P0638 The electronic throttle is not reaching the position the engine computer asked for, so the throttle actuator control on bank 1 is out of its expected range

Throttle actuator control range/performance, bank 1

P0638 in short

P0638 means the electronic throttle body isn't moving to the position the engine computer commands. A dirty or failing throttle body, a worn position sensor, wiring faults, ice in the throttle after a cold night, or software are typical causes. Expect reduced power; have it diagnosed soon and stop if power drops sharply.

On a drive-by-wire engine, the computer reads the accelerator pedal and drives a small motor that opens the throttle plate. Two position sensors report back where the plate actually is.

P0638 sets when the actual position differs from the requested position for too long. Saab's service information, for example, sets it after more than a second of deviation with normal battery voltage. A sticking, dirty or damaged throttle, a weak motor or a bad connection are the usual reasons.

Bulletins show a pattern: Hyundai and Kia fixed it with throttle sensor replacement, throttle cleaning and ECM software, while Mazda and Saturn traced cold-weather cases to moisture freezing in the throttle.

Most likely causes

  1. Dirty, sticking or failing throttle body

    Common general cause
    Why it ranks here
    KBB names a faulty or dirty throttle body as the most common cause, and Saab checks for a binding or damaged throttle.
    What would change this
    Likelier if the plate is coated in carbon or doesn't move smoothly with the engine off.
    How to test the electronic throttle body

  2. Throttle position sensor or ECM software (bulletin fix)

    Supported by vehicle data
    Why it ranks here
    Hyundai and Kia bulletins fix P0638 with a sensor replacement, throttle cleaning and ECM updates.
    What would change this
    Likelier on a Hyundai or Kia V6 covered by a bulletin.
    How to test the engine control module (ecm / pcm)

  3. Moisture freezing the throttle after cold parking

    Supported by vehicle data
    Why it ranks here
    Mazda and Saturn bulletins link P0638 to cold starts below freezing, with condensation freezing the throttle.
    What would change this
    Likelier if the code only appears on the first start after a freezing night.
    How to test the electronic throttle body

  4. Throttle wiring or connector fault

    Common general cause
    Why it ranks here
    Saab lists wiring and connectors first, and KBB lists damaged wiring.
    What would change this
    Likelier if the fault comes and goes over bumps or the connector shows corrosion or pushed-back pins.

  5. Engine computer fault

    Possible — needs testing
    Why it ranks here
    KBB calls a PCM failure rare; rule out everything else first.
    What would change this
    Only likely after the throttle, wiring and software are ruled out.
    How to test the engine control module (ecm / pcm)

What to test first

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

  1. Read all codes, note whether they set after a cold start, and check for bulletins covering your vehicle

    Low riskTool: OBD-II scan tool

  2. With the ignition off and the key out, remove the intake duct and inspect the throttle plate for carbon and binding; check the throttle connector

    Use cautionTool: Flashlight

    Warning:The throttle motor can snap the plate shut with force. Never put fingers in the throttle bore unless the ignition is off and the key is away from the car.

  3. Watch both throttle position sensors while commanding the throttle with a bidirectional scan tool and wiggling the harness

    Best left to a shopTool: Bidirectional scan tool

    Warning:Commanding the throttle moves the plate with force; keep hands and tools clear of the throttle bore.

Symptoms

  • Check engine light, sometimes with an electronic throttle or wrench light
  • Reduced power or limp mode
  • Rough idle or rpm fluctuating when cold
  • Sudden loss of power or stalling while driving Gets more serious: stop and have it checked.

Compare with: Check engine light with loss of power

How to fix

  1. Ask a dealer to check your VIN for throttle or ECM software bulletins; Hyundai, Kia and Mazda have published fixes for P0638.

  2. If the code returns, have the throttle body inspected and cleaned or replaced, followed by the throttle relearn.

Parts and cost context

  • Electronic throttle body:Cleaning sometimes fixes it; replacement needs a throttle relearn afterwards. 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

Hyundai

  • 2006–2009 · Azera

    Supported by vehicle data

    Throttle position sensor replacement and ECM update for P0638 or P2135 on V6 models. Whether the bulletin is still current is not verified.

  • 2006–2010 · Santa Fe

    Supported by vehicle data

    Revised throttle sensor and ECM fix for P0638/P2135 on 2.7/3.3/3.8L engines. Whether the bulletin is still current is not verified.

  • 2010–2012 · Santa Fe

    Supported by vehicle data

    ECM software for P0638 on the 3.5L. Whether the bulletin is still current is not verified.

  • TSB-09-FL-003Status unverified

    MIL with P2135 or P0638: TPS replacement and ECM update

    2006–2009azera, sonata, santa-fe, veracruz, entourage · issued · NHTSA 10029229

    Some vehicles show a MIL with electronic throttle control codes P2135 or P0638, or a slight rpm fluctuation at cold warm-up; fixed by replacing the throttle position sensor and updating the ECM.

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

  • TSB-10-FL-010Status unverified

    P2135/P0638 or cold rpm fluctuation: TPS replacement and ECM update

    2006–2010santa-fe, sonata, azera, veracruz · issued · NHTSA 10034649

    Revised version of the TPS replacement and ECM update for P2135/P0638 on 2.7/3.3/3.8L engines, adding the 2009-2010 Genesis.

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

  • 14-01-054Status unverified

    ECM software for P0638/P2106/P2110 (3.5L)

    2010–2012santa-fe · NHTSA 10057210

    ECM software update for 3.5L Santa Fe with P0638, P2106 or P2110.

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

Kia

  • 2011–2014 · Sorento

    Supported by vehicle data

    ECM upgrade and throttle cleaning for P0638 on the 3.5L Sorento and Sedona. Whether the bulletin is still current is not verified.

  • TSB-ENG133R2Status unverified

    ECM upgrade for P0638 and throttle motor cleaning (3.5L)

    2011–2014sorento, sedona · issued · NHTSA 10109712

    ECM software upgrade and electronic throttle cleaning for 2011-2013 Sorento and 2011, 2012 and 2014 Sedona 3.5L MPI that may show a MIL with P0638.

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

Mazda

  • 2016–2018 · CX-9

    Supported by vehicle data

    Throttle can freeze after parking below freezing, causing lack of power with P0638. Whether the bulletin is still current is not verified.

  • 2016–2018 · CX-9

    Supported by vehicle data

    Earlier version of the frozen-throttle bulletin. Whether the bulletin is still current is not verified.

  • 01-001-20Status unverified

    Lack of power after parking below freezing, P0638/P2112

    2016–2018cx-9 · issued · NHTSA 10170634

    Condensation from the intake manifold can freeze the throttle valve in its standby position after parking below freezing, giving a lack of power with P0638 and/or P2112.

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

  • 01-001-18Status unverified

    Lack of power after parking below freezing, P0638/P2112

    2016–2018cx-9 · issued · NHTSA 10129572

    Earlier version of the frozen-throttle bulletin: lack of power with P0638/P2112 after parking in freezing weather.

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

Saturn

  • 2000–2005 · L200

    Supported by vehicle data

    Reduced power lamp with P0638 after cold starts below freezing. Whether the bulletin is still current is not verified.

  • 04-06-04-085Status unverified

    Reduced power lamp after cold start below freezing, P0638

    2000–2005l200, l300, ls · issued · NHTSA 10011533

    Service engine soon and/or reduced power lamp after a cold start in subfreezing temperatures, with P0638, P1510 and/or P1516 stored.

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

  • P2135Two throttle or pedal position sensor signals (A and B) that should agree with each other don't

    Shares causes Supported by vehicle data

    Hyundai's throttle bulletins cover P2135 and P0638 with the same sensor and software fix.

  • P2112The engine computer commanded the electronic throttle to open but saw it stay more closed than expected

    Shares causes Supported by vehicle data

    Mazda's frozen-throttle bulletin lists P2112 with P0638.

  • P2110The engine computer has deliberately limited engine speed because of a fault it found in the electronic throttle system

    Primary / secondary Supported by vehicle data

    Likely primary: P0638. P2110 is the forced-limited-rpm fail-safe; Hyundai's Santa Fe software bulletin covers it with P0638.

  • P2106The engine computer has limited engine power as a fail-safe because of a throttle control fault

    Primary / secondary Supported by vehicle data

    Likely primary: P0638. P2106 means throttle forced limited power; it appears with P0638 in Hyundai's Santa Fe bulletin.

All Electronic throttle and accelerator pedal codes

Sources and review

  1. P0638 Throttle Actuator Control Range/Performance Bank 1 — Kelley Blue Book
  2. Saab 9-3 (2008) ME9 DTC P0638 Throttle Position Deviation from Demanded — Saab Automobile (WIS)
  3. Electronic Throttle Control (Throttle-By-Wire) — AA1Car (Larry Carley)
  4. NHTSA recall 26V081: Electronic throttle body gears may break (2024-2025 Nissan Rogue 1.5L VC-Turbo) — Nissan North America / NHTSA ,
  5. Hyundai TSB-09-FL-003: MIL with P2135 or P0638, or cold rpm fluctuation - TPS replacement and ECM update — Hyundai Motor America / NHTSA ,
  6. TSB-10-FL-010: P2135/P0638 or cold rpm fluctuation: TPS replacement and ECM update — Hyundai Motor America / NHTSA ,
  7. Kia TSB-ENG133R2 (SA153): ECM upgrade for MIL with P0638 and ETC motor cleaning (Sorento, Sedona 3.5L) — Kia America / NHTSA ,
  8. Hyundai 14-01-054: ECM software for P0638/P2106/P2110 (Santa Fe 3.5L) — Hyundai ,
  9. Mazda 01-001-20: lack of power after parking in freezing weather, P0638/P2112 (CX-9) — Mazda North American Operations / NHTSA ,
  10. 01-001-18: Lack of power after parking in freezing weather, P0638/P2112 (CX-9) — Mazda North American Operations / NHTSA ,
  11. Saturn 04-06-04-085: SES or reduced power lamp after cold start in subfreezing temperatures, P0638 (L-Series) — General Motors / NHTSA ,
  12. P0222 Throttle/Pedal Position Sensor/Switch B Circuit Low — Kelley Blue Book
Last reviewed
Written by
Saurabh K.
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