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P codepowertrainMedium severity

P0512Starter Request Circuit

The engine computer sees an implausible or faulty signal on the starter request circuit.

Definition

On vehicles where the PCM controls or monitors starter engagement, the starter request line from the ignition switch (or body/immobilizer module) tells the PCM the driver is commanding a crank. P0512 sets when that signal is present at the wrong time — for example, a start request while the engine is already running — or when the circuit shows an open or short. Symptoms range from a stored code with no complaint to a no-crank condition or a starter that engages erratically.

Common causes

  • Worn or faulty ignition switch contacts
  • Chafed wiring shorting the starter request circuit to power or ground
  • Faulty starter relay or relay control circuit
  • Improperly installed remote starter or aftermarket alarm tapping the crank circuit
  • Sticking push-button start switch or clutch/park-neutral input fault
  • PCM input circuit fault (rare)

Common misdiagnoses

  • Starter motor replacement
  • Battery replacement
  • Neutral safety switch replaced without testing the request circuit
  • PCM

Troubleshooting steps

  1. 1.Check when the code sets

    Note whether the code returns immediately, only during cranking, or after the engine starts; a request signal that stays high after start points to the ignition switch or a short to power.

  2. 2.Monitor the starter request PID

    Watch the starter request status on a scan tool through a full key cycle; it should show active only while the key is in START.

  3. 3.Inspect for aftermarket wiring

    Look under the column and at the ignition harness for remote-start or alarm taps, which commonly backfeed the crank request line.

  4. 4.Test the ignition switch output

    Verify battery voltage on the request circuit only in the START position and 0 V in RUN; voltage present in RUN indicates worn switch contacts or a short.

  5. 5.Check the circuit end-to-end

    With the switch disconnected, confirm the wire to the PCM has no short to voltage or ground and less than 1 ohm of resistance, then repair or replace the faulty component.

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