Dr. Gizmo Column

 "Dr. Gizmo"

By Phil Arendt
 

Dash Goes Blank

 

Question 1

The dash in my 2008 Cadillac DTS goes completely blank. It’s an intermittent problem that is covered under the warranty. I have been in contact with my dealer and General Motors but they do not have an idea how to fix it. I’ve seen similar problems posted on the internet, but there is no repair. How can I get this problem resolved? R.A., Marengo, IL.

 

Answer 1

Total the car. All kidding aside problems such as this generally are due to a fault in the body control module or ground connections. More than likely the trouble in your car is due to a poor ground.

 

As for your dealer or General Motors not knowing the cause or how to fix the trouble, they won’t know what to do until a technician performs diagnostic tests and probes the circuits. He or she must check the ground connections and connections at the control module. Once this is accomplished a technician will be able to decide what needs repair or replacement.

While it’s possible a control module or even the instrument panel has a fault, all ground connections should be carefully examined before components are replaced.

 

Bad Switch Might Be The Trouble

Question 2

I have a 2010 Dodge Avenger SXT with a non-functional cruise control. My car has 57,000 miles. When I turn on the switch the cruise control light turns on but it won’t set any desired speed. A mechanic checked for codes and tested the brake light switch. There were no trouble codes and the brake light switch is working fine. He does not know what causes the trouble.

Do you have any idea what is wrong? T.C., email

 

Answer 2

Sure, there is a loose nut behind the steering wheel. All kidding aside a check of a professional web site found several issues regarding the cruise control switch. A few technicians explained symptoms that are identical to yours. In their quest to repair they discovered that the switch had partially come apart. One technician went so far to say that the switch was poorly designed and cheap. The fix was to replace it.

Once your technician removes the air bag module he may find the same trouble.

 

 

Interior Accessory Trouble

Question 3

I’m having trouble with the interior lights and other functions in my 2004 Nissan Armada. I took the vehicle to a repair shop where they determined that the body control module was damaged by a shorted wire. The technician wants to replace it but it’s expensive. I did not have it replaced.

I was talking to a friend about the problem. He suggested that I get a module from a junk yard. I called two yards and both of them have a module for a lot less money than my shop. If I replace the bad module with a used part will I need to do anything else? D.R., email

 

Answer 3

It’s iffy. Sometimes a used module works and sometimes not. If you are willing to take a chance, the worst that could happen is that it won’t work. Before you decide to give it a try ask your salvage yard if they will take the module back for a full refund if it does not work.

It’s also possible a module will need reprogramming before functions of accessories such as the power door locks and windows return to normal operation. Reprogramming requires specialized equipment that you may find at a well-established independent repair shop or dealership.

 

Worn Valve Impairs Transmission

Question 4

There is a delay in the transmission in my 2004 Mitsubishi Galant GTS. When I shift into reverse or drive it may be 10 seconds before it engages. It feels as though it goes into neutral before it engages. Once it engages it shifts fine and I can drive all day without any trouble except when I have to shift between reverse and drive.

My car has 98,000 miles on it. Does this mean the transmission needs an overhaul? L.W., email

 

Answer 4

This condition may not require an overhaul. At least keep your fingers crossed it won’t. Often symptoms such as this are caused by excessively worn valves. To access the solenoids and valves does not require major disassembly of the unit. Replacing worn valves in the valve body or replacing the entire valve body might be the cure.

 

Lean Fuel Mixture Causes Misfire

Question 5

The 3.0-liter engine in my 2005 Mazda Tribute misfires. I can feel it when accelerating while applying light pressure on the gas pedal. I went to three different repairs shops. One shop replaced the intake plenum gaskets. Another shop replaced the fuel pump and fuel filter. The last shop replaced the spark plugs and ignition coils. Each shop found computer codes 171, 300 and 304. After all of this work the trouble continues. Although it’s in great condition I’m about to junk it, but at this time I can’t afford a replacement.

I bought the car three years ago. It has 138,000 miles. Can you help? T.M., email

 

Answer 5

The diagnostic codes indicate a lean fuel mixture problem, a random misfire and a misfire in cylinder four. Additionally, the symptoms are consistent with a lean fuel mixture. If a technician concentrates on determining the cause of a lean mixture the trouble will be resolved. A lean mixture occurs when there is too much air to fuel entering the cylinders. It appears two shops were addressing a cause for this condition by replacing the intake plenum gaskets, fuel pump and fuel filter. Continued troubleshooting down this path will likely find a cure.

 

A problem such as this might be caused by air leaks in the exhaust system near an oxygen sensor or even a small crack in a vacuum line.

 

Misfire Eludes Diagnosis

Question 6

The 5.3-liter engine in my 2008 Chevrolet Silverado with 88,000 miles is misfiring and the check engine light is on. I went to an auto parts store for a computer test. The partsman found a code for a misfire in one of the cylinders. I bought new spark plug wires and spark plugs because they have never been replaced. After I installed them, the misfire continues.

I returned to the parts store and another test showed the same cylinder was misfiring. The partsman said the trouble might be the ignition coil or fuel injector. He suggested that I go to a repair shop to have the trouble diagnosed.

I went to a repair shop where a mechanic did some tests on the coil and fuel injectors. He did not find any problems. Now he thinks the trouble is inside the engine. He did a compression test and says the cylinder has proper compression. I did not have any more work performed.

The engine continues to misfire. What else could be wrong? R.P., email

 

Answer 6

The results of a compression test are suspicious. Be this as it may, the trouble may be caused by a problem in the valve system. There are a couple of options to determine valve troubles. If your favorite shop has a bore scope a technician might consider a visual examine of the valves through the spark plug opening of the afflicted cylinder to determine a fault. If your favorite shop does not have a bore scope your technician might consider removing the valve cover on the bank of the questionable cylinder. He will check the movement of the rocker arms for proper operation and inspect the valve springs and hardware for any problems. If everything appears normal he should consider removing the rocker arms and then pressurize the cylinder with compressed air to determine if air leaks past the valves into the intake plenum or exhaust system.

If air leaks with the valves in the closed position there is a problem with either the intake or exhaust valve depending upon which system leaks air. If air leaks into the intake plenum the intake valve has trouble. If air leaks into the exhaust system, the exhaust valve has trouble. In either case the cylinder head needs removal to repair the cause.

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 mailto:drgizmo@drgizmo.ws.  ® DR. GIZMO © 1989-2012