P0137🌫 Emissions / oxygen sensor (downstream, after the catalytic converter)Drive with caution, fix soon

P0137: O2 Sensor Circuit Low Voltage (Bank 1, Sensor 2) (Meaning, Causes, Fixes)

Reviewed 2026-10-22 · Based on 2 cited source(s)

What P0137 means

Most engines have an oxygen sensor before the catalytic converter (sensor 1) and one after it (sensor 2). The rear sensor's main job is to monitor how well the converter is working. A low voltage from an oxygen sensor reads as a lean exhaust (lots of oxygen). OBD-Codes.com describes P0137 as a generic OBD-II code and says it sets when the Bank 1 Sensor 2 voltage stays low for longer than 2 minutes, or when the computer decides the sensor is inactive. RepairPal says it sets when the rear sensor voltage stays below 400 millivolts for more than twenty seconds, or when an air-fuel ratio sensor stays lean-biased for too long, and notes that the exact conditions vary by make and model. The two sources give different time thresholds, so check your vehicle's service information for the exact rule. Bank 1 is the side of the engine with cylinder 1; an inline four or six with a single exhaust has only Bank 1. P0138 is the matching high-voltage code for the same sensor, and P0157 is the low-voltage code for Bank 2, Sensor 2.

Severity: can I keep driving?

Drive with caution, fix soon

Get it diagnosed within a reasonable time. RepairPal rates P0137 Moderate, meaning it may not threaten safety or drivability right away but should still be checked. OBD-Codes.com says there may be no symptoms other than the check engine light. If the engine idles rough, misfires, or the check engine light flashes, keep driving to a minimum and get it looked at sooner.

Common symptoms

Likely causes

Roughly most to least common, based on the sources below. Your vehicle may differ.

  1. Faulty oxygen sensor or air-fuel ratio sensor (OBD-Codes.com, RepairPal)
  2. Exhaust leak, especially near the rear sensor (OBD-Codes.com, RepairPal)
  3. Wiring or circuit problems on the sensor signal circuit, such as a short, an open or high resistance (OBD-Codes.com, RepairPal)
  4. Defective oxygen sensor heater circuit (RepairPal)
  5. Plugged or defective catalytic converter (OBD-Codes.com, RepairPal)
  6. Engine running very rich or lean, including intake air or vacuum leaks (OBD-Codes.com; RepairPal lists intake air and vacuum leaks)
  7. Engine misfire (OBD-Codes.com)
  8. Fuel pressure problems: OBD-Codes.com lists very high or low fuel pressure from the fuel pump or pressure regulator, while RepairPal lists low fuel pressure
  9. Defective engine coolant temperature sensor (RepairPal)
  10. PCM software needing an update, or a failed PCM (RepairPal)

Diagnostic steps you can do

⚠ Before you start

Work on a cool engine, parked on level ground with the parking brake set. Never work under a car supported only by a jack.

  1. Read all stored codes. If misfire, lean (P0171) or fuel pressure codes are also present, deal with those first, since both sources list engine running problems as causes.
  2. Look and listen for exhaust leaks near the rear oxygen sensor, which both sources list as a cause.
  3. Inspect the rear Bank 1 sensor's wiring and connector for damage, melted insulation near the exhaust, or loose pins (both sources list wiring and circuit faults).
  4. Check for intake air or vacuum leaks, such as cracked hoses or a loose intake duct (RepairPal).
  5. Check for technical service bulletins or PCM software updates for your vehicle, since RepairPal lists PCM software as a possible cause.

Typical fixes

Repair costs vary widely by vehicle, region, parts brand and shop, so we don't quote prices. Get a written estimate after diagnosis.

🛠 When to call a pro

  • Testing the sensor signal and heater circuits needs a multimeter or scan tool and the vehicle's wiring diagram
  • Fuel pressure testing is needed to rule out a weak fuel pump or regulator
  • A restricted catalytic converter is suspected, which is an expensive part worth confirming first
  • The code comes back after replacing the sensor and checking the wiring

Where to buy

Plain search links. Always match parts to your exact year, make, model and engine.

OBD2 scanners on Amazon Parts at Advance Auto Parts catalog at RockAuto

FAQs

Is P0137 serious?

RepairPal rates it Moderate. OBD-Codes.com says there may be no symptoms other than the check engine light. It usually isn't an emergency, but get it diagnosed within a reasonable time, and sooner if the engine runs rough.

Is P0137 always a bad oxygen sensor?

No. A faulty sensor is a common cause, but both sources also list exhaust leaks, wiring faults and engine running problems. OBD-Codes.com adds misfires and very high or low fuel pressure, and RepairPal adds intake leaks, a bad coolant temperature sensor and PCM software.

What's the difference between P0137 and P0138?

Both are for the same sensor (Bank 1, Sensor 2, after the catalytic converter). P0137 means its voltage stayed too low, and P0138 means it stayed too high.

How much does it cost to fix P0137?

Neither source gives a repair cost. It can range from a wiring repair or exhaust leak fix to a new oxygen sensor or, less often, a catalytic converter, so get a diagnosis and a written estimate first.

Sources

  1. OBD-Codes.com: P0137 O2 Sensor Circuit Low Voltage (Bank 1, Sensor 2)
  2. RepairPal: P0137 O2 Sensor Circuit Low Voltage (rated Moderate)

Last reviewed 2026-10-22. Code definitions and repair steps can vary by manufacturer. Confirm with your vehicle's service information.