code and drive normally to see whether it comes back.

Typical fixes

Replace the Bank 2 Sensor 2 oxygen sensor if testing shows it's faulty
Repair exhaust leaks ahead of the sensor
Repair a signal wire shorted to ground, an open ground, or a damaged connector
Fix the cause of a lean condition (vacuum leaks, fuel pressure) if the engine really is running lean
Restore power or ground to the sensor heater, or replace the sensor if its heater element has failed

Repair costs vary widely by vehicle, region, parts brand and shop, so we don't quote prices. Get a written estimate after diagnosis.

🛠 When to call a pro

You want to confirm a wiring fault before buying a sensor: OBD-Codes.com's test involves unplugging the sensor, checking heater power and ground, and jumping the PCM-side ground circuit, which needs a wiring diagram
The code returns after a new sensor (OBD-Codes.com's forums have many such cases)
You need a fuel-pressure test
The engine runs rough or you suspect the air-fuel ratio really is off (KBB warns this can lead to engine damage)

Where to buy

Plain search links. Always match parts to your exact year, make, model and engine.

OBD2 scanners on Amazon Parts at Advance Auto Parts catalog at RockAuto

FAQs

Is P0157 serious?

Usually not an emergency. RepairPal rates it Moderate, and OBD-Codes.com says rear oxygen sensor problems usually don't affect how the car drives. KBB is more cautious and says long-term driving with a real air-fuel problem can damage the engine, so get it checked soon.

Does P0157 mean my catalytic converter is bad?

Usually not. OBD-Codes.com says P0157 almost never means the converter has failed; it's about the rear sensor's signal being too low.

Where is Bank 2 Sensor 2?

Bank 2 is the side of the engine opposite cylinder #1, and Sensor 2 is the oxygen sensor after the catalytic converter on that side. Check your service manual or a parts catalog for your engine, since the side varies.

Will a new oxygen sensor fix P0157?

Often, since all three sources point to a failed sensor as the most common cause. But exhaust leaks, a lean-running engine or a wire shorted to ground set the same code, so check those first if you want to avoid buying a sensor you don't need.

Why do the sources list different causes?

KBB alone mentions fuel pressure that's too high or too low and battery voltage problems; OBD-Codes.com alone mentions a lean-running engine, heater circuit problems and PCM failure. RepairPal only says the PCM detected a failure of the sensor or its signal. They all agree on a faulty sensor, and KBB and OBD-Codes.com both list wiring and exhaust leaks.

Sources

Last reviewed 2026-10-22. Code definitions and repair steps can vary by manufacturer. Confirm with your vehicle's service information.