O2 Sensor Heater Circuit Malfunction (Bank 2 Sensor 1)
The P0155 code indicates a malfunction in the heater circuit of the oxygen sensor located before the catalytic converter on Bank 2 (the side of the engine not containing cylinder #1). The heater element is essential for the sensor to reach operating temperature quickly, especially during cold starts. When the powertrain control module (PCM) detects an abnormal current draw or resistance in the heater circuit, it sets this code. This can lead to inaccurate air-fuel ratio readings, reduced fuel economy, and increased emissions.
01. Most Common Causes
- Faulty oxygen sensor (Bank 2 Sensor 1)
- Blown heater circuit fuse
- Open or shorted wiring in the heater circuit
- Damaged connector or poor electrical connection
- Failed PCM (rare)
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Poor fuel economy
- Failed emissions test
- Rough idle or hesitation
- Possible sulfur smell from exhaust
03. Step-by-Step Diagnosis
Step 1: Scan for codes and record freeze frame data.
Step 2: Visually inspect the O2 sensor wiring and connector for damage, corrosion, or loose connections.
Step 3: Check the heater circuit fuse and replace if blown.
Step 4: Using a multimeter, measure resistance of the heater element (typically 2-10 ohms) and compare to specifications.
Step 5: Test for battery voltage and ground at the sensor connector with key on engine off.
Step 6: If all tests pass, replace the oxygen sensor.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
You can drive short distances, but it may cause poor fuel economy and increased emissions. Prolonged driving can damage the catalytic converter.
How much does it cost to fix?▼
Typically $150-$300 for parts and labor, depending on vehicle and shop rates.