P0140 The oxygen sensor behind the catalytic converter on bank 1 is not sending a signal the computer can use

O2 sensor circuit no activity detected, bank 1 sensor 2

Monitor

The sensor behind the converter mainly watches converter health. A Ford bulletin for this code covers cars with no driveability concerns, so you can usually drive while you book a check.

It gets more serious if:

  • Inspect soon: Inspect soon if the engine runs rough, hesitates or loses power, or the light flashes. Another fault is likely behind it.

Source: how we rate severity

P0140 in short

P0140 means the oxygen sensor behind the catalytic converter on bank 1 is sending no usable signal. A faulty sensor, damaged heater or signal wiring, or a blown fuse are the usual causes. It is usually drivable, but have it checked and the sensor tested before you replace anything.

The oxygen sensor after the converter lets the computer check whether the converter is working. P0140 sets when that sensor stays flat and shows no activity.

The sensor, its heater circuit or signal wiring are the usual causes, and so are a blown fuse that feeds the heater. TroubleCodes.net also lists engine deposits from additives and, rarely, the computer.

Nissan and Infiniti have bulletins for rear sensor codes P0138 to P0140 and P0158 to P0160 on late-1990s and early-2000s models, Kia has an engine computer update for the 2009 Rio, and GM has a bulletin for 2013 Sierra and Silverado trucks where a bent connector terminal set P0140 with P2270.

Most likely causes

  1. Downstream oxygen sensor, bank 1

    Common general cause
    Why it ranks here
    TroubleCodes.net lists a defective sensor and says to replace it if resistance is outside the maker specification.
    What would change this
    Rises if the sensor shows flat voltage and tests out of range. Falls if the sensor and wiring both test good.
    How to test the oxygen (o2) sensor

  2. Heater or signal wiring, connector or fuse

    Common general cause
    Why it ranks here
    TroubleCodes.net lists damaged heater or signal wiring and blown fuses. A GM bulletin found a bent terminal at connector X131 setting P0140 with P2270 on 2013 Sierra and Silverado trucks.
    What would change this
    Rises if the harness is damaged, a fuse is blown or a terminal is bent. Falls if the circuit tests good.

  3. Engine computer software (some models)

    Supported by vehicle data
    Why it ranks here
    Kia TSB-033 is an engine computer upgrade for the 2009 Rio with P0140 among the codes. Nissan bulletins for the Maxima and Pathfinder cover P0138 to P0140 but the summaries do not give the repair.
    What would change this
    Rises on these vehicles if a dealer finds a bulletin applies. Falls if it does not.
    How to test the engine control module (ecm / pcm)

  4. A different engine fault affecting the rear sensor

    Possible — needs testing
    Why it ranks here
    Other codes such as P2270 (GM) or misfire and cold-start codes (Kia) were stored with P0140 in the bulletins, so the sensor may not be the root cause.
    What would change this
    Rises if other codes are stored with P0140. Falls if P0140 is the only code.

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 related rear-sensor codes (P0137, P0138, P0139, P0141) and other engine codes.

    Low risk

    • IfP2270 or other related codes are stored

      It meansCheck the connector terminals and bulletins for your vehicle.

      Go to step 2

    • IfP0140 is the only code

      It meansInspect the wiring and fuse for the sensor.

      Go to step 2

  2. With the engine off and cool, check the sensor connector and harness behind the converter for damage, bent terminals or a blown heater fuse.

    Use cautionTool: flashlight, multimeter

    Warning:Exhaust parts stay hot long after the engine is off. Work only on a cold engine.

  3. Test the sensor resistance, voltage and continuity against the maker specification, and ask a dealer about a computer update for your VIN.

    Best left to a shopTool: multimeter, scan tool

    Warning:Probe only the circuits the service manual names; a wrong probe can damage the computer.

Symptoms

  • Check engine light and often no other change in how the car drives
  • Slightly worse fuel economy
  • Rough running, hesitation or a flashing light Gets more serious: stop and have it checked.

How to fix

  1. With the engine off and cool, check the sensor connector and fuse for the oxygen sensor heater.

  2. Ask a dealer whether your VIN has an open bulletin or computer update for P0140.

Parts and cost context

  • Oxygen (O2) sensor:Test the sensor before replacing it; a harness or fuse fault can look the same. Labour varies; 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

Kia

  • 2009 · Rio

    Supported by vehicle data

    Kia TSB-033 is an engine computer upgrade for the check engine light with P0140 and other codes. Whether it is still current is not verified.

  • TSB-033Status unverified

    ECM upgrade, MIL on with P0300, P0128, P0140, P0442 and P0461

    2009rio · NHTSA 10032713

    Engine computer software upgrade for rough idle during cold start and the check engine light.

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

Nissan

  • 1999–2000 · Pathfinder

    Supported by vehicle data

    Nissan NTB01-048A covers rear oxygen sensor codes including P0140. Whether it is still current is not verified.

  • NTB01016AStatus unverified

    MIL on with rear O2 sensor codes P0138-P0140 or P0158-P0160

    2000–2001maxima · NHTSA 623204

    Service information for rear oxygen sensor codes. The NHTSA summary does not give the repair.

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

  • NTB01048AStatus unverified

    MIL on with rear O2 sensor codes P0138-P0140 or P0158-P0160

    1999–2000pathfinder · NHTSA 630793

    Service information for rear oxygen sensor codes. The NHTSA summary does not give the repair.

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

Infiniti

  • 2000–2001 · I30

    Supported by vehicle data

    Infiniti ITB01-011A covers rear oxygen sensor codes including P0140. Whether it is still current is not verified.

  • 1999–2000 · QX4

    Supported by vehicle data

    Infiniti ITB01-045 covers rear oxygen sensor codes including P0140. Whether it is still current is not verified.

  • ITB01011AStatus unverified

    MIL on with rear O2 sensor codes P0138-P0140 or P0158-P0160

    2000–2001i30 · NHTSA 623194

    Service information for rear oxygen sensor codes. The NHTSA summary does not give the repair.

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

  • ITB01045Status unverified

    MIL on with rear oxygen sensor codes P0138, P0139, P0140, P0158, P0159, P0160

    1999–2000qx4 · NHTSA 621950

    Service information for rear oxygen sensor codes. The NHTSA summary does not give the repair.

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

  • P0141The heater in the downstream oxygen sensor on bank 1 isn't working as the computer expects

    Same system Supported by vehicle data

    P0141 is the heater circuit fault for the same sensor; Ford and Nissan bulletins list P0140 with the other rear-sensor codes.

  • P0138The downstream oxygen sensor on bank 1 is reporting a voltage that stays too high

    Same system Supported by vehicle data

    P0138 is the high-voltage fault on the same sensor; Nissan bulletins list P0138 to P0140 together.

All Oxygen sensors codes

P0140 questions

Is it safe to drive with P0140?

Usually yes. The sensor mainly checks the converter. Get it checked soon if the car runs rough or the light flashes.

Sources and review

  1. TSB 98-33-04 MIL on with P0140 or P0141 and no driveability concerns — Ford Motor Company
  2. P0140 trouble code summary — TroubleCodes.net
  3. PIP5123 P2270 with P0137-P0140, P013A and P013B — General Motors
  4. TSB-033 ECM upgrade, MIL on with P0300, P0128, P0140, P0442 and P0461 — Kia Motors America
  5. NTB01-016A MIL on with rear O2 sensor codes P0138-P0140 or P0158-P0160 — Nissan North America
  6. NTB01-048A MIL on with rear O2 sensor codes P0138-P0140 or P0158-P0160 — Nissan North America
  7. ITB01-011A MIL on with rear O2 sensor codes P0138-P0140 or P0158-P0160 — Infiniti
  8. ITB01-045 MIL on with rear oxygen sensor codes P0138, P0139, P0140, P0158, P0159, P0160 — Infiniti
Last reviewed
Written by
Saurabh K.
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