P0155 O2 Sensor Heater Circuit Malfunction Bank 2 Sensor 1

P0155 points to a heater-circuit malfunction for bank 2 sensor 1. The upstream oxygen or air-fuel sensor heater did not pass its circuit or warm-up monitor.

Code details

Generic OBD-II · P0

System: Fuel / Air
Code type: Generic (SAE / ISO controlled)
Standard: SAE J2012 / ISO 15031-6

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not confuse a heater-circuit code with a mixture-reading code; the fault path starts with heater power, control, and wiring.

Symptoms of P0155

Check-engine light on, sometimes with rough or uneven running.
Hesitation, surging, or a noticeable change in fuel economy.
Occasionally hard starting or a smell of unburnt fuel.

Common causes of P0155

A failing or contaminated sensor (MAF, MAP, oxygen or air-fuel sensor).
Intake or vacuum leaks, or an exhaust leak near an upstream sensor.
Wiring, connector, or fuel-delivery problems that skew the reading.

Useful checks before replacing parts

Check heater power, ground or control, fuse condition, connector damage, and harness routing near hot exhaust parts.
Measure heater resistance or current only with the correct service information and temperature conditions.
Look for other sensor-heater codes that may share a fuse, relay, or ground path.

Related OBD-II codes

These nearby fuel / air entries can help compare wording and pin down the fault area.