# P0155: O2 Sensor Heater Circuit (Bank 2 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-$500 - **Urgency:** Keep driving - **Most likely:** Burned-out heater in bank 2 upstream sensor - **DIY?:** Yes, moderate ## Quick answer P0155 means the engine computer found a problem with the electric heater inside the upstream oxygen sensor on bank 2. Without the heater, the sensor takes longer to start working after a cold start, so the engine runs on preset fueling for longer. A burned-out heater inside the sensor is the usual cause, followed by a blown fuse or damaged wiring. ## What does P0155 mean? An oxygen sensor only produces a useful signal once its tip is several hundred degrees hot. Exhaust heat alone takes minutes to get it there, so every modern sensor has a small electric heater built in. On most cars the heater gets 12 volts from a fuse or relay, and the engine computer switches the ground side on and off to control it. Bank 2 is the side of a V6, V8 or flat engine without cylinder 1, and sensor 1 is the upstream sensor ahead of the catalytic converter. The computer checks the heater by measuring the current it draws, watching the voltage on its control wire, or timing how long the sensor takes to become active after a cold start. If the reading falls outside the maker's limits, P0155 sets, often after two trips. Some makers, especially on engines with wide-band air-fuel ratio sensors, report the same fault as P0050, P0051 or P0052 instead. ## What are the symptoms of P0155? - Check engine light on, car drives normally once warm - Slightly rough running or poor mileage for the first few minutes after a cold start - Readiness monitors that will not complete for an emissions test - Other heater codes such as P0135 if a shared fuse has blown ## What causes P0155? Ranked from most to least likely. Check them in this order: the cheap, common causes first. 1. **Failed heater inside the bank 2 upstream sensor** (most common). The heater element is a thin resistor that cycles hot and cold on every drive, and it eventually cracks or burns open. This is most common on high-mileage sensors and on cars that see many short trips. A shop unplugs the sensor and measures heater resistance; an open circuit or a reading far from specification confirms it. 2. **Blown heater fuse or failed relay** (common). Many cars feed several oxygen sensor heaters from one fuse or relay. If that fuse blows, often because one heater shorted internally, every heater on it stops working. Seeing P0135, P0141 or P0161 alongside P0155 is the clue. Replace the fuse, then find out what blew it, or the new one will fail too. 3. **Heat-damaged or chafed wiring** (common). The bank 2 upstream sensor harness often runs close to the exhaust manifold, and on transverse V6s it can sit near the firewall where heat builds up. Melted insulation, a wire rubbed through on a bracket or a pigtail stretched after exhaust work can open or short the heater circuit. Look along the full harness, not just the plug. 4. **Corroded or loose connector** (less common). Water, road salt and heat cycles can corrode the connector pins or loosen their grip, adding resistance the computer reads as a heater fault. This is more common on older cars in snowy states. Green or white crust, a broken locking tab or a plug that wiggles freely are signs. Cleaning or replacing the connector fixes it. 5. **Engine computer heater driver fault** (rare). The computer switches the heater with an internal driver, and a shorted heater can occasionally damage it. Suspect this only when the sensor, fuse, power feed and wiring all test good and the control wire never switches. Some makers have technical bulletins or software updates for heater codes, so ask a dealer or shop to check. ## How do you diagnose P0155? 1. Read all codes; several heater codes at once point to a shared fuse or relay. 2. Check the oxygen sensor heater fuse and relay listed in the owner's manual. 3. Unplug the bank 2 upstream sensor and measure heater resistance at the sensor side of the plug. 4. With the key on, confirm 12 volts on the heater power wire at the harness side. 5. Inspect the harness along the exhaust for melting, chafing or pin corrosion before condemning the computer. ## How do you fix P0155, and what does it cost? | Fix | Typical cost | What it involves | | --- | --- | --- | | Replace bank 2 upstream oxygen sensor | $150-$450 | The heater is part of the sensor, so the whole sensor is replaced. | | Replace fuse or relay | $20-$120 | Cheap, but find the short that blew the fuse first. | | Repair heater wiring or connector | $100-$300 | More if the harness has to be rerouted away from the manifold. | Full price breakdowns: [oxygen sensor replacement cost](/cost/oxygen-sensor-replacement). ## Is it safe to drive with P0155? > **Safe to drive.** Yes, it is safe to drive. The sensor still works once exhaust heat warms it, so the main effects are slightly worse cold-start emissions and fuel use, plus a failed emissions test. ## Will P0155 fail an emissions test? P0155 lights the check engine lamp, which fails an OBD-based emissions test in most states. The oxygen sensor heater monitor cannot pass, and the oxygen sensor and catalyst monitors may also stay incomplete. Clearing the code resets every monitor, so allow several days of mixed driving after the repair before you go back for a retest. ## After the repair: clearing P0155 Clear the code, then let the car sit long enough to cool fully, ideally overnight. The heater test usually runs during the first minutes after a cold start, so drive normally from cold the next morning. The repair worked when the heater monitor reads complete, the sensor becomes active quickly on a scan tool, and no pending code returns. ## How to prevent P0155 - Keep the sensor harness clipped in its factory brackets after any engine or exhaust work. - Fix a blown heater fuse by finding the short, not by fitting a larger fuse. - Rinse road salt from under the engine bay in winter to slow connector corrosion. - Replace a sensor with the exact part number for its position, since heater ratings differ. - Avoid driving through deep water, which can crack a hot sensor and soak its plug. ## Codes often seen with P0155 - [P0135](/codes/p0135): O2 Sensor Heater Circuit (Bank 1 Sensor 1) - [P0161](/codes/p0161): O2 Sensor Heater Circuit (Bank 2 Sensor 2) - [P0141](/codes/p0141): O2 Sensor Heater Circuit (Bank 1 Sensor 2) - [P0030](/codes/p0030): HO2S Heater Control Circuit (Bank 1 Sensor 1) - [P0153](/codes/p0153): O2 Sensor Circuit Slow Response (Bank 2 Sensor 1) ## Frequently asked questions ### Can I drive with a P0155 code? Yes, P0155 is safe to drive with in the short term. The sensor still works once hot exhaust warms it, so the engine only loses precise fueling for the first few minutes after a cold start. The main downsides are slightly higher fuel use, more cold-start emissions and a failed inspection. ### What does bank 2 sensor 1 mean? Bank 2 sensor 1 is the upstream oxygen sensor, mounted before the converter, on the engine side opposite cylinder 1. Only V6, V8 and other two-bank engines have a bank 2. Your repair manual or a parts catalog shows which side that is, because it varies by maker and engine layout. ### How much does it cost to fix P0155? Most P0155 repairs cost $20 to $500 at an independent shop. A blown fuse or relay costs $20 to $120, while a new bank 2 upstream oxygen sensor runs about $150 to $450 installed. Wiring or connector repairs usually cost $100 to $300 depending on how much harness is damaged. ### Can I just replace the heater, not the sensor? No, the heater is sealed inside the oxygen sensor and cannot be replaced separately. If the heater tests open or out of range, the whole sensor has to be replaced. Avoid heater bypass tricks or resistors sold online; they do not restore proper warm-up and the code usually returns. ### Why do I have P0135 and P0155 at the same time? When two or more heater codes appear together, the most likely cause is a shared fuse, relay or power wire. Both upstream sensors rarely fail on the same day. Check the heater fuse first. If it is blown, a shorted heater or wire probably caused it, so find that before installing another fuse. ### Can I fix P0155 myself? Often yes, if you have a multimeter and an oxygen sensor socket. You can check the fuse, measure heater resistance at the sensor plug and replace an accessible sensor at home. Sensors on the rear bank of some transverse V6s are hard to reach and may be easier for a shop. ### Will P0155 hurt my catalytic converter? It is unlikely to cause damage on its own. The effect is limited to the first minutes after a cold start, when fueling is less precise. Still, a car that mostly makes short trips spends more of its time in that state, so fix the heater within a reasonable time rather than ignoring it. ### Will P0155 pass inspection? No, the check engine light alone fails an OBD-based emissions inspection in most states. The heater monitor also cannot complete while the fault is present. After the repair, drive for several days, including cold starts and some steady cruising, so the monitors read ready before you return for the test. ### Is P0155 the same on every car? The meaning is the same, but the exact test differs by maker. Some cars measure heater current, others watch the control wire or how quickly the sensor warms up. Engines with wide-band air-fuel sensors may use P0050, P0051 or P0052 for this fault instead, so check what your scan tool reports. ### What blows an oxygen sensor heater fuse? A heater that has shorted internally or a harness wire rubbing through to ground are the usual causes. The short draws more current than the fuse allows, so it blows. Unplug each sensor on that fuse and install a new fuse; if it holds, the unplugged sensor or its wiring is the problem. ## 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 - [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) - [P0141 O2 Sensor Heater Circuit (Bank 1 Sensor 2)](https://diagxcar.com/codes/p0141) - [P0151 O2 Sensor Circuit Low Voltage (Bank 2 Sensor 1)](https://diagxcar.com/codes/p0151) - [P0153 O2 Sensor Circuit Slow Response (Bank 2 Sensor 1)](https://diagxcar.com/codes/p0153) - [P0156 O2 Sensor Circuit (Bank 2 Sensor 2)](https://diagxcar.com/codes/p0156) - [P0157 O2 Sensor Circuit Low Voltage (Bank 2 Sensor 2)](https://diagxcar.com/codes/p0157) - [P0158 O2 Sensor Circuit High Voltage (Bank 2 Sensor 2)](https://diagxcar.com/codes/p0158) - [P0161 O2 Sensor Heater Circuit (Bank 2 Sensor 2)](https://diagxcar.com/codes/p0161) - [P0171 System Too Lean (Bank 1)](https://diagxcar.com/codes/p0171) ## Symptoms - [Why is my car getting bad gas mileage?](https://diagxcar.com/symptoms/poor-gas-mileage) ## Repair costs - [Oxygen sensor replacement cost](https://diagxcar.com/cost/oxygen-sensor-replacement): $150-$450 --- Source page: https://diagxcar.com/codes/p0155 Updated: 2026-11-03 General information, not a substitute for a qualified mechanic.