Diagnostic Trouble Code (DTC): P0518
P0518 code definition
If the PCM has registered an inconsistency in the engine idle RPM; the P0518 code will be stored.
What the P0518 code means
The manufacturer of the vehicle has set an expected RPM that must be registered when the engine is idling. The PCM will read the RPM during idle; if the reading is too high or too low in comparison to the manufacturer’s specifications, the PCM will try to correct the issue by sending commands to various parts of the engine and transmission. If the RPM is not corrected, the PCM will store the P0518 code.
What causes the P0518 code?
This code is very frequently caused by a carbon choked throttle body bore. Other causes may include:
- Shorted, open, or corroded electrical elements in the idle air control valve
- Faulty idle air control valve
- Vacuum leak
- Open or shorted idle air control valve harness
- Faulty PCM (in very rare cases)
What are the symptoms of the P0518 code?
There are several symptoms that a vehicle owner may observe when the P0518 code is stored, including:
- Low or high engine idle RPM
- Stalling at low speeds
- Stalling intermittently when the throttle is released
- Illuminated Check Engine Light
How does a mechanic diagnose the P0518 code?
After an OBD-II scanner detects the P0518 code, a technician should begin with a visual inspection of all electrical components: replacing, reconnecting, or repairing as necessary. They should then clear the code and perform a test drive, checking that the Check Engine Light does not reappear. If the code does reappear, then the mechanic will disconnect the IAC motor from its electrical connector and start the engine. If the code does not reappear after this step, the IAC valve likely has a short, and is to blame.
If this diagnostic step did not uncover the problem, then the mechanic must continue checking the system for various electrical issues until the problem is discovered.
Common mistakes when diagnosing the P0518 code
Many technicians have reported that it is common for the idle air control components to be replaced before the throttle body bore is cleaned; this can lead to wasted money and repair time. It is important to attempt the basic repairs, such as replacing electrical wiring or cleaning the throttle body bore, before replacing major components. It is also important to clear the code and do a road test after each potential solution is attempted. If the most common repairs do not stop the Check Engine Light from reappearing, it can be a sign of an intermittent issue that requires an in-depth inspection and servicing.
How serious is the P0518 code?
If the P0518 code is being detected, the vehicle needs to be repaired as soon as possible. This code indicates an issue that affects the immediate drivability and safety of the vehicle.
What repairs can fix the P0518 code?
For the most part, addressing the P0518 code means fixing faulty electrical components; however, there are other repairs that may need to be done to clear this code entirely. They include:
- Cleaning the throttle body bore
- Replacing a faulty idle air control valve
- Repairing a vacuum leak
- Replacing a faulty PCM, in very rare cases
Need help with a P0518 code?
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