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'97 Ford Contour - 5 questions

What’s the best way to troubleshoot exactly what is wrong with my AC

My lights keep dimming and coming back as I drive. Could this be connected to my check engine light being caused by my Cat. Converters and O2 sensors?

How many O2 sensors and Cat Converters does my car have? I’ve looked all over and can’t find it. I’ve found some for downstream/upstream and front/back. Are they the same?

There’s a loud hum coming from the engine intermittently when I start the engine and it goes away without coming back when I accelerate. Checking the engine when it happens, there’s a pretty strong vibration on top of the intake.


ok… 4 questions

For lights dimming and coming back, I would do an alternator output test, to determine if you are getting proper voltage to recharge battery first. Could be a bad or old battery, but check alternator output first. Don’t think this situation is related to check engine light, cat converter or O2 sensor.

You never did say what is wrong with your AC, so that may be question #5.


My AC isn’t cold. I haven’t checked the freon. I’ll do that first, but not sure how/what to ckeck beyond that.

It may be best to take your car to an ac specialist and let him do all the testing. I am not familiar with the Contour, but if you put your AC on high output, open up the hood, and then see if the compressor is actually working. Usually the compressor should turn on and off on a cyclic basis. Also look for oily leaks around fittings and the compressor. Your issue could be something like a pressure switch, a system leak, or a bad compressor. Cost to repair varies substantially among those three possibilities.

A full diagnosis will give you the answers you are seeking. Do not be surprised if multiple leaks and issues are found. Your 97 is reaching the time when some AC systems develop multiple problems, due to age.

the two items (dimming lights and o2 sensors are unrelated.

however if you are still running around with the cel light on, how would you know if there are any new error codes?

the purpose of the light is to fix the problems as they crop up, not to lett them build up until there are so many you can’t distinguish which are which.


th eo2 sensor(s) are located in the exhaust pipe. usually one is in front of the cat, in the actual exhaust manifold. and one is just after the cat, before the bolt on flex joint in front of the muffler.

why not start getting the codes read, and tackle that stuff first. write the codes back here. not your shorthand, but the actual codes.

I’ll do that. Thanks.

Well, riding with the cel light on isn’t intentional. I just don’t have the money to buy new O2/Cats. Once I do, I’ll have to take it to my mechanic for him to install, and that will cost even more. I don’t have a reader yet, and so would not be able to post the codes. I’ll see if I can get one though.

So if I have 2 cats, I should have 4 O2 sensors? How do I know which ones to buy? Are the universal O2 sensors really universal? Thanks for the help!