P0512
PowertrainStarter Request Circuit
The starter request circuit is the wiring and signalling path that tells the starter motor to engage when you turn the key or press the button. The ECM keeps an eye on this circuit, and when it sees a voltage or signal that doesn't add up, it logs P0512. The usual result is hard starting, slow cranking, or sometimes no crank at all, and on cars with an immobiliser it can be that system blocking the start request rather than the starter itself.
ⓘ Information only. This page provides general educational information about fault code P0512. We do not assess the urgency or safety implications of any specific fault. That requires in-person diagnosis by a qualified mechanic. Full terms.
Recommended next steps
Whether a fault is urgent, drivable, or routine depends entirely on the cause on a specific vehicle, and that can only be determined by a qualified mechanic with diagnostic equipment. If a warning light is illuminated, the most reliable next step is professional diagnosis.
What does P0512 mean?
P0512 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Starter Request Circuit.
This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms commonly associated with this code
Symptoms that drivers often report alongside this code. Not all may apply to every case:
- • Engine won't fire, or you're turning the key two or three times before it catches
- • Long cranking before it finally starts
- • Cranks over fine but just won't start
- • Check Engine Light on the dash
- • A pause between turning the key and the starter actually pulling in
- • Rarely, the engine cutting out while you're driving
Possible causes
Causes commonly associated with P0512, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. Weak or poorly connected battery, this is where the most P0512s come from because starting pulls the heaviest current in the whole car and a tired battery sags below what the circuit needs
- 2. Corroded or loose wiring and connectors in the starter request circuit, classic on older cars where road salt has had years to get at the terminals
- 3. Failing ignition switch, the contacts inside wear and stop passing a clean signal
- 4. Starter relay gone bad, or pitted relay contacts not closing properly
- 5. Immobiliser or key transponder playing up, including a flat key fob battery, which stops the ECM authorising the start
- 6. Blown fuse or fusible link feeding the starter or ignition side
- 7. ECM fault or a software glitch, the least likely cause and the last one to chase
How mechanics typically diagnose
A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training.
- 1. Load test the battery and check the terminals before anything else. A reading of at least 12.5 to 12.6 volts at rest is what you want, and clean tight connections matter as much as the voltage figure
- 2. Scan for stored codes and note anything immobiliser or ignition related sitting alongside the P0512, because that often points you straight at the cause
- 3. Pull and check the relevant fuses and fusible links for the starter and ignition circuits
- 4. Go over the wiring, connectors and terminals in the starter request circuit looking for green corrosion, chafing, or a plug that's worked loose
- 5. Swap the starter relay with a matching one from another circuit, or test it for continuity and voltage against the wiring diagram
- 6. Confirm the ignition switch is doing its job and, on cars with an immobiliser, check the antenna ring around the barrel and the key fob battery
Common questions about P0512
What happens if I just keep driving with P0512 showing? +
If it starts and runs as normal you can carry on, but understand the fault is electrical and tends to get worse, not better. The risk is being left stranded one cold morning when the battery is at its weakest and the circuit finally gives up. If it's already taking several attempts to start, or the engine has cut out on you while driving, stop using the car until it's sorted. A no-start in traffic or a stall on the motorway is not a risk worth taking.
How quickly do I need to deal with this? +
Treat it as soon rather than later, especially heading into winter. A weak battery or corroded connection that throws this code in mild weather can leave you with a dead car when temperatures drop. If the car still fires up reliably you've got a bit of breathing room to book it in, but don't ignore it for weeks. The cheap causes like a tired battery or dirty terminals are easy and quick to fix; leave it and you risk it turning into a roadside callout.
Is it the starter circuit parts that have failed or just the wiring and connections? +
On this code it's very often the connections rather than an expensive component. Battery terminals, the relay contacts, and corroded plugs in the circuit cause a big share of these, and all of those are cheap to put right. The ignition switch and immobiliser are real possibilities but further down the list. Check the easy, low-cost electrical stuff thoroughly before anyone talks you into a new starter motor or an ECM, because the wiring and battery are where the money usually isn't.
Information only, not professional advice
The information on this page is provided for general guidance and educational purposes only. It is not a substitute for diagnosis or repair advice from a qualified mechanic. Always verify any fault before paying for repairs. carfaultcodes.co.uk accepts no liability for decisions made based on this information. Full terms →