OBD-II Code · Sensors
P0157
O2 Sensor Low Voltage (B2S2)
Bank 2 downstream voltage low.
Common symptoms
- CEL
Likely causes
- Failed sensor
- Wiring short
- Lean exhaust
Where to start
- Try the cheapest cause first. Start by checking: failed sensor.
- Cost & scope. $150-$400
- If the code returns after the fix: escalate to a shop or scanner with live-data and freeze-frame. A code that re-sets means the underlying fault is still there.
Read the full diagnostic procedure
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 patterns
Vehicle-specific patterns: 1999-2006 Chevy Silverado / Sierra 5.3L — longitudinal, bank 2 is driver side; throws P0157 from rusted-out driver-side flex pipe. 2005-2010 Honda Odyssey / Pilot J35 — transverse, bank 2 is front; sets P0157 after VCM cylinder-deactivation events erode the front cat. 2007-2014 Toyota Tundra / Sequoia 5.7L 3UR-FE — bank 2 is passenger side; throws P0157 from connector moisture intrusion. 2008-2014 Cadillac 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.
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