Service Engine Soon Light

Reader Question

Dear sir,

I have a question regarding a service engine soon light for a Ford Mustang 3.8L V6 with 31,000 miles on it.

My service engine soon light came on and so I thought it had to do with refueling and so I disconnected the negative terminal on the battery but it came back on later. I thought it could be burned out oxygen sensors but Then, I went to Discount Auto and had them check it with their machine that can erase codes and it said “too rich” and I was told it could either be the EGR Valve or the IAC valve.

I replaced the EGR valve but the light is still on. Then I took it took a local mechanic and he got the same reading of “too rich” and he said it wasn’t the egr or iac but that Ford had a service bulletin on the that kind of light and it is a vacuum leak. However, he told me it would be a lot to repair that because of the man hours involved. So, do you know anything about how to correct this problem.

I am no longer under warranty as my 3 years came before the 36,000 miles. I am looking to trade in my mustang for a new one and so I can just disconnect the battery to reset the light prior to trade in. But it doesnt really affect the cars performance, however, sometimes it does kind of chug . If you could help me out that would be great.

Thank you, Jonathan


First thought, if you area trading this car in on a new Ford at the dealer ..I would not worry about the light. I just traded in a car last week on a new one .they did not even drive it. Sooo, before you spend more time and money on this problem, consider the fact that it might not make a difference on trade in value.

Now, on the light itself, it could be on for ANY reason. Any of the 20 or so sensors could be out of whack, or you could have a simple vacuum leak in a rubber vacuum hose somewhere under the hood.

Disconnecting the battery on a new car does not clear all the computer memory out like it did on older cars, so you will need to visit your mechanic to have them clear the memory. If the problem is still happening though, the light will come back on.

You really need to have the computer codes read by a competent mechanic and go from there if you want to repair this issue before you trade it in.

But the money you spend doing that will probably be more than the deduction that they will take for the light being on IF they even care that the light is on. They are interested in selling you a NEW vehicle!!!


Austin C. Davis

Posted in: Check Engine Lights

About the Author:

Austin Davis, consumer car repair advocate. "Hi there! I love to help people solve their car repair problems and I hope my site was helpful to you today. Thank you for stopping by."
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