P0508 Idle Air Control System Circuit Low

P0508 indicates a low condition in the idle air control system circuit. The controller sees lower than expected voltage, current, or feedback in the IAC control path.

Code details

Generic OBD-II · P0

System: Speed / Idle
Code type: Generic (SAE / ISO controlled)
Standard: SAE J2012 / ISO 15031-6

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not clean or replace the idle valve before checking the low circuit condition and intake air leaks.

Symptoms of P0508

Unstable, high, or low idle, or stalling.
Erratic speedometer, cruise-control, or shift behaviour.
Check-engine light with a hesitation or surge.

Common causes of P0508

A dirty throttle body, idle-control valve, or throttle-position sensor.
A failing vehicle-speed or wheel-speed sensor, or its wiring.
Vacuum leaks or a related sensor forcing the idle/speed strategy.

Useful checks before replacing parts

Check idle air control command, control voltage, current draw, idle speed, throttle position, intake airflow, and freeze-frame idle conditions.
Inspect for short-to-ground faults, open power feed, damaged IAC wiring, connector corrosion, carbon buildup, vacuum leaks, and sticking idle control hardware.
Command the IAC or idle actuator with a scan tool and confirm both circuit response and actual idle speed change.

Related OBD-II codes

These nearby speed / idle entries can help compare wording and pin down the fault area.