What does P1508 mean on a Chevy?

P1508. Idle Speed Low Idle Air Control System Not Responding. Applies to Silverado, Sierra, Tahoe, S-10, Blazer.

What causes P1508 on a Chevy?

Carbon-fouled idle air control valve pintle stuck in the bore Carbon-packed throttle body starving idle airflow on Vortec engines Vacuum leak pulling idle below the IAC correction window Failed IAC motor windings open on one phase

How do I fix P1508 on a Chevy?

Clean the throttle body and IAC passages and perform an idle relearn first Command IAC counts with a Tech2 or GDS2 and watch idle response Smoke-test the intake for vacuum leaks skewing idle control Test IAC motor winding resistance against spec before replacing Replace the IAC valve only if counts do not move idle after cleaning

Code

P1508

Idle Speed Low Idle Air Control System Not Responding

Category: Powertrain - Computer and Auxiliary Controls
Severity: Check Engine Light
Applies to: Silverado, Sierra, Tahoe, S-10, Blazer
Related: No single generic twin. See OBD Codes List

What it means

P1508. Idle Speed Low Idle Air Control System Not Responding. This Chevy-enhanced code applies to Silverado, Sierra, Tahoe, S-10, Blazer.

Findings, check these first

Carbon-fouled idle air control valve pintle stuck in the bore
Carbon-packed throttle body starving idle airflow on Vortec engines
Vacuum leak pulling idle below the IAC correction window
Failed IAC motor windings open on one phase

Standard procedure

Clean the throttle body and IAC passages and perform an idle relearn first
Command IAC counts with a Tech2 or GDS2 and watch idle response
Smoke-test the intake for vacuum leaks skewing idle control
Test IAC motor winding resistance against spec before replacing
Replace the IAC valve only if counts do not move idle after cleaning

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Sources and review

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Last updated 2026-09-19.

Report a correction for P1508. Include your vehicle, the issue and a source if you have one.