OBD-II Fault Code

P0155: O2 Sensor Heater Circuit Malfunction (Bank 2 Sensor 1)

Meaning, symptoms, likely causes, diagnostic checks and repair guidance for P0155.

System family

Powertrain

Generic/SAE

Repair category

Oxygen sensor / heater

Use this category to narrow your checks before replacing parts.

Severity

Medium

Severity is a general guide. Confirm with scan-tool data and vehicle symptoms.

What P0155 usually means

O2 Sensor Heater Circuit Malfunction (Bank 2 Sensor 1).

Common symptoms

Check Engine light; Poor drivability or reduced fuel economy depending on fault; Fuel economy may drop

Likely causes

Faulty O2 sensor; Heater circuit fuse/wiring fault; Exhaust leak; Engine running too rich/lean

Diagnostic checks

Scan all modules and record freeze-frame data before clearing codes; Check battery voltage and related fuses; Inspect O2 sensor wiring near exhaust heat; Check heater power/ground and sensor response before replacement

Repair guidance

Repair wiring/fuse/exhaust leak or replace confirmed faulty oxygen sensor

Verification after repair

Clear code, road-test through the same drive condition, then rescan

Note: Confirm vehicle make/model/year because manufacturer-specific codes can vary. A DTC identifies a circuit or system condition, not always the failed part.