1998-2001 Jeep Cherokee XJ: Evaporative Emissions Control System explained - How it Works and Where the Leak is + Test it Without a Smoke Machine! [‘98-’01 XJ] P0455 Large EVAP Leak
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The Evaporative Emissions Control System is a vacuum actuated air filtration system connecting the fuel tank to a charcoal canister, to a purge valve, to the intake manifold. Along the way is a Leak Detection Pump, also run by engine vacuum, with its own air filter.
The purpose of an EVAP System is to reuse unburnt fuel vapors residing in the gas tank. This improves both your Mileage and Range, as less fuel is wasted from naturally evaporating.
The 1998-2001 Jeep Cherokee employs one such system, and was among the first vehicles to do so. As a result of its primitive and unrefined nature, it’s a very common cause of the Check Engine Light, often displaying P0455. There are a handful of reasons this error can happen, documented in this video.
An EVAP leak isn’t necessarily a bad thing, it just means you’ll get worse fuel economy but no harm will usually come of it. However, many states require annual emissions inspections, and if your Check Engine Light is on during said inspection you’ll be unable to register the vehicle until the problem is fixed, so let’s track it down.
If you have any questions, don’t hesitate to ask. Worst thing that can possibly happen is me not knowing the answer.
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