P0155
UniversalO2 Sensor Heater Circuit Malfunction (Bank 2 Sensor 1)
The oxygen sensor at Bank 2 Sensor 1 has a heater that helps it reach operating temperature sooner. The vehicle’s control system monitors the heater circuit and has detected a malfunction. The code does not by itself prove the sensor needs replacement. The fault may delay accurate oxygen-sensor readings, increase emissions, or affect fuel economy; some vehicles may show no noticeable symptoms.
⚠️ Before You Begin (Safety First)
This code alone usually does not mean the vehicle must be stopped immediately. Stop driving if the engine runs very poorly, the warning light flashes, or you notice smoke, a strong fuel smell, or unusual overheating. Let the exhaust cool before inspecting nearby wiring, as exhaust components can cause burns.
Common Symptoms
- The check-engine light may be on because the control system detected a heater-circuit malfunction.
- There may be no noticeable change in how the vehicle runs.
- The sensor may take longer to reach operating temperature, delaying accurate oxygen readings after startup.
- Delayed or inaccurate readings may contribute to increased emissions or reduced fuel economy.
- If the underlying electrical fault affects other systems, drivability symptoms may occur, but they are not guaranteed by this code.
Common Causes
- An open, shorted, or otherwise faulty heater circuit in the Bank 2 Sensor 1 oxygen sensor.
- Damaged wiring, a poor electrical connection, corrosion, or heat-related damage near the sensor.
- A blown or faulty fuse supplying the heater circuit, where applicable.
- A problem with the circuit’s power supply or control electronics.
Diagnostic Steps
- Confirm the code with a scan tool and note any other stored codes; related codes can help point to a shared electrical or wiring issue.
- With the engine off and exhaust cool, visually inspect the Bank 2 Sensor 1 connector and reachable wiring for looseness, corrosion, chafing, or heat damage. Use the vehicle’s service information to identify the correct sensor.
- Check the owner’s manual or vehicle-specific service information for any relevant heater-circuit fuse, and inspect it only if the procedure is clear and safe.
- Avoid unplugging or testing circuits with improvised methods. If the wiring, connector, fuse, or sensor needs electrical testing, have a qualified technician follow the correct procedure for the vehicle.
- After any confirmed repair, clear the code only as directed and check whether it returns; a cleared code alone does not confirm the fault is fixed.
When to Call a Professional
Confirm the code and check related codes and available scan data before replacing parts. A technician can inspect the Bank 2 Sensor 1 connector and wiring, then test the heater circuit and its power and control using the vehicle-specific service information. Check relevant fuses and control circuits as applicable; consider the sensor, wiring, connections, or control electronics only after testing.
Compare component listings
Confirm diagnosis and vehicle fitment before buying. A listing does not prove that a part needs replacement. We may earn a commission from qualifying purchases.
Commonly Asked Questions
Does P0155 prove the oxygen sensor needs replacement?
No. It identifies a malfunction in the Bank 2 Sensor 1 heater circuit. The sensor, wiring, connector, fuse, power supply, or control electronics may be involved, so testing is needed before choosing a repair.
What does the oxygen sensor heater do?
It helps the sensor reach operating temperature sooner so it can provide useful oxygen readings earlier. The control system monitors the heater circuit for a malfunction.
Can I drive with P0155?
The code alone often does not require an immediate stop, but it may affect emissions or fuel economy. Stop if the engine runs very poorly, the warning light flashes, or you notice smoke, a strong fuel smell, or overheating.
How can I distinguish a sensor problem from a wiring problem?
A visual inspection may reveal damage or a poor connection, but electrical tests using vehicle-specific service information are usually needed to distinguish a sensor heater fault from a wiring, fuse, supply, or control problem.
Browse Available Code Guides
Previous and next available guides in database record order, across makes. Adjacent entries may share a code number and do not necessarily describe related faults.