P0156 The oxygen sensor after the catalytic converter on bank 2 (sensor 2) has a circuit fault

O2 sensor circuit malfunction, bank 2 sensor 2

Monitor

An oxygen sensor circuit fault mostly affects emissions and fuel economy, and TroubleCodes.net reports little or no drivability change, so book a repair rather than stopping.

Source: how we rate severity

P0156 in short

P0156 means the downstream oxygen sensor on bank 2, the side without cylinder 1, has a circuit malfunction. Common causes are a worn sensor or damaged wiring. The car usually drives normally, so book a check; fix any fuel metering or exhaust leak codes first.

The downstream sensor sits after the catalytic converter and helps the computer check that the converter works. P0156 sets when the signal from bank 2 sensor 2 is outside what the computer expects.

Bank 2 is the side of the engine that does not have cylinder 1; a four-cylinder inline engine has no bank 2.

TroubleCodes.net says to resolve air/fuel metering or exhaust leak codes before diagnosing P0156.

Most likely causes

These are general causes for this code across vehicles. None is specific to one make or model.

  1. Worn or fouled downstream oxygen sensor

    Common general cause
    Why it ranks here
    TroubleCodes.net lists defective or fouled sensors among the causes.
    What would change this
    Deposits on the removed sensor or readings out of range raise it.
    How to test the oxygen (o2) sensor

  2. Damaged, corroded or disconnected wiring or connector

    Common general cause
    Why it ranks here
    TroubleCodes.net lists wiring and connector damage, open circuits and blown fuses.
    What would change this
    Visible damage or failed continuity tests raise it.

  3. Other fuel metering or exhaust leak problem

    Possible — needs testing
    Why it ranks here
    TroubleCodes.net says to fix air/fuel metering or exhaust leak codes first.
    What would change this
    Other fuel or exhaust codes stored with it raise this.

What to test first

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

  1. Read all codes and freeze-frame data and note any fuel trim, misfire, exhaust or other oxygen sensor codes stored with P0156

    Low riskTool: OBD-II scan tool

    • IfFuel trim, misfire or other sensor codes are also stored

      It meansRepair those first; they can disturb this sensor.

      Go to step 2

    • IfP0156 is the only code

      It meansInspect the sensor wiring next.

      Go to step 2

  2. With the exhaust cold, inspect the sensor wiring, connector and related fuses for damage, corrosion and routing near hot parts

    Use cautionTool: visual inspection

    Warning:Let the exhaust cool fully before touching the sensor or its wiring. Back-probe connectors gently, never pierce insulation, and follow the wiring diagram for your engine.

  3. Unplug the sensor and test its resistance and the circuit continuity, voltage and ground against the specification for your engine

    Best left to a shopTool: digital multimeter; wiring diagram

    Warning:Let the exhaust cool fully before touching the sensor or its wiring. Back-probe connectors gently, never pierce insulation, and follow the wiring diagram for your engine.

Symptoms

  • Check engine light
  • Reduced fuel economy
  • Hesitation or rough idle in some cases

How to fix

  1. With the exhaust cold, inspect the sensor wiring and connector for damage and routing near hot exhaust parts, then clear the code and drive through several cycles.

Parts and cost context

  • Oxygen (O2) sensor:Use the correct sensor for that bank and position on your engine; sensors in different positions are often different parts.

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

Compare used part prices on PartPriceGuide

On your vehicle

Toyota

  • 2003–2004 · 4Runner

    Supported by vehicle data

    Toyota bulletin 00505 covers a MIL on with P0136 and/or P0156 (oxygen sensor circuit) on 2003-2004 4Runner. Whether it is still current is not verified.

  • 2004–2005 · Land Cruiser

    Supported by vehicle data

    Toyota bulletin 04605 is an ECM calibration update for a MIL on with P0136 and/or P0156 on 2004-2005 Land Cruiser. Whether it is still current is not verified.

  • 00505Status unverified

    MIL on with P0136 and/or P0156 (oxygen sensor circuit)

    2003–20044runner · issued · NHTSA 10015535

    Toyota bulletin for 2003-2004 4Runner with the MIL on and P0136 and/or P0156 stored, described as an oxygen sensor circuit condition. Only the NHTSA summary was read; it does not give the repair.

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

  • 04605Status unverified

    ECM calibration update for MIL on with P0136 and/or P0156

    2004–2005land-cruiser · issued · NHTSA 10017641

    Toyota bulletin titled as an ECM calibration update for a MIL on with P0136 and/or P0156 on 2004-2005 Land Cruiser. Only the NHTSA summary was read; it does not give the repair.

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

Lexus

  • 2004–2005 · LX

    Supported by vehicle data

    Lexus bulletin 01606 is an ECM calibration update for a MIL on with P0136 and/or P0156 on 2004-2005 LX 470. Whether it is still current is not verified.

  • 01606Status unverified

    ECM calibration update for MIL on with P0136 and/or P0156

    2004–2005lx · issued · NHTSA 10017661

    Lexus bulletin titled as an ECM calibration update for a MIL on with P0136 and/or P0156 on 2004-2005 LX 470. Only the NHTSA summary was read; it does not give the repair.

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

Ford

  • 2001–2002 · Windstar

    Supported by vehicle data

    Ford bulletin 15872 covers P0156 (HO2 / catalyst monitor sensor circuit failure) and names contamination, on 2001-2002 Windstar. Whether it is still current is not verified.

  • 1999 · Mustang

    Supported by vehicle data

    Ford bulletin 8043 covers a check engine lamp with P0136, P0141, P0156 and P0161 on some 1999 Mustang with the 4.6L 2V engine. Whether it is still current is not verified.

  • 15872Status unverified

    P0156 catalyst monitor sensor circuit failure from contamination

    2001–2002windstar · issued · NHTSA 637728

    Ford bulletin on P0156 (HO2 / catalyst monitor sensor circuit failure) with contamination named as the subject, on 2001-2002 Windstar. Only the NHTSA summary was read; it does not give the repair.

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

  • 8043Status unverified

    Check engine lamp with P0136, P0141, P0156 and P0161 on 4.6L 2V

    1999mustang · issued · NHTSA 612243

    Ford bulletin for some 1999 Mustang with the 4.6L 2V engine showing the check engine lamp with P0136, P0141, P0156 and P0161. Only the NHTSA summary was read; it does not give the repair.

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

No curated relationships for P0156 yet.

All Oxygen sensors codes

Sources and review

  1. P0156 trouble code page — TroubleCodes.net
  2. On-Board Diagnostic Trouble Codes (generic code title list) — Delaware Division of Motor Vehicles
  3. Toyota bulletin 00505: MIL on with P0136 and/or P0156 (oxygen sensor circuit) — Toyota (filed with NHTSA) ,
  4. Toyota bulletin 04605: ECM calibration update for MIL on with P0136 and/or P0156 — Toyota (filed with NHTSA) ,
  5. Lexus bulletin 01606: ECM calibration update for MIL on with P0136 and/or P0156 — Toyota (filed with NHTSA) ,
  6. Ford bulletin 15872: P0156 catalyst monitor sensor circuit failure from contamination — Ford Motor Company (filed with NHTSA) ,
  7. Ford bulletin 8043: Check engine lamp with P0136, P0141, P0156 and P0161 on 4.6L 2V — Ford Motor Company (filed with NHTSA) ,
Last reviewed
Written by
Saurabh K.
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