O2 Sensor Heater Circuit Bank 2 Sensor 1
The Powertrain Control Module (PCM) detected a malfunction in the heater circuit of the upstream oxygen sensor on Bank 2 (Sensor 1). This means the heater element is drawing too much or too little current, preventing the sensor from reaching its optimal operating temperature quickly.
While the vehicle is usually safe to drive, the engine may run rich or lean during warmup, leading to decreased fuel economy and potential long-term catalytic converter wear. It should be diagnosed and repaired soon.
Common symptoms
- Illuminated Check Engine Light (MIL)
- Decreased fuel efficiency
- Rough idle during cold starts
- Engine hesitation or stumbling before warming up
- Failure to pass an emissions test
Likely causes
- Faulty Bank 2 Sensor 1 oxygen sensor (failed internal heater element)
- Blown fuse for the oxygen sensor heater circuit
- Damaged, burned, or shorted wiring in the O2 sensor harness
- Corroded or loose electrical connector at the O2 sensor
- Poor ground connection for the heater circuit
- Faulty Powertrain Control Module (PCM) (rare)
What to check before replacing parts
Check the oxygen sensor heater fuse(s).
Look for: A blown fuse indicates a short in the heater circuit or the sensor itself, which must be addressed before replacing the sensor.
Visually inspect the Bank 2 Sensor 1 wiring harness and connector.
Look for: Look for melted wires from exhaust heat, chafing, or corrosion inside the connector pins that could interrupt the circuit.
Measure the resistance of the O2 sensor heater element using a multimeter.
Look for: Disconnect the sensor and probe the two heater pins; an open circuit (infinite resistance) or out-of-spec resistance confirms the internal heater has failed.
Verify battery voltage is reaching the O2 sensor heater connector.
Look for: With the key ON and engine OFF, probe the harness side of the connector; you should see approximately 12 volts on the power feed wire.
Check the ground circuit for the O2 sensor heater.
Look for: Measure continuity to ground on the harness side; high resistance or no continuity indicates a wiring issue between the sensor and the chassis or PCM.
This page explains the generic P0155 definition and is general reference information, not a diagnosis for your specific vehicle. Actual causes, severity, and repairs vary by make, model, engine, and mileage — always confirm with a scan tool and a qualified technician before replacing parts.
Gear guide: Best OBD2 ScannersRead this code yourself next time — from $20 Bluetooth dongles to bidirectional scan tools.Rather have a pro handle it? Find a vetted local mechanic.