Code Definition

P1191 — Intake air duct leak

System: Powertrain  |  Type: Manufacturer-Specific  |  Make: GM

About P1191

P1191 is a manufacturer-specific powertrain diagnostic trouble code recorded for GM vehicles. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

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.

P1191 is a manufacturer-specific code. The same code string on a different make may have a different meaning. Always confirm the code's definition against the vehicle's service information for the specific make and model under test.

Code Information

This fault code is triggered when the Engine Control Module (ECM) detects unmetered air entering the engine through a leak in the intake air duct between the mass airflow (MAF) sensor and the throttle body. Air entering after the MAF sensor is not measured, so the ECM miscalculates the fuel mixture, which can cause rough idle, hesitation, stalling, and a lean condition at idle that may richen up off idle. The ECM identifies the problem by monitoring MAF data and fuel trims and comparing them against expected values. A large duct leak can also allow unfiltered air and dirt into the engine.

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