OBD2 Trouble Code P2509

OBD2 Trouble Code P2509

Powertrain control modules, or PCMs, are the brains of modern engines. If these computers experience an issue, usually they will prevent your car from running altogether. It’s crucial to make sure your battery is charged, the battery connections are good, and you have access to an OBD2 scanner if your car won’t run at all.

What Does P2509 – “ECM/PCM Power Input Signal Intermittent” Mean?

What Does P2509 – “ECM/PCM Power Input Signal Intermittent” Mean?

As mentioned above, the PCM is responsible for managing all the systems attached to your motor. If it isn’t getting adequate power, it can not function correctly, and it produces this code. Specifically, the power input intermittent part of the code means that the PCM is not getting enough constant amperage.

When the PCM doesn’t get enough power, it protects itself by shutting down. That’s why your engine won’t run at all. Fortunately, the PCM power supply is redundant, so even if it isn’t getting as much power as needed, you can still read the codes.

How Serious Is Code P2509?

The P2509 code is fairly serious because anything involving the PCM is somewhat serious. It’s an essential part of your vehicle, and they are very expensive to replace. Fortunately, a faulty PCM is only one cause of this code. Oftentimes a much more simple electrical problem is the culprit, and those are much less serious.

You probably won’t be able to drive at all with a PCM error. However, as usual, stop driving if you experience the following issues.

Stop Driving

  • If the car’s performance is suffering greatly
  • You hear unusual engine noises, especially knocking or loud clunks


  • Engine won’t start despite cranking
  • Engine won’t even crank
  • Check engine light flashes
  • Engine stalls and has trouble starting
  • RPMS vary greatly during idle
  • Voltmeter on dash has erratic readings


There are, unfortunately, many causes of a PCM power supply issue. They generally fall into one of three categories.

Wiring or Connection Issues

The most common problem is a bad connection between the battery and the PCM. The following issues could be the root of the problem.

  • Broken wire
  • Excessive corrosion
  • Damaged connectors
  • Improper grounds
  • Broken or disconnected battery terminals
  • Inline components like fuses or diodes have failed

Charging or Voltage Issues

There are two components in charge of keeping power flowing to all the components on your engine. First is the battery. Your battery should produce between 12 and 14 volts and be capable of sending out the cold cranking amperage. If it’s damaged, low, or very old, it may not be able to produce the voltage required for the PCM to run correctly.

The other component involved in powering your car is the alternator. If your voltage regulator is bad, or the alternator has failed completely, it won’t be able to power the PCM. However, you will probably notice other issues before the PCM loses power. You can read about voltage regulator issues here.

The Computer Is Failing

There are a handful of different names for the engine management computer. Some manufacturers refer to it as an ECM, or engine control module. Some use the term ECU, engine control unit, and many modern cars have the aforementioned PCM, which combines the transmission control unit with the engine control unit.

Regardless of which computer your car is equipped with, it can fail. Fortunately, that’s fairly rare. Unlike your home computer, most computers on cars are very overbuilt and difficult to damage. However, it is a possibility.


The solution is going to largely depend on what component has failed. If you follow the steps we laid out, you should be able to isolate the problem quickly. Once you have the problem isolated, you simply need to replace the offending part.

  1. Test the battery using a multimeter.
  2. Visually inspect the battery cables and terminals.
  3. Check for a bad ground.
  4. Visually inspect the wires and connections between the PCM and the fuse box.
  5. Check for bad fuses.
  6. Look for other symptoms of a bad engine computer.

Once you have repaired the broken connection or replaced the bad part, you may need to reset your computer before the code clears entirely. Use an OBD2 scanner, like these we recommend, in order to first clear the code. Then go for a drive; just keep an eye on the RPMs and let someone know where you are going just in case the problem returns.

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