P0512 – Starter request circuit -malfunction

By Benjamin Jerew (Contact Me)
Last Updated 2016-03-21
ASE Master Tech

Trouble CodeFault LocationProbable Cause
P0512 Starter request circuit -malfunction Wiring, immobilizer system, relay

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What Does Code P0512 Mean?

We’ve certainly come a long way since starting our cars with a hand-crank, moving through push-button ignition and all manner of keyed ignitions. In the interest of security, it was found that even intricate and hard-to-duplicate mechanical keys weren’t enough to prevent unwanted engine starting, leading to the development of the engine immobilizer system. Then, mechanical keys were paired with specialized resistors and uniquely-coded radio transponders, even in in modern push-button ignition systems.

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Just as keys need to be cut or “programmed” to match the vehicle ignition cylinder, the engine immobilizer system needs to be programmed to recognize the transponder. Basically, the immobilizer uses a small antenna to detect the appropriate transponder signal when engine start is requested, either by turning the physical key to the start position or when the driver steps on the brake and presses the start-stop button. If the engine immobilizer system recognizes the transponder, it enables the fuel and ignition system and the starter. If not, it locks out the starter or the engine control module (ECM), making the vehicle impossible to drive.

In some cases, the engine immobilizer system, which may or may not be part of the ECM, may have a hard time recognizing the transponder, even if it is properly registered. In this case, the engine immobilizer system, may lock out the ECM or starter, set a diagnostic trouble code (DTC), P0512 “Starter Request Circuit,” or illuminate the malfunction indicator lamp (MIL).

What are the common causes of code P0512 ?

Depending on year, make, and model, DTC P0512 may have number of causes. Here are some of the most common.

  • Antenna Ring – A faulty antenna will not receive the transponder signal very well, leading to this problem.
  • Fob Battery – Some smart keys, particularly those for push-button-start vehicles, use a battery to amplify the transponder signal.
  • Main Battery – If the battery is weak or poorly connected, insufficient system voltage can play havoc with a number of vehicle systems, not the least of which is engine starting, which requires the most energy.

What are the symptoms of code P0512 ?

Depending on vehicle and failure mode, you may not notice any problems at all, even if the MIL is illuminated. You may experience starting problems, such as delayed starting or extended cranking, cranking but no starting, or no cranking and no starting.

How do you troubleshoot code P0512 ?

Because one of the fault modes is cranking but not starting, many misdiagnose P0512 as a fuel and ignition system problem, that is, a problem in the fuel pump, fuel injectors, or ignition coils. Unless there are DTCs for these systems, do not touch them until you have P0512 properly diagnosed and repaired.

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That being said, aside from a DVOM (digital volt-ohm meter) and basic scan tool, there are very few things that a DIYer has access to for this diagnosis, as a factory scan tool is needed to access the engine immobilizer system.

  • Check Battery Voltage – With the vehicle off, using your DVOM (digital volt-ohm meter), you should measure a minimum 12.6 V at the main battery. Additionally, check for the same voltage in the main fuse box and engine and body grounds.
    • If the battery measures less than 12.5 V, this may not be enough voltage to sufficiently power all the electronics on starting, which can lead to generation of this DTC. Replace the battery if necessary.
    • If you measure less than 12.5 V between the main fuse box and the engine block or body ground, you may have a poor battery electrical connection. Check for voltage between the body ground and the battery negative (–) terminal, and check for voltage between the fuse box and battery positive (+) terminal. If you detect any voltage, you may have corrosion or a loose connection in a terminal, clamp, or ground strap. Repair as necessary.
  • General Electrical Check – Inspect the electrical system, checking for loose or corroded connections or damaged wire harness. Check all fuses, as well. Focus on the wiring to the ECM and ignition (in the steering column or dash, not the engine). Adjust or repair as necessary.
  • Key Battery – Many smart keys and some mechanical keys may have a small battery to amplify the transponder signal. Batteries are economical enough that replacement could be considered part of the diagnosis. On push-button-start vehicles, you can test this by holding the key fob up to the button, as the antenna is usually located in the button. If the car starts, suspect the battery.
  • Antenna – On some applications, the antenna is simply a ring mounted on the ignition cylinder. This is another part that tends to be fairly inexpensive and a known problem item. Some suggest simply replacing it as a matter of course, but real diagnosis is best left to the professionals.

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Codes Related to P0512

  • DTC P0513 Incorrect Immobilizer Key
  • DTC P0633 Immobilizer Key Not Programmed

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