P0840 Transmission fluid pressure sensor/switch A circuit fault

Transmission fluid pressure sensor/switch A circuit

Severity not verified — if the car runs badly, have it inspected

We found no source that rates how serious P0840 is on its own.

Source: how we rate severity

P0840 in short

P0840 means the transmission computer sees a fault in the circuit of fluid pressure sensor or switch A, which reports hydraulic pressure inside the transmission. Wiring, the sensor or the module can cause it. We found no severity rating, so have a shop read the module and check the fluid.

A pressure sensor or switch tells the transmission computer whether hydraulic pressure matches what it commanded. If the reading is missing or does not make sense, P0840 sets.

TroubleCodes.net lists wiring, poor connections, the sensor and the module. Nissan has several bulletins for CVT cars: some 2007-2008 Altima, Rogue and Sentra cars need a new control valve assembly, and 2003-2007 Murano and 2009-2010 Cube and Versa have their own.

Ford SSM 50116 lists P0840 among many codes on 2020-2021 Escapes that lose a voltage reference and blow fuse 44.

Most likely causes

  1. Wiring or connector fault in the sensor circuit

    Common general cause
    Why it ranks here
    TroubleCodes.net lists wiring and poor connections, and this is a circuit code.
    What would change this
    Rises if the harness is chafed or the connector is corroded.

  2. Failed pressure sensor or switch

    Common general cause
    Why it ranks here
    TroubleCodes.net lists the sensor.
    What would change this
    Rises if the wiring tests good and the reading is missing or stuck.

  3. Control valve assembly (2007-2008 Altima, Rogue, Sentra CVT)

    Supported by vehicle data
    Why it ranks here
    Nissan NTB09-148 replaces the control valve assembly and has the module relearn calibration, and NTB09-044 ties odd CVT fluid to the code.
    What would change this
    Rises on a covered CVT car, especially with discolored fluid.

  4. Loss of voltage reference (2020-2021 Ford Escape)

    Supported by vehicle data
    Why it ranks here
    Ford SSM 50116 lists P0840 with many codes after a lost reference voltage and a blown fuse 44.
    What would change this
    Rises if many unrelated sensor codes appeared at once.

  5. Transmission control module

    Possible — needs testing
    Why it ranks here
    TroubleCodes.net lists the module.
    What would change this
    Rises only after the sensor, wiring and fluid are ruled out.
    How to test the transmission control module (tcm)

What to test first

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

  1. Read codes from the engine and transmission modules with a scan tool that supports both, before anything is cleared. Note other pressure, CVT or reference-voltage codes.

    Low riskTool: scan tool that reads the transmission module

  2. Check the fluid level and condition by the maker's method.

    Use caution

    Warning:Many transmissions are sealed. Do not open the fill plug without the maker's procedure, because the level depends on temperature.

  3. Inspect the pressure sensor connector and harness for chafing, corrosion and fluid inside the plug.

    Low risk

  4. Have a shop test the pressure sensor signal and circuit against the maker's specification.

    Best left to a shopTool: scan tool and multimeter

    Warning:Shop test. It needs the maker's specifications.

Symptoms

  • Check engine light
  • Lack of power on some Nissans
  • Rough shifts or limp mode Gets more serious: stop and have it checked.

How to fix

  1. Do not clear the code before the transmission module has been read.

  2. Ask a dealer whether your VIN has an open bulletin. Nissan and Ford have published several.

Parts and cost context

  • Transmission control module (TCM):Do not replace the module for P0840 unless tests point to it. Nissan relearns calibration data in the module after a valve assembly repair.

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

Compare used part prices on PartPriceGuide

On your vehicle

Nissan

  • 2007–2008 · Altima

    Supported by vehicle data

    2007-2008 Altima, Rogue and Sentra CVTs: replace the control valve assembly, then erase the calibration data in the TCM and let it relearn. 2007-2008 Altima, Rogue and Sentra with discolored or odd-smelling CVT fluid and the MIL on with P0840 and/or P0845, or with P0710 stored, which may also be stored with P0840 or P0845. Whether the bulletin is still current is not verified.

  • 2007–2008 · Rogue

    Supported by vehicle data

    2007-2008 Altima, Rogue and Sentra CVTs: replace the control valve assembly, then erase the calibration data in the TCM and let it relearn. 2007-2008 Altima, Rogue and Sentra with discolored or odd-smelling CVT fluid and the MIL on with P0840 and/or P0845, or with P0710 stored, which may also be stored with P0840 or P0845. Whether the bulletin is still current is not verified.

  • 2007–2008 · Sentra

    Supported by vehicle data

    2007-2008 Altima, Rogue and Sentra CVTs: replace the control valve assembly, then erase the calibration data in the TCM and let it relearn. 2007-2008 Altima, Rogue and Sentra with discolored or odd-smelling CVT fluid and the MIL on with P0840 and/or P0845, or with P0710 stored, which may also be stored with P0840 or P0845. Whether the bulletin is still current is not verified.

  • 2003–2007 · Murano

    Supported by vehicle data

    Murano (2003-2007 in the flat file): MIL on with P0840 and lack of power. Whether the bulletin is still current is not verified.

  • 2009–2010 · Cube

    Supported by vehicle data

    2009-2010 Cube and Versa: MIL on with one or a combination of these codes; follow the repair flow chart. Whether the bulletin is still current is not verified.

  • 2009–2010 · Versa

    Supported by vehicle data

    2009-2010 Cube and Versa: MIL on with one or a combination of these codes; follow the repair flow chart. Whether the bulletin is still current is not verified.

  • NTB-09-148Status unverified

    Nissan NTB09-148: CVT MIL with P0840, P0845, P0744 and P1777

    2007–2008altima, rogue, sentra · NHTSA 10033269

    2007-2008 Altima, Rogue and Sentra CVTs: replace the control valve assembly, then erase the calibration data in the TCM and let it relearn.

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

  • NTB:09-044Status unverified

    Nissan NTB09-044: discolored or odd-smelling CVT fluid, MIL with P0840/P0845/P0710

    2007–2008altima, rogue, sentra · NHTSA 10030088

    2007-2008 Altima, Rogue and Sentra with discolored or odd-smelling CVT fluid and the MIL on with P0840 and/or P0845, or with P0710 stored, which may also be stored with P0840 or P0845.

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

  • 06084Status unverified

    Nissan 06084: MIL on with P0840, lack of power

    2003–2007murano · NHTSA 10020920

    Murano (2003-2007 in the flat file): MIL on with P0840 and lack of power.

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

  • NTB-10-016Status unverified

    Nissan NTB10-016: MIL with P0740, P0744, P0840 and P1777

    2009–2010cube, versa · NHTSA 10033307

    2009-2010 Cube and Versa: MIL on with one or a combination of these codes; follow the repair flow chart.

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

Ford

  • 2020–2021 · Escape

    Supported by vehicle data

    2020-2021 Escape may lose voltage reference or run rough and blow fuse 44, and may set many codes including P0840, P0842, P0845 and P0847. Whether the bulletin is still current is not verified.

  • SSM 50116Status unverified

    Ford SSM 50116: 2020-2021 Escape loss of voltage reference, many codes including P0840

    2020–2021escape · NHTSA 10201593

    2020-2021 Escape may lose voltage reference or run rough and blow fuse 44, and may set many codes including P0840, P0842, P0845 and P0847.

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

  • P0845Transmission fluid pressure sensor/switch B circuit fault

    Same system Supported by vehicle data

    P0845 is the matching pressure sensor/switch B fault, and Nissan lists both in NTB09-148.

  • P0710Transmission fluid temperature sensor A circuit fault

    Shares causes Supported by vehicle data

    Nissan NTB09-044 lists P0840 and P0845 with P0710 on 2007-2008 CVT cars with odd fluid.

All Transmission codes

P0840 questions

What is transmission fluid pressure sensor A?

It reports hydraulic pressure inside the transmission so the computer can check that shifts are being commanded correctly. P0840 means its circuit reads wrong.

Is P0840 serious?

We found no source that rates it. Have a shop read the transmission module and check the fluid.

Sources and review

  1. P0840 Trouble Code: Transmission fluid pressure sensor/switch A circuit — TroubleCodes.net
  2. Nissan NTB09-148: CVT MIL with P0840, P0845, P0744 and P1777 — Nissan
  3. Nissan NTB09-044: discolored or odd-smelling CVT fluid, MIL with P0840/P0845/P0710 — Nissan
  4. Ford SSM 50116: 2020-2021 Escape loss of voltage reference, many codes including P0840 — Ford
  5. Nissan 06084: MIL on with P0840, lack of power — Nissan
  6. Nissan NTB10-016: MIL with P0740, P0744, P0840 and P1777 — Nissan
Last reviewed
Written by
Saurabh K.
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