P0155 — O2 Sensor Heater Circuit (Bank 2 Sensor 1)

Quick answer

• What the P0155 code means: The P0155 code indicates a malfunction in the heater circuit of the oxygen sensor located in Bank 2, Sensor 1 position.
• Severity: This is a moderately severe code. You can likely drive your car home, but it's recommended to address it relatively soon to prevent further issues and reduced fuel economy.
• Most common cause: A failed oxygen sensor heater element.

What the P0155 code means

The P0155 diagnostic trouble code (DTC) officially stands for "O2 Sensor Heater Circuit (Bank 2 Sensor 1)." In simpler terms, this code signifies that the powertrain control module (PCM) has detected an electrical fault within the heating element of the upstream oxygen sensor on engine bank 2. "Bank 2" refers to the side of the engine that does not contain cylinder #1, while "Sensor 1" designates the oxygen sensor located before the catalytic converter (upstream sensor). These upstream sensors are crucial for monitoring the oxygen content in the exhaust gases, which the PCM uses to adjust the air-fuel mixture for optimal combustion and emissions control. The heating element within the sensor quickly brings it up to its operating temperature, allowing for accurate readings soon after engine start-up. When the heater circuit fails, the sensor takes longer to warm up, compromising its ability to send accurate data to the PCM, leading to a less efficient engine operation and potentially increased emissions.

Common symptoms

• Check Engine Light (CEL) illuminated: This is almost always the first and most obvious symptom.
• Decreased fuel economy: The PCM may not be able to precisely control the air-fuel mixture, leading to more fuel consumption.
• Rough idle or hesitation: Incorrect air-fuel ratio can cause the engine to run less smoothly.
• Engine performance issues: The engine might feel sluggish or lack power.
• Failed emissions test: Due to increased emissions from an improperly controlled air-fuel mixture.

Common causes

1. Failed oxygen sensor heater element (most likely): Over time, the heating element inside the oxygen sensor can burn out or short internally.
2. Wiring harness issues: Damaged, corroded, shorted, or open wiring leading to the O2 sensor heater circuit. This can include rodent damage, chafing, or corrosion at the connector.
3. Blown fuse: A dedicated fuse protects the O2 sensor heater circuit in some vehicles. If this fuse blows, it will cut power to the heater.
4. Faulty oxygen sensor connector: Corrosion or damage at the electrical connector to the O2 sensor.
5. PCM failure (least likely): Rarely, an internal fault within the PCM itself can cause this code, but it