P0157: O2 Sensor Circuit Low Voltage Bank 2 Sensor 2
A generic powertrain (engine and transmission) trouble code, same meaning on every brand.
Yes - this is a monitoring sensor, not a fuelling one.
Symptoms
- Check engine light only
- Emissions test failure
- No driveability change
Likely causes, most common first
- Bank 2 downstream sensor signal shorted to ground
- Wiring chafed against the underbody
- Failed sensor
- Water in the connector
Read P0157 yourself before paying for diagnosis
A basic Bluetooth OBD-II scanner ($20-40) plugs into the port under the dashboard and shows this code with live sensor data on your phone - useful both for confirming the fix and for talking to a shop from an informed position.
What is going on and how it gets diagnosed
P0157 is a low-voltage fault on the bank 2 post-catalyst sensor. Because it does not control fuelling, the car drives normally and the only practical consequences are the warning light and a failed emissions test.
The underbody harness is the place to look. Rear sensor wiring runs along the floor where road salt, spray and stones reach it, and connectors that sit in a natural water trap corrode from the inside. A green or crusty terminal found there explains the code and costs far less than a sensor.
Repair options and cost
Typical US independent-shop ranges, parts and labor. Dealers run higher; regional labor rates vary.
Cars that report P0157 most often
Based on mentions of this code in NHTSA owner complaints.
Frequently asked questions
Can I drive with P0157?
Yes - this is a monitoring sensor, not a fuelling one.
How much does it cost to fix P0157?
Typical US repair costs range from $60 for the simplest fix (downstream oxygen sensor) to $400 in the worst case. The right number depends on which cause your car has - see the causes list.
Related codes
The codes closest to P0157. They often appear together, and telling them apart is usually what narrows the diagnosis.
Definition per SAE J2012 standard nomenclature. Symptoms, causes and costs are editorial guidance - always confirm with a diagnosis of your specific vehicle.