P0155 Heater circuit fault on the upstream oxygen sensor on the second bank of cylinders (bank 2, sensor 1)

O2 sensor heater circuit malfunction, bank 2 sensor 1

Monitor

The heater only brings the sensor up to working temperature faster, so a fault mostly shows up as the light and a failed emissions test; TroubleCodes.net says you will probably not notice a change in how the car drives.

Source: how we rate severity

P0155 in short

P0155 means the computer found a fault in the heater circuit of the first oxygen sensor on bank 2, the cylinder bank without cylinder 1. The usual causes are a burnt-out sensor heater or a wiring fault. It is normally safe to drive, but it will fail an emissions test until it is fixed.

An upstream oxygen sensor has a small heater so it reaches working temperature soon after the engine starts. The computer powers the heater and checks the circuit. If the circuit is open, shorted, or the element has the wrong resistance, it sets P0155 for the sensor on the second cylinder bank.

Because the heater only speeds up warm-up, the engine usually keeps running normally and the only sign is the check engine light. The sensor can still read once it has warmed from exhaust heat, but the computer spends longer in a fixed-fuel mode and emissions can rise.

Several carmakers have bulletins that name P0155 together with P0135, the matching heater code on bank 1. Some point to computer calibration, some to wrong or newly fitted sensors and harnesses, so check for a bulletin before buying a sensor.

Most likely causes

  1. Burnt-out or high-resistance heater in the oxygen sensor

    Common general cause
    Why it ranks here
    TroubleCodes.net lists a heater element with high resistance or an open circuit as a main cause, and a 2001 Toyota Sequoia owner reports a sensor replacement for P0155.
    What would change this
    Rises if the heater pins on the sensor connector read open or out of specification with an ohmmeter. Falls if the heater resistance is in specification and power and ground reach the connector.
    How to test the oxygen (o2) sensor

  2. Power or ground fault in the heater wiring or connector

    Common general cause
    Why it ranks here
    The same reference says problems on the power side or the ground side of the heater circuit also set the code, so the wiring is tested before the sensor.
    What would change this
    Rises if the connector shows no battery voltage on the power pin or a poor ground when tested. Falls if both are present and steady.
    How to test the oxygen (o2) sensor

  3. Engine computer calibration that sets the code (some models)

    Supported by vehicle data
    Why it ranks here
    Ford's 1998 Taurus and Sable bulletin attributes P0135 or P0155 to the computer calibration. Toyota's Tundra and Sequoia bulletin names the codes in the engine control module. The summaries are unverified.
    What would change this
    Rises if the vehicle is in a bulletin range and the computer is not at the latest calibration. Falls if the software is current or the heater tests bad.
    How to test the engine control module (ecm / pcm)

  4. Wrong sensor or harness, or a fault after a sensor swap (some models)

    Supported by vehicle data
    Why it ranks here
    GM bulletins name incorrect O2 sensors and wiring harness on 2004 trucks, and intermittent P0135 and P0155 after sensor replacement on 2004 Cadillacs.
    What would change this
    Rises if the code began right after a sensor was replaced or if the sensor part number does not match the vehicle. Falls if the original sensor is still fitted.
    How to test the oxygen (o2) sensor

What to test first

Start at step 1. Each result tells you what it means and where to go next.

  1. Read all stored codes. Note whether P0135 (bank 1 heater) or other oxygen sensor codes are stored with P0155, and whether the code returned right after a sensor was replaced.

    Low riskTool: OBD-II scan tool

  2. Ask a dealer whether your VIN has an engine computer update or bulletin for P0155.

    Low risk

  3. Unplug the bank 2 sensor 1 connector, then use the wiring diagram to find the heater pins and check for battery voltage on the power pin and a good ground on the control side.

    Use cautionTool: digital multimeter, wiring diagram

    Warning:The exhaust is very hot after driving, so let it cool before reaching near the sensor, and keep meter leads away from the fan and belts. Use the diagram so you probe the heater pins, not the signal pins.

  4. With the sensor unplugged, measure resistance across the two heater pins on the sensor side and compare it with the specification in the service information.

    Use cautionTool: digital multimeter

    Warning:Do this with a cold exhaust and the engine off. A sensor that has been in the exhaust can seize in its fitting, and forcing it can damage the exhaust manifold or pipe.

Symptoms

  • Check engine light on with no change in how the car drives
  • Failed emissions test
  • Slightly worse fuel economy, which TroubleCodes.net says is rarely noticeable

How to fix

  1. Check whether your VIN has an open engine computer update or bulletin for P0155 before buying a sensor.

  2. With the engine off and cool, look over the wiring and connector at the bank 2 front oxygen sensor for damage, melting or corrosion.

    Warning:Keep wiring away from the hot exhaust and moving parts; do not unclip anything that is hot.

Parts and cost context

  • Oxygen (O2) sensor:The heater is part of the sensor, so a failed heater means a new sensor. Use the exact part for the bank and position, and ask about labor; get a quote.

Labor varies by vehicle and shop; get a quote before you approve a repair.

Compare used part prices on PartPriceGuide

On your vehicle

Toyota

  • 2001–2002 · Sequoia

    Supported by vehicle data

    Toyota bulletin 01902R names P0135 and P0155 on 2000-2002 Tundra and Sequoia. A 2001 Sequoia owner reports P0155 at about 77,000 miles and a sensor replacement. Whether the bulletin is still current is not verified.

  • 01902RStatus unverified

    MIL on with P0135 and/or P0155 in the engine control module

    2000–2002tundra, sequoia · NHTSA 10005823

    Names P0135 and P0155 as the reason for the light. The NHTSA summary does not say what the repair is.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

Ford

  • 1998 · Taurus

    Supported by vehicle data

    Ford bulletin 12515 attributes P0135 or P0155 on the 1998 Taurus to the PCM calibration. Whether it is still current is not verified.

  • 2012 · Expedition

    Possible — needs testing

    Ford TSB 13-5-7 names P0135 and P0155 on the 2012 Expedition. The summary does not give a repair.

  • 12515 (ford)Status unverified

    P0135 or P0155 caused by PCM calibration

    1998taurus · NHTSA 605276

    Attributes the codes to the powertrain control module calibration.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

  • TSB-13-5-7 (ford)Status unverified

    MIL on with P0135, P0155 and possibly P0030, P0050, P0053, P0059, P0141, P0161

    2012expedition · NHTSA 10052769

    Names the codes only; the NHTSA summary does not say what the repair is.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

Mercury

  • 12515 (mercury)Status unverified

    P0135 or P0155 caused by PCM calibration

    1998sable · NHTSA 605276

    Attributes the codes to the powertrain control module calibration.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

Chevrolet

  • 2004 · Silverado 1500

    Supported by vehicle data

    GM bulletin 3322 links heater circuit codes including P0155 to incorrect O2 sensors and wiring harness on 2004 full-size trucks. Whether it is still current is not verified.

  • 3322 (chevrolet)Status unverified

    Incorrect O2 sensors and wiring harness causing heater circuit codes

    2004silverado-1500, suburban, tahoe · NHTSA 10017196

    Names incorrect oxygen sensors and a wiring harness as the cause of P0135, P0141, P0155 and P0161.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

GMC

  • 3322 (gmc)Status unverified

    Incorrect O2 sensors and wiring harness causing heater circuit codes

    2004sierra-1500, yukon · NHTSA 10017196

    Names incorrect oxygen sensors and a wiring harness as the cause of P0135, P0141, P0155 and P0161.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

Cadillac

  • 2004 · Deville

    Supported by vehicle data

    GM bulletin 01819 covers intermittent P0135 and P0155 that set after an oxygen sensor replacement.

  • 01819Status unverified

    Intermittent P0135, P0155 after oxygen sensor replacement

    2004deville · NHTSA 10007517

    Covers intermittent P0135 and P0155 that set after an oxygen sensor was replaced. The summary does not give the fix.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

  • P0135The heater in the upstream oxygen sensor on bank 1 isn't working as the computer expects

    Other bank Supported by vehicle data

    P0135 is the same heater circuit fault on bank 1 sensor 1. Several bulletins name P0135 and P0155 together.

All Oxygen sensors codes

P0155 questions

Which side is bank 2 sensor 1?

Bank 2 is the cylinder bank that does not hold cylinder 1, and sensor 1 is the one before the catalytic converter. Check your service information for which exhaust side that is on your engine.

Can I keep driving with P0155?

Usually yes. The heater affects warm-up and emissions rather than driving, but the code will fail an emissions test until it is fixed.

Sources and review

  1. P0155 heated oxygen sensor 1, bank 2, heater control circuit malfunction — TroubleCodes.net
  2. NHTSA complaint ODI 10197455, 2001 Toyota Sequoia: P0155 read as oxygen sensor failure — NHTSA
  3. Ford 12515: P0135 or P0155 caused by PCM calibration (1998 Taurus and Sable) — Ford Motor Company
  4. Toyota 01902R: MIL on with P0135 and/or P0155 (2000-2002 Tundra and Sequoia) — Toyota Motor Corporation
  5. GM 3322: incorrect O2 sensors and wiring harness causing heater circuit codes P0135, P0141, P0155, P0161 (2004 trucks) — General Motors
  6. GM 01819: intermittent P0135, P0155 set after oxygen sensor replacement (2004 Cadillac) — General Motors
  7. On-Board Diagnostic Trouble Codes (generic code title list) — Delaware Division of Motor Vehicles
  8. Ford TSB 13-5-7: MIL on with P0135, P0155 and possible P0030, P0050, P0053, P0059, P0141, P0161 (2012 Expedition and Navigator) — Ford Motor Company
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Written by
Saurabh K.
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