P0509 OBD-II Trouble Code: Idle Air Control System Circuit High

check engine light

P0509 code definition

If this code is stored, it means that your vehicle’s PCM has picked up on an inconsistency regarding the RPM of the engine when it’s in idle.

What the P0509 code means

Every vehicle has a set RPM level it’s supposed to be at when in idle as predetermined by the manufacturer. Your vehicle’s PCM is in charge of monitoring the idle RPM to make sure it lands within a certain range. If it finds that it’s idling too high or too low, your PCM’s first response will be to restore an acceptable RPM on its own. However, if it is unable to do so, the P0509 code gets stored. Usually, the Check Engine Light will come on too.

What causes the P0509 code?

There are a few reasons that your vehicle’s PCM may store this code. By far the most common, though, is just that the throttle body bore is being choked by carbon coke. Other culprits you should know about are: * A sizable vacuum leak * A defective idle air control valve * Electrical circuits that are open or shorted Although it’s extremely rare, there’s also a chance that your stored P0509 code could be caused by a bad PCM.

What are the symptoms of the P0509 code?

Obviously, given the nature of this code, you’ll most likely notice that your engine’s idle RPM is much higher or lower than it should be. The former will probably be the more noticeable of the two symptoms because of the loud noise your engine will be making despite having very little demanded of it.

Another extremely obvious clue that something is wrong when a P0509 code has been stored is that your engine will stall out at very low speeds. This will occur even though your accelerator pedal isn’t even pressed down.

Furthermore, when you release the pedal, you may find that it stalls intermittently. Basically, once your vehicle’s RPMs stop performing normally when in idle, you can expect that it becomes much more difficult to drive or slow down as well.

How does a mechanic diagnose the P0509 code?

To diagnose the problem, your mechanic will need an OBD-II Scanner. This will allow them to draw out the P0509 code and any others your PCM has stored. After the mechanic understands all that they’re up against, they’ll continue by inspecting all the connectors and wires that may be involved.

If that doesn’t cure the issue, your mechanic will most likely look in on the fuses for any problems. However, usually, those first two steps are enough for a successful diagnosis.

Common mistakes when diagnosing the P0509 code

The most common misdiagnosis that involves this code is probably when idle air control components get replaced before the throttle body bore is even addressed. Doing this can lead to unnecessary expenses and/or not eliminating the actual problem.

How serious is the P0509 code?

This code isn’t serious insofar as it won’t put your life at risk. In fact, you’ll have a hard time getting your car to even move in many cases. Instead, this is a code that represents an extreme inconvenience. It should be fixed ASAP so you don’t end up stalling out when you’re driving.

What repairs can fix the P0509 code?

The most common repairs for curing your vehicle of P0509 involve addressing problems with the electrical components involved with deciding how many RPMs are appropriate. Another common solution would be cleaning out the throttle body bore. Far rarer would be having to replace a defective PCM.

Additional comments for consideration regarding the P0509 code

A digital ohmmeter can be a very helpful tool for this problem because you can use it to measure circuit resistance.

Need help with a P0509 code?

Do you need help with P0509? Then just complete this online form to set up an appointment with YourMechanic and receive a free quote. You can also call 1-800-701-6230 to speak with one of our service advisors. Simply let us know where you’d like us to send a certified mobile mechanic and they’ll perform all necessary repairs onsite.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

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