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DTC codes / P05xx · Vehicle speed, idle control and auxiliary inputs / P0512

P0512Starter Request Circuit

P0512 indicates that the powertrain control module (PCM) has detected an abnormal condition in the starter request circuit, which is the electrical path that carries the signal from the ignition switch to the PCM when you turn the key to the start position. The PCM expects a specific voltage or signal on this circuit during cranking, and when that signal is missing, erratic, or present at the wrong time, it stores this code and may illuminate the check engine light.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaVehicle speed, idle control and auxiliary inputs

Symptoms you may notice

  • The engine may not crank at all when you turn the key to start, or it may crank intermittently.
  • The check engine light is illuminated, often with no other noticeable driveability symptoms.
  • The starter may engage but the engine fails to start, or the starter may run unexpectedly.
  • In some cases, the vehicle may start normally but the warning light remains on.
  • A no-crank condition that is worse in cold or damp weather, or after the vehicle sits.
  • The security or immobilizer system may act up, preventing cranking even with the key in the start position.

Common causes, most likely first

  1. Faulty ignition switch or starter switch contacts that fail to send a clean start signal.
  2. Damaged or corroded wiring in the starter request circuit, including open circuits, shorts to ground, or high resistance connections.
  3. Poor ground connection at the PCM, starter, or engine block, causing voltage drops that confuse the PCM.
  4. Failed or sticking starter relay, preventing the request signal from reaching the PCM or starter.
  5. Defective neutral safety switch (automatic transmission) or clutch pedal position switch (manual transmission) that interrupts the start request.
  6. PCM internal fault or corrupted software, though this is less common and should be diagnosed last.
  7. Aftermarket alarm or remote start system improperly wired into the starter request circuit, causing signal interference.

How to diagnose and fix it

  1. Verify the battery is fully charged and load-test it, as a weak battery can cause erratic start signals and set this code.
  2. Inspect and test the ignition switch and starter switch for proper continuity and voltage output in the start position.
  3. Check all fuses and relays related to the starter circuit, including the starter relay and any underhood or interior fuse box connections.
  4. Perform a voltage drop test on the starter request circuit wiring from the ignition switch to the PCM, looking for excessive resistance or open circuits.
  5. Test the neutral safety switch or clutch pedal position switch for proper operation and adjustment.
  6. Inspect and clean all ground connections at the PCM, starter, and engine block, then retest the circuit.
  7. If all circuits test good, consult the factory service information for specific PCM pinout tests and consider reprogramming or replacing the PCM only after confirming no other faults exist.

Starter request circuit pitfalls to avoid

  • A common misdiagnosis is replacing the starter motor when the actual fault is a faulty ignition switch or a corroded connection in the starter request circuit, so always test the control side before condemning the starter.
  • The PCM may set P0512 even when the engine starts and runs normally, because the code can be triggered by a brief glitch in the start signal that does not prevent cranking, so do not assume a no-crank condition is present.
  • Aftermarket remote start or alarm systems are frequently tapped into the starter request wire, and a poor splice or module failure can set this code without any obvious wiring damage.
  • A weak or failing battery can cause voltage spikes or drops during cranking that the PCM interprets as an invalid starter request signal, so always load-test the battery before diving into circuit diagnostics.
  • On some vehicles, the starter request signal passes through the body control module (BCM) or a smart junction box, so a fault in those modules can set P0512 even though the PCM itself is fine.

Can I keep driving with P0512?

If the engine cranks and starts normally, you can drive the vehicle to a repair shop, but avoid turning the key off and on repeatedly until the fault is fixed. If the engine does not crank or cranks intermittently, do not continue driving because you may be stranded; have the vehicle towed or repaired on-site.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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