P0155
O2 Sensor Heater Circuit Malfunction (Bank 2 Sensor 1)
Encountering the engine check light code P0155 signifies an explicit mechanical or electrical operational breakdown categorized as "O2 Sensor Heater Circuit Malfunction (Bank 2 Sensor 1)". Professional scanner tools usually flag this subsystem loop early on.
Driver's Summary
The diagnostic trouble code P0155 indicates an active fault in the o2 sensor heater circuit malfunction (bank 2 sensor 1) circuit or component. You may notice check engine light, longer engine warm-up time, all of which are direct consequences of this malfunction. This is a low-urgency fault with minimal immediate impact on safety, but it should be resolved before your next emissions test.
Symptoms
Check engine light, longer engine warm-up time
Common Causes
- Blown O2 sensor heater fuse
- Failed internal O2 sensor heater element
- Corroded O2 sensor connector
- Open circuit in wiring harness
How to Fix
- 1 Check and replace blown fuses
- 2 Replace Bank 2 Sensor 1 O2 sensor
- 3 Clean and apply dielectric grease to connector
- 4 Repair broken wiring
Technical Explanation
To set P0155, the PCM samples the affected circuit multiple times per second, comparing live readings against manufacturer-programmed operating windows. Sensor output is cross-validated against complementary sensor data (such as MAF vs. MAP correlation, or upstream vs. downstream O2 comparison) to confirm the fault is genuine and not a result of a sensor reading an actual engine condition. After two failed drive cycles, the code transitions from a pending to a confirmed DTC, and the PCM activates the MIL. Clearing the code without repairing the fault will result in re-illumination within one to two complete drive cycles.
Is It Safe to Drive?
Code P0155 has minimal impact on immediate driving safety. However, the underlying blown o2 sensor heater fuse issue will cause this vehicle to fail an emissions inspection and may gradually affect fuel economy if left unrepaired.
Mechanic's Pro Tip
The most common mistake with P0155 is replacing the sensor without verifying the reference voltage and ground integrity first. Use a scan tool to monitor the sensor's live output; a truly failed sensor shows a stuck, flatlined reading — a sensor that fluctuates but reads slightly off usually indicates a wiring or vacuum issue, not a dead sensor. Always spray electrical contact cleaner on the connector pins before condemning the sensor.
Fuse: $10; O2 Sensor replacement: $150 - $300