Intake Air Duct Leak Detected (GM)
What does P1191 mean?
The P1191 code means the vehicle's onboard diagnostic system has detected: Intake Air Duct Leak Detected (GM). This is a moderate severity code.
Common Symptoms
- Check Engine Light on
- Whistling or hissing noise from engine bay
- Rough idle
- Poor fuel economy
- Lean fuel trim readings
Probable Causes (Ranked by Likelihood)
- Cracked or loose air intake duct between MAF sensor and throttle body Very High
- Failed air intake duct clamp High
- Torn air filter housing seal Moderate
- Damaged intake snorkel or resonator Moderate
- MAF sensor O-ring leak Low
Step-by-Step Diagnostic Procedure
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Visually inspect the air intake duct from the air filter to the throttle body for cracks
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Check all clamps on the intake duct for tightness
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Look for tears or damage in the rubber bellows section of the intake duct
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Perform a smoke test through the intake to find hidden leaks
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Inspect the MAF sensor mounting seal or O-ring
Frequently Asked Questions
Why does an air duct leak matter?
Air entering after the MAF sensor is not measured, so the PCM does not account for it when calculating fuel delivery. This causes a lean condition that triggers poor running and fault codes.
Is this an easy fix?
Yes. Most air intake duct leaks are caused by cracked hoses or loose clamps, which are inexpensive and easy to fix. A new intake duct typically costs $25 to $100, and installation is straightforward.
Can I use tape to fix a cracked intake duct temporarily?
As a temporary fix, you can use aluminum tape or silicone tape rated for automotive use. However, this is not a permanent solution. Replace the duct as soon as possible, as tape can deteriorate from engine heat.