Idle Air Control Circuit Low leads to the error code P0508. This indicates that the idle air control system circuit is too low, causing inconsistency in the engine’s idle RPM. Read to know more about the P0508 error code.
This is a generic error code, applicable to all OBD-II-equipped vehicles manufactured between 1996 and the present. It is a common error seen among Chrysler, Dodge, Hyundai, Mazda, and Jeep models. The troubleshooting and repair procedures will vary depending on the vehicle’s make and model.
What is the P0508 error code?
A linear servomotor controls a plunger that regulates the amount of air allowed to bypass the throttle plate and enter the intake manifold as part of the IAC system. Having control over the amount of air allowed to bypass the throttle plate aids in regulating the engine’s idle RPM.
When the throttle plate is idle, the throttle body allows very little air to enter the engine. This amount of air is insufficient for the engine to continue idling, and it will certainly stall. A source of supplementary air (vacuum) is required for the engine to continue to idle with the throttle plate closed.
Obviously, when the throttle plate is opened, the auxiliary vacuum source would be detrimental to engine performance and fuel economy (upon acceleration). Hence the requirement for a PCM-controlled vacuum source with complete adjustability. The plunger housing of the IAC valve is designed with two separate air passageways.
Typically, the IAC valve is attached to the intake manifold near or on the throttle body. It is positioned so that ambient air can flow through it and into the manifold when it is open (when the plunger moves out of the opening), but cannot flow through it when it is closed (when the plunger fills the opening).
The IAC is in constant motion, controlled by the PCM. The PCM determines how much air should be permitted to bypass the throttle plate based on input signals from the oxygen sensors, throttle position sensor, and other sensors. As the PCM adjusts voltage and ground signals to the IAC valve, the valve responds accordingly. If the engine RPM levels do not correspond with the programmed limits, the code P0508 will be stored, and the MIL may illuminate.
Causes
- Malfunctioning IAC motor or valve
- Leaky engine vacuum
- Open IAC control connectors or wiring.
- Accumulation of carbon in the throttle body or IAC valve
- PCM malfunction or error in PCM programming
Symptoms
- High RPM level Engine stalling, particularly at idle
- Unusual sounds from the area of the throttle body
- Additional IAC-related codes
Diagnosis
Connect an OBD-II scanner to the vehicle’s computer system in order to diagnose this code. Check for the presence of additional codes, record the data, and then reset the codes. Drive the vehicle to see if the error code reappears. If the code returns, begin investigating potential causes, such as the IAC.
Check the bore of the throttle body. Ensure that you clean it. Then, reset and observe if the code reappears during the test drive. Clean the IAC’s electrical connections and circuits to ensure proper operation. As required, repair or replace connections such as burned, corroded, or damaged electrical connectors.
Check the engine for vacuum leaks that may be contributing to the engine’s uncontrollable RPM. Correct vacuum leaks and recheck the system. In most cases, it may be necessary to replace the IAC. Or, the PCM can be replaced, though this is an extremely uncommon option.
Possible fixes for the P0508 error code
- Depending on the diagnosis, common repairs include the following:
- Repair or replacement of the faulty IAC system electrical connectors
- Fixing vacuum leaks
- Substitution of the IAC
- Alteration of PCM (rare)
How serious is P0508
P0508 is a signal that you should not disregard. If the idle RPMs are too high or too low, it can cause severe damage to other engine components and prevent the vehicle from operating properly.
If the vehicle hesitates, stutters, or loses power during acceleration, it can cause extensive damage to other engine components and prevent the vehicle from operating properly. Having a vehicle that surges while driving is extremely hazardous and should be resolved as soon as possible.
Cost of diagnosing the P0508 error code
However, we can estimate a price range for parts and labor. The cost of repairs will depend mostly on the nature and extent of the work performed.
The IAC may only need to be cleaned and reset, which typically costs between $75 and $100. However, if the problem is more severe or if other issues (such as wiring repairs) need to be addressed, labor and part costs will increase into the $300s and $400s.
Replace the PCM: $200 to $700 for labor plus $150 to $900 or more for the part (s). If you are also replacing relays, sensors, or other modules along with the PCM, you can expect to pay an additional $50 to $150 for each one. Lastly, if wiring or other issues are discovered during the diagnostic process, expect to pay an additional $100.
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