What does it mean?
This diagnostic trouble code (DTC) is a generic powertrain code, meaning it applies to all vehicles made after 1996 (Dodge, Chrysler, Hyundai, Jeep, Mazda, etc.). Although generic, specific repair steps may vary by make/model.
Whenever I encounter a stored P0512 code, it means the Powertrain Control Module (PCM) has detected a malfunction in the starter request circuit. In this context, “starter” refers to the engine starter.
While the starter receives constant battery voltage through the positive cable, the starter request signal comes from the ignition switch. When the ignition key is inserted into the cylinder and turned to the start position, it activates the electrical portion of the ignition switch and closes a set of heavy-duty contacts, completing the starter request circuit. When the starter request circuit is completed, a battery voltage signal is sent to the starter solenoid (or starter relay on some models). In the vehicle you’re diagnosing, this means a starter request signal must also be sent to the PCM. Since a P0512 code has been stored, the PCM likely didn’t receive the starter request signal.
Once the starter request signal is received by the starter solenoid, the starter begins to spin and a small pinion gear is pushed toward the engine where the pinion teeth engage with the teeth of the flywheel ring gear. This rotates the engine’s crankshaft and helps initiate starting.
Consult a reliable vehicle information source (All Data DIY is excellent) to determine if the vehicle in question has a starter relay. If so, you’ll need to locate the relay and the system wiring diagram. Typically, the ignition switch provides the starter relay with a starter request signal. Once the relay receives this signal, it then provides both the starter and PCM with a starter request signal. After this, the starter and solenoid operate exactly the same as in vehicles without a starter relay.
Even if there are no symptoms, if the PCM doesn’t receive the starter request signal and the engine starts, a P0512 code will be stored and a malfunction indicator light may illuminate. Some vehicles require multiple ignition cycles (with a fault) for the MIL to illuminate.
Severity and Symptoms
If the engine starts normally, a P0512 can be addressed at your convenience. Obviously, if the engine won’t start, the code needs to be treated with some urgency.
Symptoms of a P0512 code may include:
Engine may not start
Delayed starter engagement (starting may require multiple key cycles)
PCM power circuit failure codes or ignition system circuit failure codes may accompany this code
Often there are no symptoms
Causes
Possible causes of this code include:
Faulty ignition switch
Blown fuses or burned fusible links
Defective starter relay
Open or shorted circuits in the starter request circuit
PCM error or PCM programming error
Diagnostic and Repair Procedures
A good starting point is always checking technical service bulletins (TSBs) for your specific vehicle. Your problem might be a known issue with a published manufacturer fix that could save you time and money during diagnosis.
When diagnosing a P0512, you’ll need a diagnostic scanner, digital volt/ohmmeter (DVOM), and a vehicle information source (like All Data DIY).
Begin with a visual inspection of all related wiring and connectors. This is also a good time to check all fuses using the DVOM. Check starter system fuses while the starter is engaged, since fuses in unloaded circuits may appear operational until the circuit is loaded.
Now determine whether the vehicle in question has a starter relay. If it does, a simple and easy test is to replace the starter relay with a known good relay. Since most manufacturers use identical relays for multiple functions, you can swap one relay for another for diagnostic purposes. If the problem is resolved after swapping relays, swap them back and replace the starter relay with a new one.
To test the relay without swapping, consult your vehicle information source and find the starter system wiring diagram. The starter relay connector view will also prove useful. Test for battery voltage input circuit to the starter relay. This circuit should maintain battery voltage when the ignition switch is in the run position (this is called switched voltage). If no voltage is entering the starter relay, check system fuses, fusible links, and wiring from the battery or battery junction box. In most cases, the ignition switch provides the relay with a secondary voltage source signal when the ignition switch is turned to the start position. Simultaneously, the PCM will provide a ground signal to the starter relay. The secondary voltage and ground signals will cause the contacts inside the relay to close, completing the starter request circuit that should send a signal to the starter solenoid and back to the PCM.
Disconnect all related controllers before testing circuit resistance with the DVOM. First test the voltage signal to the relay (from the ignition switch). If it’s not present, suspect a faulty ignition switch or wiring malfunction. If the secondary voltage input is present, check the ground signal input from the PCM. If there’s no ground from the starter relay to the PCM, suspect PCM failure or PCM programming error.
There could also be a wiring malfunction between the PCM and starter relay.
Additional Diagnostic Notes:
This code will rarely appear in vehicles without a starter relay (I’ve never seen it)
To avoid misdiagnosis, once repairs are completed and the code is cleared, operate the vehicle normally until the PCM enters readiness mode or the code resets
Before swapping relays (for diagnostic purposes), ensure they have matching service numbers
Always return relays to their original positions and replace faulty relays with new ones