What Does P0508 Mean?
The idle air control (IAC) system circuit is reporting a voltage or duty cycle below the expected minimum threshold. The PCM detects that the IAC motor or solenoid is either not receiving power or the feedback signal is too low. This typically results in the engine stalling at idle or idling very low because the IAC cannot open the bypass air passage.
Common Causes
35%
Failed IAC valve motor with an internal open circuit or short to ground
25%
Open or high-resistance wiring in the IAC control circuit
20%
Corroded or damaged IAC connector causing poor contact
12%
PCM driver circuit failure for the IAC output
8%
Poor ground connection at the IAC or PCM ground point
Diagnostic Steps
1
With the key on and engine off, use a multimeter to check for power supply voltage at the IAC connector — typically one pin should have battery voltage or a switched 12V supply.
2
Measure the resistance of the IAC motor windings at the valve connector — compare to manufacturer specification (typically 7-13 ohms per winding for a stepper motor type).
3
Check for continuity between the IAC connector and the corresponding PCM connector pins — resistance should be less than 2 ohms with no opens.
4
Command the IAC to various positions using the scan tool's bi-directional controls — listen and feel for the IAC motor actuating. No movement confirms a failed valve or circuit.
5
Inspect and clean all PCM ground points — a poor ground can cause low voltage readings on multiple circuits.
Estimated Repair Cost
$75 - $300
Parts + labor, varies by vehicle and location
The idle air control (IAC) system circuit is reporting a voltage or duty cycle below the expected minimum threshold. The PCM detects that the IAC motor or solenoid is either not receiving power or the feedback signal is too low. This typically results in the engine stalling at idle or idling very lo...
The most common cause of P0508 (Idle Air Control System Circuit Low) is: Failed IAC valve motor with an internal open circuit or short to ground
Typical repair costs for P0508 range from $75 to $300, depending on the vehicle, location, and whether you do it yourself or go to a shop.
The engine may stall at idle, which can be dangerous in traffic situations, especially if it results in loss of power steering and reduced brake assist. The vehicle may be difficult to drive in stop-and-go conditions. Repair before driving in heavy traffic.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0508 to identify the root cause.
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Quick Info
Category
Powertrain
System
Idle Control System
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
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