Underfloor Vibrations Can Have Many Root Causes

June 6, 2010/Steve Tackett


Dear Doctor: I am the original owner of a 2004 Honda Pilot with 103,000 miles. I started to feel a vibration from under the floor and can hear it as well. It usually happens when the car is cruising at about 35-40 mph and seems to happen three times a day, but not every day. I had the tranny checked and no default codes appeared. What may be causing this? Steve
Dear Steve: The vibration you are feeling can be from a number of things. First, a vibration will usually not set a trouble fault code. Now we need to look at the engine mounts for any movement. Next, look at the exhaust for heat shields or worn gaskets with spring bolts included. Even a loose worn fan belt accessory pulley could cause a vibration. We use a tool called a Chassis Ear that is connected to any area that could be in question to help locate hard to find noises and vibrations.
Dear Doctor: I have a 1999 Isuzu Trooper with 160,000 miles. I can engage the AWD system when the vehicle sits all night long, but as soon as I take it out, it will not go back in. My mechanic has replaced the 4WD electrical module control to no avail. Can you help me? Bob
Dear Bob: There is no easy answer for this one. Anytime we have to look at problems such as yours, we go to our Alldata and Identifix resources and look at other Isuzu vehicles with the same condition. Next, we look at the 4×4 system circuit and what makes it engage. A qualified technician should be able to find the problem. The diagnostic time involved could be up to three hours, plus repair labor costs.
Dear Doctor: I purchased a 2009 Chrysler Town & Country minivan that now has 11,000 miles on it and I am already on my third set of front and rear brakes and rotors. The pulsing feel has started again. The dealer has been making all the repairs under warranty, but long term concerns me. What advice can you give me? Ben
Dear Ben: A new 2009 vehicle that has pulsating brake rotors tells me that very poor quality metal brake rotor material is being used. Continue to use up the warranty, and then after the warranty is expired find a different brand. There are many good aftermarket brake rotors that will fix the problem.
Dear Doctor: I own a 2004 Hyundai Elantra sedan with just over 91,000 miles.

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I am the second owner, so my Hyundai manufacturer’s warranty has already expired, since the 5-year/100,000-mile only applies to original owners. I have the oil changed every 5,000 miles since I switched to full-synthetic oil and my maintenance is up to date. I would like your opinion on whether it’s worthwhile to purchase an extended warranty and if so, any recommendations of which one, or what features to look for. Joe
Dear Joe: Some of the companies that offer extended warranties are not worth the paper they are written on. We honor extended warranties at our shops and the first time a customer comes in with one I ask the customer to take a few minutes and read what’s covered and if they are responsible for paying the diagnostic time. Some companies do not cover worn out parts just defective parts, and only pay a small portion of the actual repair bill. You can check with the local AAA office for their suggestions on a reliable company.
Dear Doctor: I was under the impression, perhaps incorrectly, that manufacturers of motor vehicles assembled and sold in the U.S. must, by law, maintain replacement parts for 20 years beyond the date of the last model produced. Please clarify. Herb
Dear Herb: There are no manufacturing laws at present that would have manufacturers make parts available for a 20-year period in the U.S. I have been in the auto repair business for more than 40 years and have seen it all. The auto industry is not the only manufacturing industry that does not have to make parts available; the same holds true for just about anything we buy, including your cellphone batteries. — Junior Damato, Motor Matters

Junior Damato is an ASE-certified Master Technician.

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Copyright, Motor Matters, 2010