P0155 OBD2 Code Guide
P0155 is a powertrain diagnostic trouble code. Use this hub to understand the plain meaning, the first checks to run, and which vehicle-specific guides may be more useful before replacing parts.
O2 Sensor Heater Circuit Malfunction (Bank 2, Sensor 1)
Code P0155 indicates a problem with the heater circuit of the upstream oxygen sensor on Bank 2. This sensor, often referred to as Sensor 1, is located before the catalytic converter on the engine bank that does not contain cylinder #1. The heater circuit is crucial because it rapidly brings the oxygen sensor to its optimal operating temperature (typically around 600°F or 315°C). Without proper heating, the sensor takes longer to become active and provide accurate air-fuel ratio data to the Powertrain Control Module (PCM). This delay can lead to the PCM making incorrect fuel trim adjustments, resulting in increased emissions, reduced fuel economy, and potentially other drivability issues. The PCM sets P0155 when it detects an electrical fault within this heater circuit, such as an open circuit, a short circuit, or resistance outside the specified range.
Code verification standard
P0155 is published with SAE J2012 / ISO 15031-6 code structure plus OBD2 P0155 diagnostic context.
First checks
- - Read all stored and pending codes before clearing anything.
- - Save freeze-frame data so you know speed, load and temperature when the code set.
- - Inspect wiring, connectors, fuses, hoses and obvious leaks tied to the named system.
- - Compare live data against realistic values before buying sensors or modules.
- - Clear the code only after repair and complete a drive cycle to confirm it does not return.
P0155 diagnostic path
- 11. **Visual Inspection of Wiring and Connector:** Locate the Bank 2, Sensor 1 oxygen sensor. Carefully inspect its electrical connector and the wiring harness leading to it. Look for any signs of damage such as frayed wires, melted insulation, corrosion on the terminals, or loose connections. Ensure the sensor itself is securely mounted and free from physical damage.
- 22. **Check Heater Circuit Resistance:** Disconnect the O2 sensor's electrical connector. Using a multimeter, measure the resistance across the two heater wires within the sensor's pigtail (these are typically the same color, often white or black). Compare this reading to the manufacturer's specifications (usually between 2-10 ohms). An open circuit (infinite resistance) or a reading significantly outside the specified range indicates a faulty heater element within the sensor.
- 33. **Verify Power Supply to Heater Circuit:** With the ignition ON (engine OFF), use a multimeter to check for 12-volt power at one of the heater circuit terminals in the vehicle's wiring harness connector (the side that connects to the sensor). This power typically comes from a fuse or relay. If no power is present, trace the circuit back to the fuse box and check for a blown fuse or a faulty relay.
- 44. **Inspect Ground Circuit Integrity:** With the ignition OFF, check for a good ground connection at the other heater circuit terminal in the vehicle's wiring harness connector. This can be done by checking for continuity to a known good chassis ground using a multimeter. A high resistance or open circuit indicates a problem with the ground wire or its connection.
- 55. **Monitor O2 Sensor Data with Scan Tool (Post-Repair Verification):** After addressing any identified issues, clear the code and test drive the vehicle. Use a scan tool to monitor the Bank 2, Sensor 1 O2 sensor's voltage readings and heater circuit status. Ensure the sensor quickly reaches operating temperature and provides consistent, fluctuating voltage readings, indicating proper operation.
Verify before repair
- - Replace the Bank 2, Sensor 1 Oxygen Sensor: This is the most common solution, as the heater element within the sensor frequently fails over time.
- - Repair or Replace Damaged Wiring/Connector: If the visual inspection revealed frayed wires, melted insulation, or corroded terminals, repair or replace the affected section of the wiring harness or the connector.
- - Check and Replace Blown Fuse or Faulty Relay: If no power was detected at the heater circuit, identify and replace any blown fuses or faulty relays that supply power to the O2 sensor heater circuit.
Vehicle-specific pages to check next
Searches this page covers
These queries are answered in this guide without creating thin duplicate pages.