| DTC Data Sheet | |
| System | Powertrain |
| Standard | SAE J2012 / ISO 15031-6 |
| Fault type | Circuit Low |
| Official meaning | O2 Sensor Circuit Low Voltage (Bank 2, Sensor 2) |
Bank 2 downstream O2 sensor signal is stuck low — either lean exhaust passing through a degraded catalyst or a sensor reporting low.
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P0157 Quick Answer
Bank 2 downstream O2 sensor signal is stuck low — either lean exhaust passing through a degraded catalyst or a sensor reporting low.
What Does P0157 Mean?
O2 Sensor Circuit Low Voltage (Bank 2, Sensor 2). Bank 2 downstream O2 sensor signal is stuck low — either lean exhaust passing through a degraded catalyst or a sensor reporting low.
Symptoms
- Check engine light
- May co-code with P0430 (catalyst efficiency)
- Failed emissions test
Common Causes
- Degraded bank 2 catalytic converter (passing lean exhaust through)
- Bank 2 exhaust leak between or after the upstream sensor
- Failed downstream O2 sensor
- Short to ground on the signal wire
Diagnosis Steps
You’ll need a scan tool capable of reading live powertrain data, a digital multimeter, and access to the wiring diagram for the specific platform.
- Read bank 2 downstream voltage during cruise. A healthy catalyst keeps the downstream signal near-flat at 0.6–0.8 V; a degraded catalyst lets the downstream signal mirror the upstream.
- Inspect bank 2 exhaust for leaks.
- Swap the sensor if circuit and exhaust check out.
Possible Fixes
- Bank 2 catalytic converter replacement
- Exhaust leak repair
- Downstream O2 sensor replacement
Can I Still Drive With P0157?
The vehicle will usually still drive with P0157 stored, but performance, drivability, or emissions will be degraded. The PCM may inhibit emissions monitors and limit closed-loop fueling adjustments. Drive to a workshop, but don’t ignore the code long-term — degraded sensor data can mask other faults and shorten catalyst life.
How Serious Is This Code?
P0157 is a moderate-priority fault. It will not prevent the engine from running but unaddressed it can damage the catalytic converter, reduce fuel economy, or cause failed emissions testing. Address within a few drive cycles.
Brand-Specific Guides for P0157
Manufacturer-specific diagnostic procedures with factory data and pin-level details for vehicles where this code commonly sets:
FAQ
Will P0157 clear itself?
Only if the underlying fault was intermittent and self-corrected. Most root causes are persistent and require physical repair.
Can I clear P0157 without fixing it?
You can clear it with a scan tool, but it will return as soon as the fault condition reappears — typically within one or two drive cycles.
Is P0157 related to other codes?
Often, yes. Adjacent codes in the same circuit or system frequently set together — if P0157 is present, scan for related codes and address them as a group.