EZCarFix DIY Auto Repair

Diagnostic Trouble Code

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

What it means, how urgent it is, the most likely causes, and the exact order to diagnose it — then pick your vehicle below for model-specific repair guides and parts.

New to check engine lights? Start with our step-by-step diagnosis primer — what to do first, how to get the code read, and when it is safe to drive.

Find P0155 for your vehicle

Pick your make and model for model-specific repair guides, parts, and costs.

What P0155 means

P0155 is the Bank 2 equivalent of P0135: the heater circuit for the Bank 2, Sensor 1 (upstream) oxygen sensor has failed. The internal heater brings the sensor to operating temperature within seconds of startup so fuel control goes closed-loop quickly. The PCM monitors the heater's current draw and sets P0155 when the circuit is open, shorted, or drawing abnormal current. On V6 and V8 engines, Bank 2 is the side opposite cylinder 1. When P0155 appears together with P0135 (Bank 1's heater code), look at what the two banks share — usually a fuse, relay, or power feed — before buying two sensors.

Applies to 29 vehicles across 15 makes.

⚠️ How urgent is it?

Safe to drive; like all heater codes, the sensor works once the exhaust heats it. Expect slightly higher cold-start emissions and a possible small economy penalty on short trips. Repair before your emissions test. If P0135 is present too, check the shared heater fuse and relay first — one blown fuse explains both codes.

Most likely causes

  1. A burned-out heater element in the Bank 2 upstream oxygen sensor — the most common cause.
  2. Heater circuit wiring faults: blown fuse, damaged wires, corroded connector.
  3. Heat-related wiring degradation near the Bank 2 exhaust manifold.
  4. Rarely, a PCM heater-driver issue.

How to diagnose P0155

  1. Check the heater fuse — shared fuses can take out both banks' heaters at once.
  2. Measure heater resistance at the Bank 2 Sensor 1 connector with the sensor unplugged; open circuit condemns the sensor.
  3. Confirm battery voltage at the heater feed wire, key on.
  4. Trace the Bank 2 harness for melted or chafed sections near the manifold.
  5. If both P0135 and P0155 set together, suspect the shared fuse, relay, or power feed before replacing two sensors.

General diagnostic information, not a factory service procedure. If you're unsure, have a qualified technician confirm the diagnosis before buying parts.