Q. I am actually wintering in Florida and hope you can help me with two questions. I went into a few well-known tire shops that seemed to be pushing brake fluid replacement with their brake jobs. Is this necessary? I have been driving for years and have never run into this. My second question is concerning my 10 year old Caddy; can I change to synthetic oil after driving 50,000 miles on regular oil? I enjoy your column in the paper and on-line when I’m in Florida.

A. Years ago, the only time brake fluid was replaced was when a hydraulic component was replaced or due to some sort of contamination. Brake fluid is hygroscopic, meaning it seeks moisture. This moisture can cause rust, which is very detrimental to today’s anti-lock brake systems. Replacing brake fluid when performing a brake repair could limit problems in the future. Additionally, some vehicles have a specific recommendation to replace the brake fluid. Regarding switching to synthetic oil, this is not a problem. Years ago, people would warn against this, saying the oil would cause the engine to leak oil. This is not true, although synthetic oil will find a leak, if one does exist.

Q. I have a 2005 Nissan Frontier and the transmission fluid is foamy and burned. I have not added any fluid. Should I change the fluid and if so, what kind should I use?

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A. Considering the condition of the fluid, I would change it. In addition, transmission fluid tends to foam if the transmission is overfilled. My other suggestion is to use only Nissan fluid. In various bulletins, Nissan warns against using any fluid other than genuine Nissan automatic transmission fluid.

Q. I read your advice each week and thanks for all the information you've posted in the past helping other readers. Now it’s my turn. I am currently in the market for a new car. I was leaning toward a new Honda Accord V6 Coupe. Since then, I've come across a 2009 BMW 335i with 37,000 miles on it. It is at a BMW dealer and is being sold as a pre-owned certified vehicle for about the same price as the Honda. My question, is a pre-owned certified BMW an equal or better option over a Honda Accord?

A. Since the BMW is a certified pre-owned (CPO) car, in my mind it makes all the difference. CPO BMWs are typically the cream of the crop, that have been completely checked out by certified BMW technicians and have additional warranty coverage to six years or 100,000 miles—whichever comes first. The Honda Accord is a great car; the last coupe that I drove handled well, had plenty of power, and returned good mileage. As good as the Honda is if you are a driving enthusiast, the BMW 335 is more fun to drive. Of course, the Honda is front wheel drive and the BMW is rear wheel drive and, in general, the Honda will be better in wintery conditions. Personally I would buy the Honda Accord-it’s new, under warranty and will hold its value well. That said, when it comes right down to it, I recommend you buy the car you will enjoy driving. 

Q. I own a 2001 Dodge Ram 1500 truck. The check engine light comes on and then off and it is now back on. I had a test that showed a code of PO138 which indicates a problem with the oxygen sensor. I contacted the mechanic that services my vehicle and was told a new oxygen sensor may not correct the problem and it could be a computer issue. What do you think?

A. Computer fault codes can sometimes be misleading, even to the best technician. There is a specific troubleshooting procedure that needs to be followed for correct diagnosis and repair. The wiring, connections, and the sensor itself need to be checked before the computer should be considered. I have seen many cases that the heater circuit in the oxygen sensor fails. In these cases, replacing the sensor solves the problem.