# P0136: O2 Sensor Circuit (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:** Failed downstream O2 sensor or wiring - **DIY?:** Steps 1-3 ## Quick answer P0136 means the engine computer has found a general problem with the signal from the downstream oxygen sensor on bank 1, the one after the catalytic converter. The reading is out of range or not behaving as expected. A failed sensor or damaged wiring under the car is the usual cause. ## What does P0136 mean? The downstream oxygen sensor on bank 1 sits in the exhaust after the catalytic converter. Its main job is to check the converter: a healthy converter stores oxygen, so this sensor's signal stays fairly steady while the upstream sensor switches rapidly. On many cars the computer also uses it for a slow, small correction to fuel control. On most four-cylinder engines it is the only sensor behind the converter. P0136 is a general circuit code, and makers define it differently. Some set it when the signal sits outside its normal range, some when it is stuck at a fixed value as if the circuit were open, and some when the sensor does not react during a test where the computer briefly changes the mixture. More specific codes cover low voltage (P0137), high voltage (P0138), slow response (P0139) and no activity (P0140). Bank 1 is the side with cylinder 1, and sensor 2 is the second sensor, after the converter. ## What are the symptoms of P0136? - Check engine light on - Car usually drives exactly as before - Catalyst monitor not ready or a failed emissions test - Catalytic converter code such as P0420 may appear with it ## What causes P0136? Ranked from most to least likely. Check them in this order: the cheap, common causes first. 1. **Failed downstream oxygen sensor** (most common). The downstream sensor runs cooler than the upstream one, but it still ages and can drift, go erratic or fail open after many years and miles. Oil burning and coolant leaks shorten its life. If the wiring and exhaust check out but the signal is implausible on a warm engine, the sensor is the usual culprit. 2. **Damaged wiring or connector under the car** (common). The downstream sensor harness runs along the underside of the car, where road debris, rust, heat shields and jacking points can damage it. Connectors there collect water and salt, especially in snow-belt states. A broken, chafed or corroded wire can make the signal drop out or read wrong, so inspect the whole run. 3. **Exhaust leak near the downstream sensor** (common). A rusted pipe, cracked flex joint or leaking flange near the sensor lets outside air reach it, so it reports oxygen that is not really there. This is common on older cars in road-salt areas. A leak can also make a good converter look bad, which is why P0420 sometimes appears with P0136. 4. **Wrong or poor-quality replacement sensor** (less common). Downstream sensors may look like upstream ones but can differ in connector, wire length or heater rating. A wrong or very low-quality part may send a signal the computer does not accept. This usually shows up soon after a recent sensor replacement, so compare the part number with the correct one for your engine. 5. **Engine computer fault** (rare). The computer supplies a bias voltage and reads the downstream signal, so an internal fault can make a good sensor appear faulty. This is uncommon and should be considered only after the sensor, wiring and exhaust have been checked. Some makers offer software updates for false oxygen sensor codes, so a shop may check service bulletins. ## How do you diagnose P0136? 1. Read all codes; catalyst or upstream sensor codes help show whether the problem is the sensor, the exhaust or the converter. 2. Warm the engine and graph bank 1 sensor 2 with sensor 1; the downstream signal should be steadier and usually sit fairly high, often around 0.5 to 0.8 volt at cruise. 3. Inspect the downstream wiring and connector along the underside of the car for damage, rust and water. 4. Check for exhaust leaks near the sensor and at the converter flanges. 5. Test the circuit with a wiring diagram before replacing the sensor, especially if it is fairly new. ## How do you fix P0136, and what does it cost? | Fix | Typical cost | What it involves | | --- | --- | --- | | Replace the downstream oxygen sensor | $150-$400 | Usually easier to reach than the upstream sensor on most cars. | | Repair wiring or connector | $100-$250 | Fixes damaged, chafed or corroded wiring under the car. | | Repair an exhaust leak near the sensor | $100-$400 | Gaskets and clamps cost less; a rusted pipe section costs more. | Full price breakdowns: [oxygen sensor replacement cost](/cost/oxygen-sensor-replacement). ## Is it safe to drive with P0136? > **Safe to drive.** Yes, it is generally safe to drive. The downstream sensor has only a small role in fuel control on most cars, so the main downside is a failed emissions test and possibly a false converter code. ## Will P0136 fail an emissions test? P0136 keeps the check engine light on, which fails an OBD-II emissions test in most states. Because the downstream sensor is how the computer checks the converter, the catalyst monitor usually cannot complete either. After the repair and clearing the code, drive several days, including some steady highway cruising, until both the oxygen sensor and catalyst monitors read ready. ## After the repair: clearing P0136 Clear the code after the repair. On a warm engine at steady cruise, bank 1 sensor 2 should read fairly steady while sensor 1 switches. Drive several trips, including some steady highway speed, then confirm that the oxygen sensor and catalyst monitors are complete and that no pending code has returned. ## How to prevent P0136 - Have exhaust leaks and rusted pipes near the converter fixed before they affect the sensor. - Check that the downstream connector is clipped up and away from road spray. - Repair oil burning or coolant leaks, which shorten oxygen sensor life. - Use a direct-fit sensor with the correct connector instead of splicing a universal one. ## Codes often seen with P0136 - [P0137](/codes/p0137): O2 Sensor Circuit Low Voltage (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) - [P0141](/codes/p0141): O2 Sensor Heater Circuit (Bank 1 Sensor 2) - [P0420](/codes/p0420): Catalyst System Efficiency Below Threshold (Bank 1) ## Frequently asked questions ### Can I drive with a P0136 code? Yes, P0136 is generally safe to drive with. The downstream sensor mainly checks the catalytic converter, so the car usually runs normally. You will fail an emissions test while the light is on, and the catalyst monitor cannot finish, so plan a repair within a few weeks. ### Where is bank 1 sensor 2? Bank 1 sensor 2 is the oxygen sensor after the catalytic converter on the side of the engine with cylinder 1. It usually threads into the exhaust pipe under the car, just behind the converter. On a four-cylinder engine it is typically the only sensor behind the converter. ### How much does it cost to fix P0136? Most P0136 repairs cost $100 to $400 at an independent shop. Replacing the downstream sensor runs about $150 to $400, depending on the part and how rusted it is. Wiring repairs cost about $100 to $250, and an exhaust leak near the sensor about $100 to $400. ### Does P0136 mean my catalytic converter is bad? No, P0136 points to the downstream sensor circuit, not the converter itself. A faulty downstream sensor can, however, make the converter test fail and set P0420. Fix the sensor or wiring first, then drive several trips to see whether a converter code really returns before buying a converter. ### What is the difference between P0136 and P0141? Both involve the same downstream sensor, but different circuits. P0136 is about the sensor signal, meaning the reading is out of range or not behaving correctly. P0141 is about the built-in heater that warms the sensor. A bad sensor can set both, but wiring faults can set only one. ### Can I replace the downstream oxygen sensor myself? Often, yes. The downstream sensor is usually reachable from under the car with an oxygen sensor socket, though rust can make it tight. Lift and support the car safely on stands, and let the exhaust cool. Use penetrating oil and new anti-seize if the sensor did not come with it. ### Does P0136 affect gas mileage? Usually only a little, if at all. On most cars the upstream sensor does the main fuel control, while the downstream sensor makes small, slow corrections. Some cars may run a bit off if the computer uses a bad downstream reading, but a large drop in mileage points to another problem. ### Can an exhaust leak cause P0136? Yes. A leak near the downstream sensor can let outside air reach it, which skews its reading and can make the circuit look faulty. Rusted pipes, cracked flex joints and leaking flanges are common on older cars. Fixing the leak first can save you from replacing a working sensor. ### Can I just unplug the downstream oxygen sensor? No. Unplugging it sets more codes, keeps the check engine light on and stops the converter test, so the car will fail an emissions test. Tampering with emissions controls is also illegal under federal law. The sensor is usually one of the cheaper and easier parts to replace. ### Is the downstream sensor the same as the upstream one? Not always. On many cars the two look alike but use different connectors, wire lengths or, on newer engines, different sensor types. The upstream sensor may be an air-fuel ratio sensor while the downstream one is narrow-band. Buy the part listed for your exact position: 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) - [P0137 O2 Sensor Circuit Low Voltage (Bank 1 Sensor 2)](https://diagxcar.com/codes/p0137) - [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 --- Source page: https://diagxcar.com/codes/p0136 Updated: 2026-11-03 General information, not a substitute for a qualified mechanic.