OBD-II Code · Sensors
P0157
O2 Sensor Low Voltage (B2S2)
Severity
low
Lowest on our scale. Fix it when convenient.
Can you drive it
Only if running normally
A short trip to a shop may be reasonable if the light is steady and the car runs normally. Stop safely for a flashing light, severe shaking, overheating, loss of power, or another urgent warning. The code alone cannot confirm safety.
Indicative cost (USD)
$150–$400
Varies by vehicle, diagnosis, parts, and local labor. This is not a repair quote.
Bank 2 downstream voltage low.
How a shop works this
Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed.
Note every code that is set, not just this one.
Codes that appear together usually narrow the cause faster than any one of them read alone.
Read the freeze frame — the conditions the fault was recorded under.
Cold or warm, idle or load, road speed and engine speed. A fault that only appears cold is a different fault from one that only appears under load, even with the same code on the scanner.
Confirm the fault is current rather than history.
Clear the code and see whether it returns under those same conditions. A code that does not come back may have been logged during a repair, a flat battery, or a bad connection that has since been disturbed.
Then work the likely-causes list in the order shown.
That order is what a shop checks first for this code — wiring and connections before the component they run to, because a connector costs nothing to inspect and is a common answer.
If the code comes back after a repair, the underlying fault is still there. That is the point to bring in a scanner with live data and freeze-frame, or a shop that has one.
Common symptoms
- Check engine light
Likely causes
- Failed sensorMost common
- Wiring short
- Lean exhaust
Read the full diagnostic procedureP0157 is bank 2 downstream signal stuck LOW — bank-2 mirror of P0137.
P0157 is bank 2 downstream signal stuck LOW — bank-2 mirror of P0137. Post-cat sensor reading 'lots of oxygen' constantly.
Three possibilities, cheapest-first
- real lean exhaust at the post-cat position (exhaust leak between bank-2 cat and downstream sensor — flex pipe pinhole, cracked weld, leaking gasket); a failed bank-2 cat that no longer consumes oxygen (typically sets P0430 alongside); or a wiring fault pulling the signal to ground.
- Visually + audibly check for exhaust leaks first — pinholes in flex pipe weld zones are extremely common on salt-belt cars.
- If exhaust is sealed and B2S1 upstream is switching normally and bank-2 fuel trims are reasonable, swap B2S2 with a known-good unit before condemning the cat.
Vehicle-specific patterns1999-2006 Chevy Silverado / Sierra 5.3L — longitudinal, bank 2 is driver side; throws P0157 from rusted-out driver-side flex pipe.
- 1999-2006Chevy Silverado / Sierra 5.3L — longitudinal, bank 2 is driver side; throws P0157 from rusted-out driver-side flex pipe.
- 2005-2010Honda Odyssey / Pilot J35 — transverse, bank 2 is front; sets P0157 after VCM cylinder-deactivation events erode the front cat.
- 2007-2014Toyota Tundra / Sequoia 5.7L 3UR-FE — bank 2 is passenger side; throws P0157 from connector moisture intrusion.
- 2008-2014Cadillac CTS / SRX 3.6L LLT direct-injection — transverse, bank 2 is front; sets P0157 from front-bank cat damage caused by carbon-fouling-induced misfires. Cost band: $150-$350 for sensor; $300-$700 if flex-pipe weld is the cause; $1,000+ if cat actually failed.
Look up another code
P0157 — frequently asked
What does a P0157 code mean?
Bank 2 downstream voltage low.
What causes a P0157 code?
Common causes: Failed sensor; Wiring short; Lean exhaust.
What are the symptoms of a P0157 code?
Typical symptoms: Check engine light.
Is it safe to drive with a P0157 code?
Only if running normally. A short trip to a shop may be reasonable if the light is steady and the car runs normally. Stop safely for a flashing light, severe shaking, overheating, loss of power, or another urgent warning. The code alone cannot confirm safety. Estimated repair: $150-$400.
How do I diagnose a P0157 code?
Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed. 1. Note every code that is set, not just this one. 2. Read the freeze frame — the conditions the fault was recorded under. 3. Confirm the fault is current rather than history. 4. Then work the likely-causes list in the order shown.
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