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Ask the Auto Doc: Carbon Buildup on direct injection CTS

A manufacturer's photo of the 2010 Cadillac CTS.

A manufacturer's photo of the 2010 Cadillac CTS. Credit: GM

Dear Doctor: I have a 2010 Cadillac CTS 3.0-liter with direct injection and only 17,000 miles on it. Most of my driving is local. I have heard that direct injection engines suffer from carbon buildup on the valves. My thinking is that a gas treatment won't be of benefit since the fuel doesn't pass the valves on the way to the cylinder. Would installation of a catch can in the PCV system be recommended? Is carbon buildup an issue with DI engines? -- Ron

Dear Ron: Carbon buildup is and has always been a problem. Now with Direct Injection we are seeing a faster buildup of carbon. I do recommend the use of a good fuel additive monthly with the use of premium gasoline. As for any bolt or add-on equipment, I think it's worth a try. -- Doctor

Dear Doctor: I recently inherited a Mercedes-Benz S550 with 22,000 miles from my parents. They were elderly and only changed the oil once in six years. I would like to have the transmission fluid changed properly, as well as all fluids. I am hesitant to go to the dealer since the car is not under warranty. However, if you think the car should be serviced there I will understand. -- Andy

Dear Andy: We service a lot of vehicles and also perform scheduled maintenance. This includes changing of fluids with factory fluids. You can check with your local AAA office for a list of AAA-approved shops in your area. You can also get a price quote from the dealer. In many cases, dealers will negotiate their pricing to get your car into the shop. -- Doctor

Dear Doctor: I have a 2003 Toyota 4Runner V6 with 93,000 miles. I took it in for an oil change and was told the battery was not putting out enough power; so I was fine having it replaced. I drive it away and all of the sudden my rear wiper and defroster are not working. Somehow replacing the battery restarted the computer and the back liftgate no longer worked either. Now the ECU module needs to be replaced for $300. And, the Traction Control and Variable Speed Control are OFF. The cost is over $2000 for the VCS Traction Computer module. So $2,300 in "problems" from a $30 oil change. Help. -- Aaron

Dear Aaron: Before a battery is disconnected a battery backup has to be connected -- and this is not a 9-volt battery plugged into the cigarette lighter. The battery backup is usually plugged into the ALDL connector under the dash. Without doing this step the vehicle computer will lose memory. The make/model/year of the vehicle determines how the computer and/or modules, including the radio, navigation, power windows and automatic transmission will be reprogrammed. As for your problems after the battery replacement, I would also look at the battery terminals for any melt damage to see if the battery may have been connected backwards, which would cause electrical issues. -- Doctor

Dear Doctor: I am the original owner of a 2009 Mercedes E350 with only 6,500 miles. I had the oil changed at 2,000 and 5,000 miles.  According to the owners manual and the dealer, the car should have all fluids (brake, transmission, etc.) changed at the 5-year full maintenance interval. Is this necessary since the car is rarely driven? -- Mike

Dear Mike: Your five-year-old car has very low mileage. If the car is kept in a garage and only driven in fair weather conditions, then I would wait until the car hits 10,000 miles for the full fluid service replacement. At the time of the fluid change, use only the factory fluid. -- Doctor

Dear Doctor: I own a 2012 Nissan Murano. Recently, I've been experiencing problems with the internal temperature controls. Sometimes with the temperature set at 62 degrees it gets too warm inside the vehicle that I have to drive with the windows open. This even happened during the "polar vortex." The Nissan dealer checked it and said nothing was wrong with it. I refused to accept that. The car is still under warranty. Your suggestions please. -- Audrey

Dear Audrey: Today's vehicles have multiple computers and control modules for all systems, including the heating and air conditioning systems. In some cases the system will set a fault code when there is a failure. If there is a malfunction like you describe in your vehicle, then the system may not set a fault code. An ASE-qualified technician can look at all the system sensor values to find the sensor that is out of range. -- Doctor

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