#vacuum leak
8 posts in Car Diagnostics blog about "vacuum leak" — OBD-II diagnostics, DTC codes, repair. ← All posts
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P2279: intake air system leak — the code that names the fault
Most codes describe a symptom and leave you to find the cause. This one states the cause outright, which makes the search unusually direct.
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Whistling from the engine bay: leak, bearing or belt
Three very different faults produce a whistle, and they are distinguishable by when the noise appears. That timing is most of the diagnosis.
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P0101: MAF sensor range/performance — why airflow does not match expectation
P0101 is not a dead sensor code. It means measured airflow disagrees with what the ECU calculated. Here is how to tell a dirty MAF from a vacuum leak, a clogged filter and a tired engine.
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P0106: MAP sensor range/performance and the vacuum leaks behind it
P0106 compares manifold pressure against what the ECU expects from throttle position and RPM. Most of the time the sensor is honest and the intake is leaking.
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P0496: excessive EVAP purge flow during non-purge conditions
P0496 means vapour is being drawn into the engine when it should not be. Unlike most EVAP codes it has real drivability symptoms, and a stuck purge valve causes almost all of them.
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P0507: idle speed higher than expected — hunting the vacuum leak
P0507 means the engine idles faster than the ECU commanded and it has run out of authority to bring it down. Almost every case is unmetered air entering somewhere.
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P2187 and P2189: system too lean at idle only
A lean condition that exists at idle and vanishes under load points almost exclusively at unmetered air. The load-dependence is the diagnosis, and it costs nothing to observe.
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P0171 and P0174: lean mixture — seven causes, and why the sensor is not one of them
The most common code after misfires. It means the module is adding fuel and still cannot keep up. Seven causes in order of probability, and how to narrow the search using fuel trims alone.