# P0135: O2 Sensor Heater Circuit (Bank 1 Sensor 1) **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:** $20-$400 - **Urgency:** Keep driving - **Most likely:** Upstream O2 sensor heater burned out - **DIY?:** Yes, moderate ## Quick answer P0135 means the heater inside the upstream oxygen sensor on bank 1 is not working correctly. The heater brings the sensor up to working temperature quickly after a cold start. A burned-out heater in the sensor is the most common cause, followed by a blown fuse. ## What does P0135 mean? An oxygen sensor only produces a useful signal once its ceramic tip is very hot, several hundred degrees. Exhaust heat alone would take minutes to get it there, so the upstream bank 1 sensor has a built-in electric heater. The engine computer powers it after a cold start so the sensor starts reporting quickly and the engine can switch to precise, closed-loop fuel control sooner. P0135 means the computer found the heater circuit not working as expected. Depending on the maker, it measures heater current, checks the control circuit voltage, or times how long the sensor takes to become active after a cold start. If the result is out of range, the code sets, often after two trips. Bank 1 is the side with cylinder 1, and sensor 1 is the sensor ahead of the catalytic converter. Some makers use P0030 for a closely related heater control fault on the same sensor. ## What are the symptoms of P0135? - Check engine light on - Car drives normally - Slightly worse fuel economy, mostly on short trips - Emissions monitor may show "not ready" ## What causes P0135? Ranked from most to least likely. Check them in this order: the cheap, common causes first. 1. **Burned-out heater in the upstream oxygen sensor** (most common). The heater element inside the sensor wears out from thousands of heat cycles and from vibration, much like an old light bulb. It is most common on sensors with high mileage. Unplugging the sensor and measuring resistance across the two heater pins shows an open circuit or a reading well outside the factory spec. 2. **Blown oxygen sensor heater fuse** (common). A single fuse often powers several sensor heaters and sometimes other engine parts. If more than one heater code is set, such as P0135 with P0141, check that fuse first. A fuse that blows again soon after replacement means something is shorted, often a heater or a wire rubbing on the exhaust. 3. **Damaged wiring or connector** (less common). Exhaust heat can melt wiring or the plug if a clip breaks or a heat shield is missing, and the harness can chafe on brackets as the engine moves. Look for burned, hardened or rubbed-through insulation and green corrosion in the connector. Damage often follows exhaust work where the harness was not re-secured. 4. **Engine computer heater control fault** (rare). The computer usually switches the heater's ground on and off. If its internal driver fails, the heater gets no power even though the sensor, fuse and wiring are fine. This is rare, so it is suspected only when every other part of the circuit tests good, and a shop should confirm it with a wiring diagram. ## How do you diagnose P0135? 1. Check the oxygen sensor heater fuse. 2. Unplug the bank 1 sensor 1 sensor and measure heater resistance between the two heater pins. 3. With the key on, confirm 12 volts on the heater feed wire at the harness connector. 4. Check that the computer is providing a ground signal to the heater using a test light or scan tool command. 5. Inspect the wiring along the exhaust for damage. ## How do you fix P0135, and what does it cost? | Fix | Typical cost | What it involves | | --- | --- | --- | | Replace the upstream oxygen sensor | $150-$400 | The heater cannot be repaired separately from the sensor. | | Replace the fuse or repair wiring | $20-$250 | Find and fix the cause of a blown fuse so it does not blow again. | Full price breakdowns: [oxygen sensor replacement cost](/cost/oxygen-sensor-replacement). ## Is it safe to drive with P0135? > **Safe to drive.** Yes, it is safe to drive. The engine just runs in a less precise mode for a few minutes after cold starts, which costs a little fuel. ## Will P0135 fail an emissions test? P0135 keeps the check engine light on, so the car fails an OBD-II emissions test in most states. A failed heater also stops the oxygen sensor heater monitor from completing, which leaves readiness showing "not ready". After the repair, clear the code and drive for several days, including cold starts, before going back for the test. ## After the repair: clearing P0135 Clear the code after replacing the sensor, fuse or wiring. Because the heater test usually runs after a cold start, let the car sit overnight, then start it and drive normally. On a scan tool, the sensor should become active quickly and the oxygen sensor heater monitor should read ready. No pending code after several cold starts confirms the fix. ## How to prevent P0135 - Find out why a heater fuse blew before replacing it, or it will blow again. - Keep oxygen sensor wiring clipped clear of the exhaust after any exhaust repair. - Buy a sensor that matches your engine's part number so the heater rating is correct. - Do not drop or strike a new sensor; the ceramic element inside can crack. - Keep cleaners and undercoating spray away from the oxygen sensor and its connector. ## Codes often seen with P0135 - [P0030](/codes/p0030): HO2S Heater Control Circuit (Bank 1 Sensor 1) - [P0141](/codes/p0141): O2 Sensor Heater Circuit (Bank 1 Sensor 2) - [P0131](/codes/p0131): O2 Sensor Circuit Low Voltage (Bank 1 Sensor 1) - [P0133](/codes/p0133): O2 Sensor Circuit Slow Response (Bank 1 Sensor 1) ## Frequently asked questions ### Can I drive with a P0135 code? Yes, P0135 is safe to drive with, and it will not hurt the engine. The sensor still warms from exhaust heat, just more slowly, so fuel economy drops slightly on short trips. You will likely fail an emissions test while the light is on, so fix it before your next inspection. ### Do I need to replace the whole oxygen sensor for P0135? Yes, if the heater has failed. The heater is built into the sensor and cannot be replaced on its own. Check the fuse first because it is cheaper, then measure the heater resistance. If it reads open or far out of spec, replacing the sensor is the only fix. ### What is the difference between P0135 and P0141? P0135 is the heater in the upstream sensor, before the catalytic converter, and P0141 is the heater in the downstream sensor after it. Both are on bank 1. The test is the same, but the sensor is different, so check which code you have before buying a part. ### How much does it cost to fix P0135? Most P0135 repairs cost $20-$400 at an independent shop. A blown fuse costs only a few dollars plus diagnosis, wiring repair runs up to about $250, and an upstream oxygen sensor installed is about $150-$400. The sensor's location and whether it is seized drive most of the labor cost. ### Can I fix P0135 myself? Often yes. With a multimeter you can check the fuse and measure the heater resistance yourself. If the heater has failed, an oxygen sensor socket and some penetrating oil usually get the old sensor out. Work only when the exhaust is cold. A shop helps when the sensor is seized or hard to reach. ### Can a blown fuse cause P0135? Yes. Many cars power the oxygen sensor heaters from one fuse, so a blown fuse can set P0135 along with other heater codes. Replacing the fuse may fix it, but a fuse rarely blows without a reason. Look for a shorted heater or a wire that has rubbed through near the exhaust. ### What should oxygen sensor heater resistance be? It depends on the sensor, so check service information for your engine. Many heaters read only a few ohms at room temperature, and an open reading, meaning no continuity, shows the heater has failed. Test across the two heater pins, which the wiring diagram identifies. ### Why does P0135 come back after a new sensor? A returning code usually means the real cause was missed. Common reasons are a replacement sensor with the wrong heater rating, a wiring fault that comes and goes, a corroded connector or a faulty heater control circuit. Use a sensor matched to your engine and inspect the harness along its full length. ### Does P0135 cause poor gas mileage? Slightly, mostly on short trips. Until the sensor warms up, the computer uses preset fuel values that are usually on the rich side. On longer drives, exhaust heat brings the sensor up to temperature and fuel control returns to normal. Drivers who mostly make short trips notice the difference most. ### Can cleaning the oxygen sensor fix P0135? No. P0135 is an electrical heater fault, not a dirty sensor. Cleaning the sensor tip will not repair a burned-out heater or a wiring problem. The fix is replacing the sensor, the fuse or the damaged wiring, depending on what the resistance and voltage tests show. ## Sources - [SAE J2012: Diagnostic Trouble Code Definitions](https://www.sae.org/standards/content/j2012_201812/) ## 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) - [P0136 O2 Sensor Circuit (Bank 1 Sensor 2)](https://diagxcar.com/codes/p0136) - [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) - [P0030 HO2S Heater Control Circuit (Bank 1 Sensor 1)](https://diagxcar.com/codes/p0030) - [P0141 O2 Sensor Heater Circuit (Bank 1 Sensor 2)](https://diagxcar.com/codes/p0141) - [P0155 O2 Sensor Heater Circuit (Bank 2 Sensor 1)](https://diagxcar.com/codes/p0155) - [P0161 O2 Sensor Heater Circuit (Bank 2 Sensor 2)](https://diagxcar.com/codes/p0161) ## Repair costs - [Oxygen sensor replacement cost](https://diagxcar.com/cost/oxygen-sensor-replacement): $150-$450 ## Warning lights linked to this - [Check engine light](https://diagxcar.com/warning-lights/check-engine) ## Terms explained - [What is Oxygen sensor?](https://diagxcar.com/glossary/oxygen-sensor) --- Source page: https://diagxcar.com/codes/p0135 Updated: 2026-11-03 General information, not a substitute for a qualified mechanic.