Emissions

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

Severity: low Safe to drive

What P0155 means

The engine control unit monitors the current and voltage in the heater circuit of the upstream oxygen sensor on bank 2. The heater brings the sensor up to operating temperature quickly so the ECU can use its signal to control the air-fuel mixture soon after startup. P0155 is set when the circuit is open, shorted, or the heater does not draw the expected current.

Symptoms

  • Check Engine light on
  • Higher fuel consumption
  • Rough idle after a cold start
  • Increased exhaust emissions
  • Failed emissions inspection
  • Oxygen sensor readiness monitor not complete

Possible causes

  1. Failed heater element inside the oxygen sensor
  2. Open or shorted wiring in the heater circuit
  3. Blown heater circuit fuse
  4. Corroded or loose sensor connector
  5. Failed sensor as a whole
  6. Rarely, a faulty heater driver in the PCM

How to diagnose

  1. Scan the codes and freeze frame data, confirm it is bank 2 sensor 1, and look for other codes
  2. Inspect the sensor harness and connector for chafing, heat damage and corrosion
  3. Check the fuse and relay for the oxygen sensor heaters
  4. Measure the heater resistance at the sensor pins and compare to the spec
  5. With ignition on, check for power and the control ground from the PCM at the connector
  6. Test the wires back to the PCM for opens and shorts to ground or power
  7. Check for exhaust leaks near the sensor and review fuel trims
  8. After repair, clear the code and drive the car so the monitor can run

Common fixes

  • Replace the blown fuse (after finding why it blew)
  • Repair the wiring harness or connector
  • Replace the bank 2 sensor 1 oxygen sensor
  • Diagnose, repair or reflash the PCM (rare)

P0155 on different brands

Ford · manuals
On Ford, the extended format P0155:01 used in the 2024-2025 gasoline monitor strategy identifies the condition the monitor detected, not a confirmed failed component.

Questions and answers

Can I drive with a P0155 code?

Yes, usually. It isn't a serious risk to the engine, but fuel economy and emissions can suffer, so get it fixed reasonably soon.

What most often causes P0155?

Most often the heater inside the sensor has failed. Next are damaged wiring, a poor connector contact, or a blown fuse. A PCM fault is uncommon.

What does bank 2 sensor 1 mean?

Bank 2 is the side of the engine that does not contain cylinder 1, and sensor 1 is the one before the catalytic converter. So it is the upstream oxygen sensor on that side.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.