P0155
UniversalOxygen Sensor Heater Circuit Malfunction (Bank 2 Sensor 1)
Medium SeverityThis code indicates an electrical problem with the heating element inside the oxygen sensor on Bank 2 Sensor 1. This failure prevents the sensor from reaching its optimal operating temperature quickly, leading to increased emissions and potentially reduced fuel efficiency until the engine warms up.
⚠️ Before You Begin (Safety First)
Always ensure the vehicle is safely supported on jack stands before working underneath. Allow the exhaust system to cool completely to prevent burns. Disconnect the battery before performing any electrical work.
Common Symptoms
- Check Engine Light illuminated
- Decreased fuel economy
- Increased exhaust emissions
- Engine may run rich or lean
- Failed emissions test
Common Causes
- Faulty oxygen sensor heater element (most common)
- Open or short in the oxygen sensor heater circuit wiring
- Blown fuse for the O2 sensor heater circuit
- Corroded or loose electrical connectors
- Faulty Powertrain Control Module (PCM) (rare)
Frequently reported on: General/Universal
Diagnostic Steps
- Safely lift and support the vehicle.
- Locate Bank 2 Sensor 1. This is the oxygen sensor before the catalytic converter on the bank of cylinders that does not contain cylinder #1.
- Disconnect the electrical connector for the oxygen sensor.
- Use an oxygen sensor wrench or a standard wrench to remove the old sensor.
- Apply anti-seize compound to the threads of the new oxygen sensor.
- Install the new oxygen sensor, ensuring it is tightened to specification.
- Reconnect the electrical connector.
- Lower the vehicle.
- Clear the P0155 code using an OBD-II scanner.
- Test drive the vehicle to confirm the repair.
👨🔧 When to Call a Professional
If after replacing the oxygen sensor, the code persists, or if you are unsure about diagnosing electrical circuits, it is best to consult a professional mechanic. This could indicate a wiring issue or a problem with the Powertrain Control Module (PCM).
Commonly Asked Questions
What does "Bank 2 Sensor 1" mean?
"Bank 2" refers to the side of the engine that does NOT contain cylinder #1. "Sensor 1" refers to the upstream oxygen sensor, located before the catalytic converter.
Can I drive with a P0155 code?
While you can usually drive with this code, it's not recommended for long. It will lead to increased emissions, reduced fuel economy, and may prevent your vehicle from passing an emissions test.
Is replacing an oxygen sensor difficult?
It's generally a medium difficulty DIY repair. The main challenges can be accessing the sensor and dealing with a sensor that is seized due to heat and corrosion.
Do I need special tools to replace an oxygen sensor?
An oxygen sensor specific wrench or socket is highly recommended, as it allows you to get around the wiring harness and apply sufficient torque.
What if replacing the sensor doesn't fix the code?
If the code persists after replacing the sensor, the issue might be in the wiring harness (open/short circuit), a blown fuse, or less commonly, the PCM. Further electrical diagnosis would be required.