What do these check-engine light codes mean?

The Car Doctor answers automotive questions from readers.

A CarMD report found New England is the cheapest place to fix problems that lead to a check engine light.
A CarMD report found New England is the cheapest place to fix problems that lead to a check engine light. –Eric Fleming Photography / Shutterstock.com

The check-engine light came back on again in my car. What should I do?

Q. The check-engine light was on in my 2003 Ford Windstar, so I took it to a shop and they said all of the oxygen sensors were faulty. They replaced the sensors, and the van runs better than it has in a long time, but the check-engine light came back on again with the codes P0174 and P0171. The shop now tells me my van will need a very expensive computer. What should I do?

A. I think the shop could have misdiagnosed the problem. Although the codes indicate a problem with fuel, the issue is more likely related to a slight leak in the intake manifold that causes a lean running condition. Historically, replacing the intake manifold gasket/O-rings solves the lean running problem, and the check-engine light will go out.

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John Paul is AAA Northeast’s Car Doctor. He has over 40 years of experience in the automotive business and is an ASE certified master technician. Email your car question to jpaul@aaanortheast.com.