Quick answer: The P0137 code indicates that the downstream oxygen sensor on Bank 1 (Sensor 2) is sending a sustained low-voltage signal to the engine computer, usually below 0.2 volts. It affects the emissions control system. While safe for short trips, it requires inspection to rule out exhaust leaks or wiring faults.
Seeing code P0137 on your diagnostic tool means your vehicle’s engine control module has detected an abnormally low voltage reading from the rear oxygen sensor. Below, you will find a clear explanation of what triggered this code, the symptoms you might experience, and step-by-step diagnostic steps to fix the problem without wasting money on unneeded parts.
What Does P0137 Mean?
Your engine uses oxygen sensors to evaluate combustion efficiency and monitor exhaust gases. Bank 1 Sensor 2 is located downstream, mounted directly behind the catalytic converter on the side of the engine housing cylinder 1. The computer expects this sensor to maintain a stable reading between 0.45 and 0.55 volts once warm. When the sensor reports a voltage below roughly 0.15 to 0.2 volts for an extended duration, the computer interprets the mixture as excessively lean or suspects a broken circuit, setting code P0137.
Symptoms
- Check engine light on the dashboard
- Failed emissions or smog inspection
- Hissing, puffing, or ticking noises under the floorboard from an exhaust leak
- Slight decrease in fuel efficiency
- Faint smell of unburned exhaust gases
Possible Causes
A common mistake is replacing the catalytic converter immediately when a downstream code appears, even though electrical and exhaust issues are far more frequent culprits.
- Exhaust leak near or just upstream of the sensor bung, drawing outside air into the pipe
- Damaged, melted, or corroded oxygen sensor wiring harness or connector
- Defective downstream oxygen sensor (Bank 1, Sensor 2)
- Severe engine lean condition caused by vacuum leaks or low fuel pressure
- Degraded catalytic converter unable to store oxygen properly
Check These Yourself Before Visiting a Mechanic
- Look under the vehicle along the exhaust pipe to check if the sensor wiring is frayed, detached, or melted against hot metal.
- Start the engine cold and listen near the catalytic converter for ticking or hissing sounds that indicate an exhaust leak.
- Inspect the electrical plug on the sensor to ensure it is clipped tightly and free of road debris, oil, or moisture.
How to Fix It
- Connect a scan tool with live data capability to observe Bank 1 Sensor 2 voltage; verify if it remains completely flatlined near zero.
- Inspect the exhaust pipes, flanges, and welds ahead of Sensor 2 for cracks or loose hardware, repairing any leaks first.
- Test the sensor harness with a digital multimeter for reference voltage, ground integrity, and continuity back to the computer.
- Replace the Bank 1 Sensor 2 oxygen sensor if the wiring tests good but the signal fails to fluctuate normally.
- Check fuel trims and air intake piping if new sensor data shows a genuine engine-wide lean condition.
Estimated Repair Costs (2026)
| Job | Parts ($) | Labor ($) |
|---|---|---|
| Exhaust Leak Repair / Gasket | $20 – $90 | $90 – $220 |
| Wiring or Connector Repair | $15 – $60 | $80 – $160 |
| Downstream O2 Sensor Replacement | $60 – $190 | $70 – $140 |
| Catalytic Converter Replacement | $450 – $1,900 | $160 – $450 |
Note: these are 2026 estimates in US dollars; costs vary by make and model.
Frequently Asked Questions
Can I drive with the P0137 code?
Yes, driving short distances is generally safe because Sensor 2 mainly tracks catalytic converter efficiency rather than primary fuel delivery. However, you should inspect it promptly to prevent false emissions readings or masking underlying exhaust leaks.
How do I clear the P0137 code?
Once you repair the physical fault, you can clear the code using an OBD-II scanner. Alternatively, the computer will automatically clear the code after you complete several drive cycles without the low-voltage condition returning.
Which sensor is Bank 1 Sensor 2 on a V6 or V8 engine?
Bank 1 is always the side of the engine block that houses cylinder number 1. Sensor 2 is the downstream sensor installed directly after the catalytic converter on that same exhaust bank.