Code Definition

P0508 — Idle Speed Control Valve Circuit Low

System: Powertrain  |  Type: Generic (OBD-II Standard)  |  Make: Generic

About P0508

P0508 is a generic (obd-ii standard) powertrain diagnostic trouble code. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

When P0508 is stored, the module has detected a signal or supply voltage lower than the expected operating range.

Scanning & clearing: A generic OBD-II scan tool will usually read and clear powertrain (P) codes. For live data, freeze-frame capture, and bi-directional tests you may need a more capable scan tool that supports the vehicle's ECM protocol.

Because P0508 is a generic OBD-II code, its base definition is shared across manufacturers. The specific diagnostic steps, reference values, and repair procedures can vary by vehicle, and the TaT Diagnostic Assistant includes verified procedures submitted by working technicians.

Code Information

The P0508 fault code is set when the Engine Control Module (ECM) detects a lower than expected voltage or input signal in the circuit of the Idle Speed Control (ISC) valve, also known as the Idle Air Control (IAC) valve in some vehicles. This valve regulates the engine's idle speed by controlling the amount of air that bypasses the throttle plate when the engine is idling. A low input signal in the ISC valve circuit can indicate an electrical issue, such as a short to ground, a malfunctioning ISC valve, or problems with the wiring or connectors. This condition can lead to a range of idle-relat...

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