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P0155 O2 Sensor Heater Circuit Malfunction (Bank 2 Sensor 1)
What it means
Oxygen sensors have a built-in heater so they start working quickly after a cold start. The computer found a problem in the heater circuit of the upstream sensor on bank 2 (the side of a V6/V8 without cylinder 1). This code only appears on engines with two banks.
Severity: Low to Moderate
Can I drive it? Safe to drive in the short term. Expect slightly worse fuel economy and higher emissions, especially right after a cold start, and you may fail an emissions test.
Common causes (most likely first)
- Burned-out heater element inside the oxygen sensor (most common)
- Blown fuse for the O2 sensor heater circuit
- Damaged wiring or corroded connector
- Faulty O2 heater relay (some vehicles)
Likely fixes
- Check the O2 heater fuse
- Measure heater resistance at the sensor connector (out of spec means a bad sensor)
- Repair any damaged wiring
- Replace the bank 2 sensor 1 oxygen sensor
DIY parts cost
$40–$150
Approximate estimate
Shop repair cost
$150–$400
Approximate estimate, parts + labor
DIY difficulty
Easy to Moderate
Varies by vehicle
Cost ranges are rough, approximate U.S. estimates and vary widely by vehicle, region, and parts brand. Always confirm the diagnosis before buying parts.
Parts you may need
- Upstream oxygen sensorCheck price
- O2 sensor socketCheck price
- Anti-seize compoundCheck price
- FusesCheck price
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