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DTC code page

P0157: O2 Sensor Circuit Low Voltage (Bank 2 Sensor 2)

Quick answer: The downstream oxygen sensor on Bank 2 is stuck too low or is reporting a low-voltage signal the ECU does not trust.

Drivers also search this fault as bank 2 sensor 2 low voltage, rear O2 low voltage bank 2, downstream oxygen sensor lean signal bank 2.

Severity: low Family: powertrain Related paths: 11
Meaning

What P0157 usually means

P0157 is the Bank 2 counterpart to P0137. It says the Bank 2 rear oxygen-sensor signal is staying lower than expected. That can happen because the sensor is biased lean, the circuit has resistance or ground trouble, or a leak is pulling outside oxygen into the exhaust stream near the sensor. In practice the code often matters because it distorts Bank 2 catalyst conclusions, not because it causes dramatic drivability on its own.

Fast triage

Start here before chasing parts

  • Scan first: save freeze-frame and pending codes before clearing anything.
  • Confirm the complaint: compare the stored code with current drivability symptoms.
  • Use context: trims, live data, and related codes usually narrow the fault faster than guesswork.
  • Work simplest to hardest: leaks, connectors, maintenance items, and known patterns before expensive components.
Initial checks

What to check first

  • Inspect for exhaust leaks on the Bank 2 side before replacing the sensor immediately.
  • Check the Bank 2 Sensor 2 connector and wiring for heat damage or terminal corrosion.
  • If P0430 is present, do not treat low downstream voltage as automatic proof of a failed converter.
Driving risk

Can you keep driving?

P0157 usually is not urgent, but it can mislead Bank 2 catalyst diagnosis and delay emissions-readiness completion until the real cause is fixed.

Moderate urgency: This code often allows short-term driving, but the right fix usually comes faster when you diagnose it early instead of waiting for more codes.
Likely causes

Common causes behind this code

  • Downstream oxygen sensor on Bank 2 biased low or failing internally
  • Signal-circuit resistance, poor ground, or connector corrosion
  • Exhaust leak on the Bank 2 rear-sensor side
  • Harness damage from heat, road debris, or previous repair work
  • Catalyst-monitor context that still needs to be separated from a true sensor failure

Cause phrases often tied to this code: rear O2 sensor stuck lean bank 2, signal low voltage, exhaust leak, wiring resistance, connector problem.

Diagnostic order

Suggested workflow

  1. Verify the correct Bank 2 rear-sensor location and inspect the harness physically.
  2. Review live downstream O2 data and confirm the signal is actually biased or stuck low.
  3. Inspect the exhaust path near the rear sensor and catalyst outlet for leaks or disturbed joints.
  4. Check signal and ground integrity before replacing the sensor.
  5. After repair, verify the Bank 2 rear-sensor data recovers and catalyst-monitor logic looks cleaner.
Avoid guesswork

Common mistakes

  • Replacing the converter without proving the rear sensor and exhaust path are believable first.
  • Skipping leak inspection because the code mentions voltage.
  • Confusing Bank 2 Sensor 2 with Bank 2 Sensor 1 during testing.
Repair path

Practical fix guidance

  • Fix exhaust leaks, connector damage, or poor grounds before replacing the sensor if those are present.
  • Replace the Bank 2 downstream sensor when it is proven stuck low or electrically compromised.
  • Recheck P0430-style companion logic after repair rather than assuming the rear sensor solved every monitor problem.
Vehicle context

Affected brands in this MVP

Brand hubs help broaden internal linking now and can evolve into make-specific diagnostic notes later.

Aliases and common searches

English phrases tied to P0157

Useful when the driver knows the wording but not the exact DTC yet.

  • bank 2 sensor 2 low voltage
  • rear O2 low voltage bank 2
  • downstream oxygen sensor lean signal bank 2
Related search intent

Queries this page can answer naturally

  • P0157 code meaning
  • what does P0157 mean
  • O2 sensor low voltage bank 2 sensor 2
  • rear O2 sensor stuck low bank 2
FAQ

Quick questions about P0157

Does P0157 mean Bank 2 is truly lean?

Not necessarily. This is a downstream sensor low-voltage code, so sensor, circuit, or exhaust issues can all create the low reading.

Can an exhaust leak cause P0157?

Yes. Fresh air reaching the Bank 2 rear sensor can make its voltage look artificially low.

Is P0157 just the Bank 2 version of P0137?

Yes. Both are rear oxygen-sensor low-voltage codes, but on different banks.