P0137 typically means the downstream (Bank 1) oxygen sensor is reporting a voltage that’s too low. In practice, this usually points to a faulty sensor or wiring issue rather than a catastrophic engine fault.
This article explains what P0137 means, the most common causes, how to diagnose it, and practical steps to repair it. The guidance is general and applicable to most vehicles with OBD-II systems, but always consult your vehicle’s service manual for model-specific wiring diagrams and specifications.
What P0137 Means
P0137 is a diagnostic trouble code indicating Bank 1 Sensor 2 (the oxygen sensor located downstream, after the catalytic converter) is reporting a low voltage reading. Because this sensor monitors the efficiency of the catalytic converter rather than the air-fuel mixture in real time, a consistently low signal can trigger the code even if the engine itself seems to run smoothly.
Common Causes
Several issues can lead to P0137. Inspect these possibilities in order of likelihood and cost.
- Faulty Bank 1 Sensor 2 (downstream O2 sensor)
- Damaged, corroded, or disconnected wiring or connector to the sensor
- Exhaust leaks around the sensor or before it that distort sensor readings
- Intermittent PCM/ECM fault or incorrect sensor calibration
Keeping an eye on related codes (like P0138, P0140, or P0171) and monitoring live data can help differentiate between a sensor problem and an electrical/wiring issue.
How to Diagnose
The following steps outline a practical approach to identify the root cause of P0137. Proceed with caution and consult a professional if you’re unsure at any point.
- Check for other stored codes and review freeze frame data to confirm the issue is persistent rather than temporary.
- Inspect the Bank 1 Sensor 2 wiring harness and connector for visible damage, corrosion, or loose pins.
- Look for exhaust leaks around the sensor that could affect readings. Repair any leaks before retesting.
- Use live data if available: verify that the downstream sensor’s voltage is consistently low and does not fluctuate with engine operating conditions.
- Test the sensor with a multimeter (if you have the lab skills): measure the sensor’s heater circuit and signal circuit resistance per the manufacturer’s spec; compare against spec values.
- If wiring and sensor appear OK, consider swapping the sensor with a known-good downstream sensor (if feasible) to see if the code clears or moves to the other bank.
After completing diagnostics, perform a road test to confirm the issue is resolved and use the scanner to clear the codes. If the code returns, re-check wiring and, if necessary, replace the sensor or consider a PCM issue as a last resort.
Repair and Fixes
Based on your diagnostic results, apply the appropriate repair in the following order to minimize cost and downtime.
- Replace the Bank 1 Sensor 2 if the sensor is faulty, contaminated, or fails resistance/response tests.
- Repair or replace damaged wiring or connectors to Bank 1 Sensor 2; ensure a clean, secure connection and proper ground.
- Repair exhaust leaks around the sensor or in the exhaust system portion that could influence readings.
- After repairs, clear the codes with your scan tool and run a road test to verify the issue is resolved and the sensor voltage behaves normally.
- If the code reappears, recheck all wiring, consider sensor calibration or PCM issues, and consult a professional with access to vehicle-specific diagnostic flowcharts.
Notes: If your vehicle has a warranty or extended service plan, check coverage for oxygen sensors and related wiring. Oxygen sensors are a common wear item and may be covered under certain maintenance plans.
Summary
P0137 points to a low voltage reading from Bank 1 Sensor 2, the downstream oxygen sensor. Start with a mechanical and electrical inspection of the sensor and its harness, look for exhaust leaks, and test the sensor’s functionality. Replace the sensor if it’s faulty, repair any wiring issues, and verify the fix with a road test and a code clear. If the problem persists, broaden diagnostics to include the PCM and related emissions components.
Regular maintenance and timely replacement of aged oxygen sensors can prevent P0137 and help keep emissions in check. Always refer to your vehicle’s service manual for model-specific guidance and torque specs.