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P codepowertrainMedium severity

P0659Actuator Supply Voltage "A" Circuit High

The actuator supply voltage "A" circuit is reading high when it should be off or regulated, typically from a short to battery voltage or a stuck-on driver.

Definition

The PCM expects its switched actuator supply "A" to be at battery voltage only when commanded on and near zero when off; P0659 sets when the monitored voltage is high at the wrong time or above the expected range. The usual causes are the supply wire shorted to an always-hot circuit or a PCM high-side driver stuck on, which can keep actuators powered after key-off and slowly drain the battery. The MIL illuminates and the PCM may disable the affected actuators, producing reduced engine power or default transmission shifting.

Common causes

  • Supply wire chafed into a battery-voltage circuit in the harness
  • PCM high-side driver stuck on internally
  • Melted connector or harness section bridging the supply to a hot feed
  • Aftermarket wiring spliced into the actuator supply circuit
  • Water intrusion in a junction connector bridging adjacent power terminals

Common misdiagnoses

  • Actuators or solenoids replaced when the supply feed itself is compromised
  • Battery replaced for the parasitic drain caused by a stuck-on supply
  • Alternator replaced for a suspected overvoltage condition
  • Ignition switch replaced without tracing the actual backfeed

Troubleshooting steps

  1. 1.Verify the condition key-off

    Measure the actuator supply circuit with the key off; battery voltage present confirms a short to a hot feed or a stuck PCM driver.

  2. 2.Disconnect the PCM and re-measure

    If voltage on the circuit disappears with the PCM unplugged, the internal driver is stuck on; if voltage remains, the harness is shorted to power.

  3. 3.Trace the harness for the power short

    Inspect routing shared with battery and ignition feeds — junction blocks, splice packs, and areas of heat damage — for the bridge point.

  4. 4.Check for parasitic drain

    Perform a parasitic draw test (target below about 50 mA after modules sleep); a stuck-on actuator supply typically shows a persistent draw worth confirming after the repair.

  5. 5.Repair and verify switching

    After the fix, confirm the supply toggles correctly between 0 volts key-off and battery voltage when commanded, then clear codes and re-test.

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