Technical Description of OBD-II Trouble Code
Performance Issue in Cold Start Idle Air Control System
What does that signify?
This generic powertrain diagnostic trouble code (DTC) is applicable to various OBD-II vehicles, including Hyundai, Subaru, Suzuki, Mazda, VW, Honda, Kia, Cadillac, Nissan, Audi, etc.
A stored code P050A indicates a problem with the idle air control (IAC) system, as detected by the powertrain control module (PCM). The term “cold start” refers to an engine drivability strategy that is only implemented when the engine is at or below ambient temperature.
The IAC valve, controlled by the PCM, is responsible for regulating air flow through the throttle body and into the engine intake manifold during idle.
When the throttle plate is closed, very little air is allowed to enter the engine through the throttle bore. This miniscule amount of air causes the engine to idle roughly. To achieve a smooth idle, a steady supply of vacuum is ineffective due to variations in atmospheric pressure and engine temperature. Therefore, an automatically adjustable method for varying idle air is necessary, which is fulfilled by the IAC valve.
The IAC valve is an electronically controlled valve mounted on the throttle body. It consists of a single housing with an electric motor and two small air chambers. These chambers have a cone-shaped valve and seat between them. The IAC is positioned near the throttle bore, with one chamber aligned with an intake opening outside the throttle plate (inlet chamber) and the other chamber aligned with an intake opening inside the throttle plate (outlet chamber). When the valve is pushed flush into the seat, no air can pass between the two chambers. As the valve is lifted off the seat by the electric motor, ambient air can be drawn through the inlet and outlet chambers and into the intake manifold.
Idle Air Control (IAC) Valve:
The PCM utilizes input data from the crankshaft position sensor and camshaft position sensor to calculate engine RPM. The engine idle speed is programmed for a specific RPM level, and the PCM uses the IAC motor to achieve it. If the actual engine RPM is higher than the desired RPM, the PCM outputs a voltage signal to the IAC motor, causing the motor to extend the valve into the seat and restrict air flow to the engine. This decreases the RPM level. Conversely, if the actual engine RPM is lower than the desired RPM, the PCM emits the opposite voltage signal, causing the motor to retract the valve from the seat and allow more air to enter the intake. This increases the RPM level. The PCM precisely and aggressively targets the desired RPM level, resulting in very small continuous movements of the valve.
If the PCM is unable to effectively control the engine RPM level during cold start, a code P050A will be stored, and a malfunction indicator lamp (MIL) may illuminate. Multiple failures may be necessary for MIL illumination.
What is the severity of this DTC?
A code P050A should be considered severe because it can negatively impact engine drivability.
What are some of the symptoms of the code?
Symptoms of a P050A engine code may include:
Cold car:
What are some of the common causes of the code?
Possible causes for this code include:
What are some P050A troubleshooting steps?
If there are any ECT-related codes stored, it is recommended to diagnose and repair those issues before attempting to diagnose the P050A code.
For Ford motor company products with a stored code P050A, if an audible tap or pop is heard under the right conditions, suspect a defective IAC.
To diagnose a code P050A, you will need a reliable source of vehicle information, a diagnostic scanner, and a digital volt/ohmmeter (DVOM).
Successful diagnosis of a code P050A requires component testing procedures and specifications, wiring diagrams, connector face views, connector pin-out charts, and diagnostic flow charts, which can be found in your source of vehicle information.
A visual inspection of the IAC valve, wiring, and connectors may provide a quick diagnosis. Check for any varmint damage on the wiring harness atop the engine.
If the IAC valve and seat are carbon fouled, the valve may not seat properly. Cleaning the valve may be possible on some vehicles, but follow the manufacturer’s recommendations carefully.
Use the DVOM (ohms) to test the IAC motor. Disconnect the motor from the harness and measure the resistance using the test leads. If the IAC motor does not comply with specifications, it is faulty.
If the IAC motor is within specs, reconnect the IAC motor connector. Use the test leads of the DVOM to probe the input voltage circuit and ground of the IAC connector. If the voltage is within specifications and a ground is present, suspect a faulty IAC valve/motor.
