P0155🌫 Emissions / oxygen sensorsDrive with caution, fix soon

P0155: O2 Sensor Heater Circuit, Bank 2 Sensor 1 (Meaning, Causes, Fixes)

Reviewed 2026-10-22 · Based on 2 cited source(s)

What P0155 means

Bank 2 Sensor 1 is the upstream oxygen sensor, before the catalytic converter, on the side of a V6, V8 or V10 engine that does not contain cylinder 1. The sensor only reads accurately once it's hot, so it has a built-in electric heater that brings it up to temperature quickly and lets the engine enter closed-loop fuel control sooner. OBD-Codes.com explains that the engine computer times how long the sensor takes to start switching after a cold start; if too much time passes (judged against coolant temperature), it sets P0155. RepairPal says the code sets when the PCM detects the heater isn't operating, and its technical section describes the same timing test: after the coolant temperature shows the engine has warmed up, the PCM measures how long the sensor takes to start switching above and below about 450 millivolts. RepairPal adds that the code usually needs the fault on two drive cycles, but can set in under fifteen minutes if the problem is severe, and that the exact setting criteria vary by vehicle. One RepairPal line describes P0155 as the sensor signal staying at or near 0.10 volt, which reads more like a signal fault than a heater fault; the rest of both sources describe a heater-circuit fault, so this page follows that. P0135 is the same fault on bank 1.

Severity: can I keep driving?

Drive with caution, fix soon

Usually drivable, and often the only things you'll notice are the check engine light and somewhat worse fuel economy. RepairPal rates P0155 Moderate: not an immediate threat to safety or the car, but get it diagnosed within a reasonable time. Until the upstream sensor on bank 2 warms up and works, the engine can't fine-tune its fuel mixture on that side, and RepairPal notes the car may fail an emissions test.

Common symptoms

Likely causes

Roughly most to least common, based on the sources below. Your vehicle may differ.

  1. Heater element inside the oxygen sensor has high resistance, an internal open, or an internal short (OBD-Codes.com); RepairPal lists a defective oxygen sensor
  2. Heater circuit wiring with high resistance, an open, or a short to ground in the harness (OBD-Codes.com)
  3. Faulty oxygen sensor wiring or connections (RepairPal)

Diagnostic steps you can do

⚠ Before you start

Work on a cool engine, parked on level ground with the parking brake set. Never work under a car supported only by a jack.

  1. Read all stored codes and freeze-frame data. If P0155 shows up with other O2 heater codes at the same time (such as P0135, P0141 or P0161), check a shared fuse, relay or power feed before replacing sensors.
  2. Find the Bank 2 Sensor 1 oxygen sensor (upstream, before the catalytic converter, on the side of the engine without cylinder 1) and inspect its wiring and connector for melted insulation, chafing against the exhaust, corrosion or a loose plug.
  3. Check the fuse that feeds the oxygen sensor heaters (see your owner's or service manual for its location).
  4. With a multimeter, measure the heater resistance across the sensor's heater terminals and compare it to your vehicle's specification. An open circuit or a reading far out of spec means the sensor needs replacing.
  5. With the key on, check for battery voltage on the heater power wire at the harness side of the connector.

Typical fixes

Repair costs vary widely by vehicle, region, parts brand and shop, so we don't quote prices. Get a written estimate after diagnosis.

🛠 When to call a pro

  • The code comes back after a new sensor is fitted. Several owners on OBD-Codes.com's forums replaced the sensor and still had P0155, which usually points to wiring, power, a relay or the computer
  • The sensor is seized in the exhaust and won't come out without heat or special tools
  • You need wiring diagrams to trace the heater power and ground
  • RepairPal lists two common misdiagnoses: replacing the front catalytic converter when the oxygen sensor is at fault, and replacing the oxygen sensor when the wiring or connection is at fault

Where to buy

Plain search links. Always match parts to your exact year, make, model and engine.

OBD2 scanners on Amazon Parts at Advance Auto Parts catalog at RockAuto

FAQs

Can I drive with P0155?

Usually yes. RepairPal rates it Moderate, and OBD-Codes.com says you'll most likely notice poor fuel economy and the check engine light. Get it fixed reasonably soon, especially before an emissions inspection.

What's the difference between P0135 and P0155?

They are the same heater-circuit fault on different sides of the engine. P0135 is the upstream sensor on bank 1 (the side with cylinder 1), and P0155 is the upstream sensor on bank 2.

Do I just need a new oxygen sensor?

Often, but not always. A failed heater inside the sensor can't be repaired, yet both sources also list wiring and connection faults, and RepairPal warns that replacing the sensor when the wiring is at fault is a common misdiagnosis. Test the heater resistance and the circuit first.

How much does it cost to fix P0155?

Neither source gives a repair cost for P0155. It depends on whether you need a wiring repair, a fuse or a new oxygen sensor, so get the circuit tested first.

Sources

  1. OBD-Codes.com: P0155 O2 Sensor Heater Circuit Malfunction (B2S1)
  2. RepairPal: P0155 O2 Sensor Heater Circuit (rated Moderate)

Last reviewed 2026-10-22. Code definitions and repair steps can vary by manufacturer. Confirm with your vehicle's service information.