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DTC code page

P0137: O2 Sensor Circuit Low Voltage (Bank 1 Sensor 2)

Quick answer: The downstream oxygen sensor on Bank 1 is stuck too low or is reporting a low-voltage signal the ECU does not trust.

Drivers also search this fault as bank 1 sensor 2 low voltage, rear O2 low voltage bank 1, downstream oxygen sensor lean signal bank 1.

Severity: low Family: powertrain Related paths: 11
Meaning

What P0137 usually means

P0137 means the Bank 1 rear oxygen sensor signal is reading lower than expected. On many vehicles that can mean the sensor is biased lean, the circuit has high resistance or a ground-side problem, or outside air is reaching the exhaust stream and making the rear sensor look leaner than reality. Because this is a downstream sensor, the code often overlaps with catalyst-monitor confusion more than obvious drivability trouble.

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 before and around the rear sensor, especially if there is a cold-start tick or recent exhaust work.
  • Check the Bank 1 Sensor 2 connector and wiring for corrosion, stretch, or heat damage.
  • If P0420 is present too, do not assume low downstream voltage proves the converter failed.
Driving risk

Can you keep driving?

P0137 usually is not an emergency, but rear-sensor low-voltage faults can mislead catalyst diagnosis and keep emissions monitors from completing correctly.

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 1 biased low or failing internally
  • Signal-circuit resistance, poor ground, or connector corrosion
  • Exhaust leak pulling outside air into the rear-sensor area
  • Rear sensor wiring damaged by heat, road debris, or previous exhaust work
  • Catalyst or exhaust conditions that need to be separated from a true sensor fault

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

Diagnostic order

Suggested workflow

  1. Confirm the correct rear-sensor location and inspect the harness physically.
  2. Review live downstream O2 behavior and confirm the signal is genuinely stuck or biased low.
  3. Inspect the exhaust path for leaks that can dilute the rear-sensor reading with outside oxygen.
  4. Check circuit integrity and ground quality before replacing the sensor.
  5. After repair, verify the downstream signal recovers and catalyst-monitor results make more sense.
Avoid guesswork

Common mistakes

  • Judging the converter first without proving the rear sensor and exhaust path are telling the truth.
  • Skipping exhaust-leak inspection because the code sounds electrical.
  • Replacing the wrong sensor by confusing the rear sensor with Bank 1 Sensor 1.
Repair path

Practical fix guidance

  • Fix exhaust leaks, connector damage, or poor grounds before replacing the sensor if those faults are present.
  • Replace the Bank 1 downstream sensor when it is proven stuck low or electrically compromised.
  • Recheck catalyst and readiness behavior after the repair so a second issue is not left behind.
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 P0137

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

  • bank 1 sensor 2 low voltage
  • rear O2 low voltage bank 1
  • downstream oxygen sensor lean signal bank 1
Related search intent

Queries this page can answer naturally

  • P0137 code meaning
  • what does P0137 mean
  • O2 sensor low voltage bank 1 sensor 2
  • rear O2 sensor stuck low
FAQ

Quick questions about P0137

Does P0137 mean the engine is truly running lean?

Not necessarily. This is a downstream sensor code, so a low rear-sensor signal can come from sensor or exhaust issues as well as actual exhaust chemistry.

Can an exhaust leak cause P0137?

Yes. Fresh air entering near the rear sensor can make the downstream reading look artificially low.

Is P0137 the same as P0171?

No. P0171 is a system-lean code tied more directly to mixture control, while P0137 is a rear oxygen-sensor low-voltage code.