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Friday, February 1, 2013

Dr. Gizmo Column


"Dr. Gizmo"
By Phil Arendt
 

Friendly Disagreement, Settled Then Stirred
Question 1

I need your help to settle a bet.  My friend and I were discussing tires.  He said that some tires can’t be rotated.  I disagreed.  All tires need rotation.  What’s your opinion?  D.S., email

Answer 1
Sorry, but your friend is correct.  There are some cars such as the Chevrolet Corvette in which the tires can’t be rotated due to differences in size from front to rear.  The rear tires are larger than the front.   Additionally, many vehicles are equipped with directional tires that can’t be rotated from side to side unless they are removed from the wheels and remounted on the wheels of the opposite side during a rotation.  In such cases most owners just have the front tires moved to the rear and the rear tires to the front and not crisscrossed.  The best rule of thumb for tire rotation is to follow the carmakers tire rotation recommendation outlined in your owner’s guide. 

Now here’s something that might stump your buddy.  Due to more stringent tire standards for replacement the Lincoln penny is no longer a tool to measure tread depth.  For decades if you placed a penny upside down with President Lincoln facing you, if his hairline showed when inserted in the tread a tire needed replacement.  This meant that there was 2/32 inch or less tread remaining.  Now with new tire standards for safety and fuel economy the George Washington quarter has taken the place of the penny.  The measurement for replacing a tire is now 4/32 inch of tread remaining.  The method of measuring a tire with a quarter is the same as with a penny but now if President Washington’s hairline shows the tire needs replacement. 

Shop Lacks Test Equipment
Question 2

My 2008 Mitsubishi cranks when I turn the key but it won’t start.  I cranked it until the battery died and called AAA.  The tow truck driver jumped the battery but it still would not start.  I had him tow the car to my repair shop. 

The car will not start for my shop.  They have done all kinds of tests but cannot determine the trouble.  My mechanic thinks there is a problem in the antitheft system.  He asked if I have another key because that might start the car.  Unfortunately, I purchased the car a little over a year ago and the dealer did not give me two keys.

My mechanic says his tester does not have the capability to communicate with the system and suggested that I have the car towed to a dealership.  Is this my only alternative?  T.R., email

Answer 2
You could have the car crushed at a salvage yard.  All kidding aside, if you are dead set against taking the car to a dealership another independent shop might have the equipment to communicate with the antitheft system and body control module.  To find a repair shop with the proper equipment consider calling a AAA-Approved Auto Repair shop.  Call your local AAA for a list of shops.  One might have the tool to do the work.  If not, the next stop for your car is a dealership and it is possible a Mitsubishi dealership is AAA-Approved.  Also, once the car is repaired consider investing in a second key just in case the present key fails to communicate with the antitheft system.

In A Quandary Over Where To Take Car For Repair
Question 3

A “Service Park Assist” light has turned on in my 2007 Cadillac DTS and the system does not function.  My car has 91,000 miles on it.

Is this something that can be repaired at an independent repair shop or do I have to go to a dealer shop?  T.D.S., email

Answer 3
It all depends upon the repair shop.  Some independent repair shops have the expertise and tools to communicate and program control modules and some don’t.  It’s likely a shop with a great reputation that has been in business for many years will have the tools and a technician that can do the work.  A shop with a great reputation that lacks a particular tool and or expertise to perform an operation will refer you to a dealership or another shop that can handle the task. 

Definitely a dealership will have the tools and technician to diagnose and repair the system.

Runaway Truck
Question 4
Since replacing the battery in my 2003 Chevrolet Silverado 3500 the gas pedal has been sticking.  When accelerating and I reach cruising speed I can release the gas pedal and the truck continues to accelerate for as long as ten seconds.  The first time this happened I thought I had the cruise control on but it wasn’t.  I pulled to the side of the road to make sure nothing was interfering with the gas pedal but the floor mat was not touching nor did the pedal bind when pressing and releasing it.  Since this event the engine has accelerated on its own a few more times so I’m careful to maintain a large interval between my truck and vehicles ahead of me.

I went to a repair shop where a technician examined the gas pedal and did a number of tests.  He drove the truck with a scan tester connected to a computer.  He experienced the acceleration trouble but could not find any problems.  He suggested that I leave it for a few days so he can track down the cause of the trouble.  As of yet, I have not left it at the shop.
Have you ever heard of trouble like this? D.L., email


Answer 4
The gas pedal in your truck operates an electric switch that signals the opening and closing of the throttle on the engine.  Certainly it is possible the switch has a fault but tests should reveal issues that would tell a technician there is trouble. 

Since so far tests have not found abnormalities it is time to consider tests of the cruise control.  He might consider examination of switches and module associated with the cruise control.  Examination of the conductors in the cruise control circuit including ground connections and terminals in plugs is in order. 
Before your technician begins tests he might consider disconnecting the cruise control.  Once this is accomplished a test drive may find the condition does not occur with the cruise disabled.  If so, he can focus on faults in that system and abandon troubleshooting the gas pedal circuit although they are interconnected.

 
Poor Connection Causes Trouble
Question 5 

I have a 1991 Volkswagen Vanagon camper with 107,000 miles.  The vehicle is in great condition and has not given me a bit of trouble until now.  I use the vehicle for camping and during the winter months it is parked in my garage.  Occasionally, during the winter I drive it on nice days to keep it in good working order.  The last time I drove the engine hesitated and bucked as if it was going to stall.  I took it to a repair shop that has maintained it for several years.  A technician has done all kinds of tests and has replaced several parts including the engine control module but the trouble remains.  Now he is at a loss.

I’m not about to give up on this vehicle.  I have always changed the oil every 3,000 miles or 3 months and follow the factory service schedule for everything else.  Do you have any suggestions?  P.W., email

Answer 5
It’s a good thing this problem did not occur during a camping trip.  It certainly is not time to dump the camper.

At this stage of repair ask your technician to consider a thorough check of all the electrical ground connections.  As a vehicle ages, ground connections are prone to suffer from corrosion or become loose.  When this occurs unusual driveability conditions develop that can stump even the most experienced technician. 

Once he examines the ground connections it is likely he will find the cause of the trouble.  Renewing a good electrical path at a ground circuit will likely place your trusty VW back into service as your mode of transportation to your next camping destination.

New Fuse Might Fix Trouble
Question 6

Yesterday, I went to start my 2000 Dodge Durango with a 4.7-liter engine.  It cranked and cranked but would not start.  Thankfully I have a second car so I could get to work.  After work I tried to start it and it just cranked.  Then I realized the odometer had a message that said “P done”.  Also, the interior lights and power door locks do not work. 

My Durango has 160,000 miles on it.  It usually runs fine.  I don’t want to put a lot of money into it.   Do you have any idea what the trouble is? P., email

Answer 6
The message decoded means let me pass in gracefully.  All kidding aside, this might be an easy repair.

Your truck sent a message to the odometer that means no codes.  Since the interior lights and power locks do not work, this could mean that there is no power to the body control.  The body control module sends a code to the engine module to start.  Check the fuses.  You might find the fuse for the power door locks is open or blown.  If so, replacement could get your truck back on the road.  If a new fuse blows there is a short somewhere in the circuit that needs troubleshooting.  If it doesn’t blow, you’ll likely jump for joy when your truck springs back to life. 

Keep your fingers crossed that a new fuse does the trick.

Thanks for all of your great questions.  Dr. Gizmo can’t wait to answer more.
Phil Arendt is a columnist, consultant and A.S.E.-Certified Master Technician.  Readers may send questions to Dr. Gizmo at P.O. Box 548, Cary, IL. 60013 or e-mail address drgizmo@hotmail.com  01/14/2013 ® DR. GIZMO © 1989-Present

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