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Technical Description of OBD-II Trouble Code
Issue with Starter Request Circuit
What does that signify?
This diagnostic trouble code (DTC) is a generic powertrain code that is applicable to all vehicles manufactured from 1996 onwards (Dodge, Chrysler, Hyundai, Jeep, Mazda, etc.). While it is a generic code, the specific repair steps may vary depending on the make and model of the vehicle.
Whenever I come across a stored code P0512, it indicates that the powertrain control module (PCM) has detected a malfunction in the starter request circuit. In this case, the term “starter” refers to the engine starter.
Although the starter receives constant battery voltage from the positive cable, the starter request signal originates from the ignition switch. When the ignition key is inserted into the ignition cylinder and turned to the start position, it activates the electrical part of the ignition switch and closes a set of heavy-duty contacts, completing the starter request circuit. Once the starter request circuit is complete, a battery voltage signal is sent to the starter solenoid (or the starter relay in some models). In the vehicle being diagnosed, it means that a starter request signal should also be sent to the PCM. Since a code P0512 has been stored, it is likely that the PCM has not received the starter request signal.
Once the starter request signal is received by the starter solenoid, the starter motor starts spinning and a small cog is pushed towards the engine, where the teeth of the cog engage with the teeth of the flywheel ring gear. This action turns the engine crankshaft and helps initiate startup.
Refer to a reliable source of vehicle information (such as All Data DIY) to determine if the vehicle in question is equipped with a starter relay. If it is, you will need to locate the relay and the system wiring diagram. Typically, the ignition switch provides the starter relay with a starter request signal. After receiving the signal, the relay then provides the starter and the PCM with a starter request signal. After that, the starter and solenoid function in the same way as a vehicle without a starter relay.
Even if there are no noticeable symptoms, if the PCM fails to receive the starter request signal and the engine is started, a code P0512 will be stored and a malfunction indicator lamp may illuminate. Some vehicles require multiple ignition cycles (with a failure) for the MIL to illuminate.
Severity & Symptoms
If the engine cranks normally, a P0512 code can be addressed at your convenience. However, if the engine fails to start, the code will need to be addressed with a certain level of urgency.
Symptoms of a P0512 code may include:
Causes
Possible causes for this code include:
Diagnostic and Repair Procedures
A good starting point is always to check for technical service bulletins (TSB) for your particular vehicle. Your issue may be a known problem with a known solution provided by the manufacturer, which can save you time and money during diagnosis.
When diagnosing a P0512, you will need a diagnostic scanner, a digital volt/ohmmeter (DVOM), and a vehicle information source (such as 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 being engaged, as fuses on unloaded circuits may appear operational until the circuit is loaded.
You must now determine whether or not the vehicle in question is equipped with a starter relay. If it is, a simple and easy test is to swap the starter relay with a known good relay. Since most manufacturers use identical relays for multiple functions, you may swap one relay for another for diagnostic purposes. If the problem is resolved after swapping the relays, swap them back and replace the starter relay with a new one.
To test the relay without swapping relays, refer to your vehicle information source and find the starter system wiring diagram. The starter relay connector view will also be helpful. Test for a battery voltage input circuit to the starter relay. This circuit should maintain battery voltage when the ignition switch is in the on position (referred to as switched voltage). If there is no voltage being input to the starter relay, check system fuses, fusible links, and wiring from the battery or battery junction box. In most cases, the ignition switch will provide the relay with a secondary voltage source signal when the ignition switch is turned to the start position. At the same time, the PCM will provide a ground signal to the starter relay. The secondary voltage and ground signals will cause contacts inside the relay to close, completing the starter request circuit, which should send a signal to the starter solenoid and back to the PCM.
Before testing circuit resistance with the DVOM, disconnect all related controllers. Test the voltage signal to the relay (from the ignition switch) first. If it is not present, suspect a defective ignition switch or wiring malfunction. If the secondary voltage input is present, check the ground signal input from the PCM. If there is no ground being input to the starter relay from the PCM, suspect PCM failure or a PCM programming error.
There could also be a wiring malfunction between the PCM and the starter relay.
Additional diagnostic notes:
Professional Service
While we always recommend resolving this issue mechanically, if for some reason that is not possible, we offer the option to permanently delete this specific DTC. All other codes will continue to function. If you are interested in this option, please upload your ECU file to our portal.
