Car Doctor Q&A: Why Is My Ford Explorer Check Engine Light On?

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Occasionally, readers write in to AAA Car Doctor John Paul with questions that are so common to certain vehicles that there should be an addendum to the owner’s manual to learn how they’re fixed. This Explorer owner has one of those issues.

Q. I have 2000 Ford Explorer with the 4.0 liter engine that I use almost like a pickup truck. I carry stuff from the home improvement store, my canoe, dogs and even my kids from time to time.

The problem is a check engine light and multiple codes. The codes indicate a misfire and lean condition, The codes that keep coming back are PO171 and PO174. Most of the time the truck runs fine not always but most of time. When I first start it up it runs rough.

So far I have replaced the plugs, coils and run a quart of fuel injection cleaner through the fuel system. The truck runs better but the light is still on. Any ideas?

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A. One area that is historically an issue with that engine is that the intake manifold seals leak. The manifold is made of a composite (plastic, in other words) and the seals are a o-ring type.

Over time the manifold loses it seal causing a lean running condition which turns the check-engine light on. When the engine is cold the problem is worse, but as the engine and manifold warm up, the o-rings seal up a bit and the rough running is less apparent.

The best method to test for this problem is with a smoke-machine, but this is a very common source of the problem.

The o-rings are replaceable if you’re handy. There’s a good video series showing how to do it here:

John Paul is public affairs manager for AAA Southern New England. A certified mechanic, Paul tests dozens of new cars each year and also hosts a radio show on AM 950 and 550.