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P0639Throttle Actuator Control Range/Performance (Bank 2)

The electronic throttle actuator on Bank 2 is not moving its throttle plate to the position the PCM is commanding.

Definition

Some V-configuration and high-performance engines use a separate throttle body per bank, and the PCM verifies each actuator's actual plate angle against the commanded angle through its throttle position sensors. P0639 sets when the Bank 2 throttle's actual position deviates from the commanded position beyond tolerance, indicating binding, a slow motor, or bad position feedback on that throttle body. The PCM typically forces reduced engine power or limits throttle authority, the MIL and ETC warning illuminate, and the engine may run unevenly because the two banks are no longer breathing equally. Symptoms mirror P0638 but isolate the fault to the Bank 2 throttle assembly and its circuits.

Common causes

  • Carbon or oil residue binding the Bank 2 throttle plate
  • Worn actuator motor or damaged gears inside the Bank 2 throttle body
  • Wiring or connector damage in the Bank 2 throttle motor or TPS circuits
  • Faulty throttle position sensor feedback on the Bank 2 unit
  • Low charging system voltage reducing actuator torque
  • PCM driver fault on the Bank 2 throttle control channel

Common misdiagnoses

  • Replacing the Bank 1 throttle body instead of correctly identifying Bank 2
  • Replacing the accelerator pedal sensor, which affects both banks and sets different codes
  • Replacing both throttle bodies when only the Bank 2 harness was damaged
  • Replacing the PCM before checking the actuator circuits and supply voltage

Troubleshooting steps

  1. 1.Identify Bank 2 and compare commanded versus actual position

    Confirm which throttle body serves the bank opposite cylinder 1, then watch its desired and actual angle PIDs for lag or deviation during a throttle sweep.

  2. 2.Inspect and clean the Bank 2 throttle body

    Check the plate and bore for carbon buildup or oil from the PCV system and clean per the service procedure, avoiding forcing the plate on geared actuators.

  3. 3.Test the Bank 2 actuator wiring

    Verify motor circuit continuity under 1 ohm end to end, no shorts to ground or voltage, and clean, tight connector terminals at the throttle body.

  4. 4.Verify system voltage

    Confirm 13.5-15.0 volts running, since a weak charging system degrades both actuators but often sets a code on the higher-resistance circuit first.

  5. 5.Relearn and verify

    Perform the throttle relearn, then confirm both banks' actual angles track commanded within a few percent through idle and wide-open throttle.

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