# P0137: O2 Sensor Circuit Low Voltage (Bank 1 Sensor 2) **Verdict:** Safe to drive Oxygen sensors - Generic OBD-II code, applies to all gasoline cars and light trucks sold in the US since 1996. - **Typical cost:** $100-$400 - **Urgency:** Keep driving - **Most likely:** Exhaust leak or failed downstream O2 sensor - **DIY?:** Steps 1-3 ## Quick answer P0137 means the downstream oxygen sensor on bank 1, after the catalytic converter, is reading a voltage that stays too low. A low reading means the sensor thinks the exhaust is lean. An exhaust leak near the sensor or a failed sensor is the most common cause. ## What does P0137 mean? The downstream oxygen sensor on bank 1 sits after the catalytic converter. Because a working converter stores oxygen and evens out the exhaust, this sensor normally reads fairly steady and on the high side, often around 0.5 to 0.8 volt at cruise on a narrow-band sensor. The computer uses it to judge the converter and, on many cars, to make small, slow fuel corrections. P0137 sets when the downstream signal stays below a low threshold, often well under about 0.2 volt depending on the maker, under conditions where it should read higher. Some makers run an active test, briefly richening the mixture or waiting for a period of rich running, and set the code if sensor 2 never rises. A steady low reading usually means outside air is reaching the sensor, the signal is shorted to ground, or the sensor has failed. Bank 1 is the side with cylinder 1, and sensor 2 is after the converter. ## What are the symptoms of P0137? - Check engine light on - Car usually runs normally - Ticking or puffing sound from under the car if there is an exhaust leak - Catalyst monitor not ready, or a failed emissions test ## What causes P0137? Ranked from most to least likely. Check them in this order: the cheap, common causes first. 1. **Exhaust leak ahead of or near the downstream sensor** (most common). A rusted pipe, cracked flex joint, leaking converter flange or loose clamp lets outside air into the exhaust near sensor 2. The sensor reads that extra oxygen as lean and its voltage stays low. Leaks like this are very common on older cars in road-salt states and are often louder on a cold start. 2. **Failed downstream oxygen sensor** (common). An aged or contaminated sensor can lose output and sit near zero volts. It is more likely after many years and miles or on engines that burn oil or leak coolant. If the exhaust is sealed and the wiring is good, but the signal stays low even with the engine briefly running rich, the sensor is likely dead. 3. **Signal wire shorted to ground** (less common). The downstream harness runs under the car, where it can rub against the body, heat shields or exhaust hangers. If the signal wire wears through and touches metal, the reading is dragged toward zero. Previous exhaust or transmission work near the harness raises the odds. Inspect the wire run closely for shiny or melted spots. 4. **Engine running lean overall** (less common). If the whole engine is lean from a vacuum leak, a dirty MAF sensor or low fuel pressure, the downstream sensor may simply be reporting it. Lean codes such as P0171 and high positive fuel trims are the clue. In that case the upstream sensor usually reads lean too, and fixing the lean condition clears both. 5. **Engine computer fault** (rare). The engine computer reads the downstream signal and supplies its reference or bias. An internal fault can drag a good signal down or misread it. This is uncommon and is usually confirmed only after the sensor, wiring and exhaust have been ruled out. Software updates are sometimes available, so a shop may check service bulletins. ## How do you diagnose P0137? 1. Read all codes; P0171 or other lean codes mean the engine itself may be lean, not just the sensor. 2. Warm the engine and graph bank 1 sensor 2; at steady cruise it normally sits fairly high and steady, not near zero. 3. Briefly add fuel, for example with a quick throttle snap; a working downstream sensor should rise above about 0.6 volt. 4. Look and listen for exhaust leaks around the converter, flex pipe and sensor, ideally on a cold start. 5. Inspect the wiring under the car for a short to ground, then replace the sensor if the exhaust and circuit are good. ## How do you fix P0137, and what does it cost? | Fix | Typical cost | What it involves | | --- | --- | --- | | Repair an exhaust leak near the sensor | $100-$400 | Gaskets and clamps cost less; replacing a rusted pipe or flex section costs more. | | Replace the downstream oxygen sensor | $150-$400 | The fix when the sensor stays low with a sealed exhaust and good wiring. | | Repair wiring shorted to ground | $100-$250 | Repairs and re-routes the harness away from the body or heat shields. | Full price breakdowns: [oxygen sensor replacement cost](/cost/oxygen-sensor-replacement), [muffler replacement cost](/cost/muffler-replacement). ## Is it safe to drive with P0137? > **Safe to drive.** Yes, it is generally safe to drive. Have exhaust leaks checked soon, though, because a leak under the car can let exhaust fumes into the cabin, and stop driving if you smell exhaust inside the car. ## Will P0137 fail an emissions test? P0137 keeps the check engine light on, which fails an OBD-II emissions test in most states. A downstream sensor reading low also stops the catalyst monitor from giving a valid result, so it usually shows not ready. After the repair and clearing the code, drive several days, including steady highway cruising, until the oxygen sensor and catalyst monitors finish. ## After the repair: clearing P0137 After the repair, clear the code and drive. At steady cruise on a warm engine, bank 1 sensor 2 should hold a fairly steady, higher reading instead of sitting near zero. After several trips, the oxygen sensor and catalyst monitors should read complete with no pending code, which means the fix worked. ## How to prevent P0137 - Have rusted exhaust pipes, flanges and flex joints near the converter checked during routine service. - Fix exhaust leaks promptly, since outside air is the leading cause of a low downstream reading. - Keep the downstream harness clipped up and away from heat shields and the body. - Address lean codes such as P0171 early so the whole engine does not run lean. ## Codes often seen with P0137 - [P0136](/codes/p0136): O2 Sensor Circuit (Bank 1 Sensor 2) - [P0138](/codes/p0138): O2 Sensor Circuit High Voltage (Bank 1 Sensor 2) - [P0139](/codes/p0139): O2 Sensor Circuit Slow Response (Bank 1 Sensor 2) - [P0140](/codes/p0140): O2 Sensor Circuit No Activity Detected (Bank 1 Sensor 2) - [P0420](/codes/p0420): Catalyst System Efficiency Below Threshold (Bank 1) - [P0171](/codes/p0171): System Too Lean (Bank 1) ## Frequently asked questions ### Can I drive with a P0137 code? Yes, P0137 is generally safe to drive with because the downstream sensor has little effect on how the engine runs. The main issues are a failed emissions test and a converter test that cannot finish. If an exhaust leak is involved, fix it soon and watch for exhaust smell inside the car. ### What is the most common cause of P0137? An exhaust leak near the downstream sensor is a very common cause of P0137, along with a failed sensor. Outside air entering the exhaust makes the sensor read lean and low. Shorted wiring and a truly lean engine are less common, and computer faults are rare. ### How much does it cost to fix P0137? Most P0137 repairs cost $100 to $400 at an independent shop. Exhaust leak repairs run about $100 to $400 depending on the part, and a downstream oxygen sensor about $150 to $400. Wiring repairs usually cost $100 to $250, including diagnosis of where the wire is shorted. ### What is the difference between P0131 and P0137? Both mean low oxygen sensor voltage on bank 1, but on different sensors. P0131 is the upstream sensor ahead of the converter, which controls fuel. P0137 is the downstream sensor after the converter, which mainly checks the converter. P0137 rarely affects how the car runs. ### Can a bad catalytic converter cause P0137? Not usually. A worn converter stores less oxygen, which tends to make the downstream sensor switch like the upstream one and sets P0420, not a steady low voltage. A steady low reading more often comes from an exhaust leak, a failed sensor or wiring shorted to ground. ### Can I fix P0137 myself? You can check for exhaust leaks, inspect the wiring and replace the downstream sensor yourself on many cars. The sensor is usually under the car behind the converter and comes out with an oxygen sensor socket. Welding or replacing rusted pipe is usually a shop job. ### How do I find an exhaust leak? Listen under the car on a cold start for ticking or puffing, and look for black soot marks at joints, flanges and the flex pipe. A shop can use a smoke machine for small leaks. Never hold your hand near the exhaust when it is hot, and keep fingers away from moving parts. ### Will P0137 affect gas mileage? Usually very little. On most cars the downstream sensor only makes small, slow fuel corrections, so the effect on mileage is minor. If mileage dropped a lot, look for a lean condition or another code. A large exhaust leak can also cause noise and fumes, which deserve attention. ### Should I replace the upstream sensor too? Not unless it has its own code or tests bad. P0137 points to the downstream sensor or its surroundings. If both sensors are original on a high-mileage car, replacing the upstream one as well is reasonable but not required to fix P0137. ### Why did P0137 come back after a new sensor? The cause was probably not the sensor. An exhaust leak near the sensor or a signal wire shorted to ground will keep the reading low with any sensor. Recheck the exhaust for leaks and the harness for damage, and make sure the new part is correct for bank 1 sensor 2. ## Sources - [SAE J2012: Diagnostic Trouble Code Definitions](https://www.sae.org/standards/content/j2012_201812/) - [EPA: On-Board Diagnostics (OBD)](https://www.epa.gov/state-and-local-transportation/vehicle-emissions-board-diagnostics-obd) ## Other oxygen sensors codes - [P0130 O2 Sensor Circuit (Bank 1 Sensor 1)](https://diagxcar.com/codes/p0130) - [P0131 O2 Sensor Circuit Low Voltage (Bank 1 Sensor 1)](https://diagxcar.com/codes/p0131) - [P0132 O2 Sensor Circuit High Voltage (Bank 1 Sensor 1)](https://diagxcar.com/codes/p0132) - [P0133 O2 Sensor Circuit Slow Response (Bank 1 Sensor 1)](https://diagxcar.com/codes/p0133) - [P0134 O2 Sensor Circuit No Activity Detected (Bank 1 Sensor 1)](https://diagxcar.com/codes/p0134) - [P0135 O2 Sensor Heater Circuit (Bank 1 Sensor 1)](https://diagxcar.com/codes/p0135) - [P0136 O2 Sensor Circuit (Bank 1 Sensor 2)](https://diagxcar.com/codes/p0136) - [P0138 O2 Sensor Circuit High Voltage (Bank 1 Sensor 2)](https://diagxcar.com/codes/p0138) - [P0139 O2 Sensor Circuit Slow Response (Bank 1 Sensor 2)](https://diagxcar.com/codes/p0139) - [P0140 O2 Sensor Circuit No Activity Detected (Bank 1 Sensor 2)](https://diagxcar.com/codes/p0140) ## Repair costs - [Oxygen sensor replacement cost](https://diagxcar.com/cost/oxygen-sensor-replacement): $150-$450 - [Muffler replacement cost](https://diagxcar.com/cost/muffler-replacement): $200-$600 --- Source page: https://diagxcar.com/codes/p0137 Updated: 2026-11-03 General information, not a substitute for a qualified mechanic.