What does it mean?
This diagnostic trouble code (DTC) is a generic powertrain code, meaning it applies to all vehicles from 1996 onwards (Dodge, Chrysler, Hyundai, Jeep, Mazda, etc.). Although generic, specific repair steps may vary by brand/model.
When your OBD-II-equipped vehicle has a malfunction indicator light (MIL) and a stored code P0519, it means the powertrain control module (PCM) has detected a problem with the performance of the intake air control (IAC) idle system. If there are other more specific IAC codes, these should be diagnosed and repaired first.
The IAC system centers around a linear servo motor that controls a piston regulating the amount of air allowed to bypass the throttle plate and enter the intake manifold. Controlling the amount of air bypassing the throttle plate helps manage engine idle speed. When the throttle is closed (at idle), very little air is allowed into the engine through the throttle body. The engine cannot continue idling with this small amount of air and would likely stall. An auxiliary air (vacuum) source must be provided for the engine to keep idling with the throttle plate closed. Of course, the auxiliary vacuum source would be detrimental to engine performance and fuel efficiency when the throttle plate is open (during acceleration). Hence the need for a fully adjustable vacuum source controlled by the PCM.
The IAC valve piston housing is manufactured with two separate openings that allow air to pass through. The IAC valve is typically bolted to the intake manifold, on or near the throttle body. It is positioned so that when open (the piston retracts from the opening), ambient air can flow through it and enter the manifold, and when closed (the piston fills the opening), ambient air cannot pass through.
An example of an idle air control (IAC) valve:
The IAC is rarely fully open or closed but is constantly moving, controlled by the PCM. The PCM uses input signals from oxygen sensors, the throttle position sensor, and various other sensors to determine how much air should be allowed to bypass the throttle plate. When the voltage and ground signals to the IAC valve are adjusted (by the PCM), the valve responds accordingly. If the engine RPM levels do not match the programmed desired limits, a P0519 code will be stored, and the MIL may illuminate.
Related idle air control system circuit trouble codes include:
P0508 Idle Air Control System Circuit Low
P0509 Idle Air Control System Circuit High
P0511 Idle Air Control Circuit
P0518 Intermittent Idle Air Control Circuit
Severity and Symptoms
A malfunctioning idle air control system can cause the engine to stall or idle at an unexpectedly high RPM. This code should be treated as severe and addressed urgently. Symptoms of a P0519 code may include:
High engine RPM level
Engine stalling, especially at idle
Unusual noises from the throttle body area
Other IAC-related codes
Causes
Possible causes of this code include:
Faulty IAC motor/valve
Engine vacuum leak
Open or shorted IAC control wires or connectors
Carbon buildup in the throttle body or IAC valve
PCM programming error or faulty PCM
Diagnostic and Repair Procedures
A good starting point is always to check the technical service bulletins (TSBs) for your specific vehicle. Your issue might be a known problem with a published fix from the manufacturer, which could save time and money during diagnosis.
To diagnose a P0519 code, you would need a diagnostic scanner, a digital volt/ohmmeter (DVOM), and a reliable source of vehicle information (All Data DIY will suffice).
Start by inspecting all wiring and electrical connectors in the IAC system and repair any that are damaged, corroded, or burnt. Also, check the engine for any vacuum leaks that could contribute to uncontrollable engine RPM levels. If you find vacuum leaks, repair them and recheck the system.
Next, connect the scanner to the vehicle’s diagnostic connector and retrieve all stored codes and freeze frame data. It’s a good idea to write this down in case the code is intermittent. Now, clear the codes and test-drive the vehicle to see if the code resets. Obviously, if other IAC-related codes are stored, they should be diagnosed and repaired first. Also, check all technical service bulletins and safety recalls for the vehicle and the specific malfunction. After performing all repairs, drive the vehicle normally and allow the PCM to enter readiness mode before declaring the problem fixed.
As a simple method to test the IAC system, when the engine idle speed is very high, carefully unbolt (to preserve the gasket or seal) the IAC valve from the engine and use a shop cloth and your fingers to control the engine idle speed. If you can control a high idle condition after removing the IAC valve, you know the IAC system is not functioning properly. If you cannot control the idle speed, suspect a significant vacuum leak. Major engine vacuum leaks can include PCV valves/hoses, vacuum hoses, brake booster, check valve or hoses, a stuck-open EGR valve, EGR gasket leak, or an intake manifold gasket leak.
Consult your vehicle information source for the recommended method of testing the IAC motor with the DVOM. Replace the IAC motor/valve if it does not meet manufacturer specifications.
Additional Diagnostic Notes:
Disconnect all associated controllers before testing circuit resistance with the DVOM