Starter Request Circuit

What P0512 means

On a modern vehicle the starter is not wired straight to the key. When you turn the ignition to START — or, on push-button-start vehicles, press the button after the immobilizer authorizes it — a start request is sent to a control module (the PCM, and on many vehicles the body control module first). That module checks the enabling conditions (transmission in Park or Neutral, brake or clutch applied, valid anti-theft key) and only then energizes the starter relay, which in turn feeds the starter solenoid. P0512 sets when the module sees the incoming start-request signal as electrically faulty or implausible: the line is open, shorted, or reports a state that does not agree with what the module expects. On the 2014 Ford F-150 the DTC chart labels this exactly 'Starter Request Circuit' and directs the technician to the Starting System / PCM diagnostics to continue. The same fault family appears on Chrysler and Jeep push-button and keyed-immobilizer systems. Because the fault is on the request side of the circuit, the symptom is a cranking problem — intermittent no-crank, no-crank, or the driver having to press the start button several times — rather than a slow, dragging crank.

Symptoms

• Engine cranks intermittently or not at all when you turn the key to start or press the start button
• You have to try the key or push the start button multiple times before the starter engages
• Check-engine light on, with P0512 stored (sometimes as a continuous-memory fault that only appears after a failed start)
• No-crank with a fully charged battery and a starter that bench-tests good — the request never reaches the relay
• Occasional dash message such as 'Push brake to start' or a start that only works in one gear-selector position
• Starter relay never clicks even though the battery, ground, and starter cables are all healthy

Common causes

• Worn or faulty ignition/start switch that sends an intermittent or dropped START-request signal
• On push-button systems, a failing start/stop button or its low-signal wiring to the body control module
• Open, shorted, or chafed wiring in the start-request circuit between the switch/button, the body module, and the PCM
• Corroded, loose, or backed-out connector pins at the ignition switch, BCM, or PCM carrying the request signal
• Faulty or high-resistance starter relay control circuit that makes the request read implausible to the module
• Body control module fault that fails to pass a valid start request through to the PCM
• PCM internal fault on the starter-request input (uncommon — confirm the switch, wiring, and modules first)
• Anti-theft/immobilizer or park-neutral (PNP/clutch) input problem that leaves the module unable to validate the request

Severity & driving advice

Severity: Moderate — The vehicle runs and drives normally once started, but an intermittent starter-request fault can leave you stranded with a no-crank.

Can I drive? Once running it drives normally — P0512 doesn't affect how the vehicle runs. The risk is restarting: the fault is intermittent, so you may be unable to crank and get stranded. Diagnose it soon, especially before long trips.

Diagnostic approach

1. Scan and read freeze-frame — Confirm P0512 and record any companion codes — especially body-module, immobilizer/PATS, or park-neutral (PNP/clutch switch) faults, since P0512 depends on those enabling inputs. Note whether the code is stored in continuous memory (it sets during a real start attempt) and whether it is intermittent.
2. Verify the basics first — Rule out the things that mimic a no-crank: load-test the battery, confirm clean tight battery and engine grounds, and check the starter feed. P0512 is a request-circuit fault, so the battery and starter motor should test good — if the crank is slow or dragging, that points elsewhere, not at this code.
3. Confirm the enabling conditions — The module only forwards a start request when Park/Neutral (or clutch), brake, and the immobilizer all agree. Watch the PNP/gear-selector, brake-switch, and anti-theft PIDs on the scan tool while attempting a start to confirm each enabling input reads correctly and none of them is blocking the request.
4. Inspect the start-request wiring and connectors — Examine the harness and connectors from the ignition switch (or start button) to the body control module and PCM for chafed insulation, backed-out or corroded pins, and moisture. On the Ford application, work the Ignition Switch and Starting System connector end-views; a wiggle test while attempting a start often catches an intermittent open.
5. Test the request signal at the switch/button — Back-probe the start-request line and watch it change state as you cycle the key to START or press the button. A healthy circuit should swing cleanly between its rest and active levels; a signal that stays flat, is noisy, or only sometimes appears identifies an open switch, a bad button, or a broken wire on the request side.
6. Check the circuit through the modules — Trace continuity of the request circuit between the switch/BCM and the PCM with the connectors open, checking for opens and for shorts to power or ground. Confirm the body module is actually passing the request through — a valid request in but nothing forwarded to the PCM points at the BCM rather than the wiring.
7. Follow the factory Starting System / PCM routine, then verify — The 2014 F-150 chart routes P0512 to the Starting System, PCM DTC diagnostics — complete that pinpoint path before condemning any module. After the repair, clear the code and perform several real start cycles (including cold and after sitting) to confirm the engine cranks reliably and P0512 does not return to continuous memory.

FAQ