Northwest Herald Dr. Gizmo column Dated April 13, 2012

"Dr. Gizmo"

By Phil Arendt

Trans Stuck in Third Gear

Question 1

Two months ago, the transmission failed in my 2007 Mazda 6.  It has 64,000 miles and a 2.3-liter engine.  When the transmission failed the car barely moved and needed a tow.  A shop installed a remanufactured transmission.

Two weeks ago, I was driving when the engine revved up and the transmission would not shift from one gear to another.  I returned to the repair shop where they test drove the car and checked it for trouble codes.  The mechanic found two codes - PO734 and PO841.  He erased them and drove the car.  The transmission shifted normally.  I drove the car and it shifted fine.

Last week, while I was on a road trip the transmission shifted from first to second and third gears but it stuck in third gear and would not upshift.  I was about 600 miles away from home when it happened.  I took the car to an independent repair shop where a mechanic tested the transmission.  He found the same codes as the shop back home.  He erased the codes and the transmission returned to normal.

I continued my return trip without any trouble until I was I about 10 miles from home.  The transmission stuck in third gear once again so I drove home unloaded the car and went to my repair shop.  They found the same trouble codes as before.  Now they are not sure what is causing the trouble.  Do you? M., email

Answer 1

There are several possible causes for the two codes.  The troubles include faulty wiring, a failed oil pressure switch, failed vehicle speed sensor, failed control module, sticking valves or slipping clutches.  If a technician does not find trouble in the wiring, sensors or module he should consider contacting the company that remanufactured the unit and have them send another transmission.  The work should be covered under warranty.

All-Wheel-Drive Makes Buzzing Sound 

Question 2

I hear a buzzing sound coming from beneath the floor of my 2007 Ford Edge with all-wheel-drive, automatic transmission and 3.5-liter engine.  The faster I drive the louder the buzzing is.  It sounds like it is coming from the transmission, but the transmission shifts fine. 

I had the fluid flushed in the transmission, but the noise is still there.  What else could be the cause?  L.K., email

Answer 2

There could be a failure of a bearing in the all-wheel-drive power transfer unit or possibly in the transmission.  The power transfer unit (PTU) delivers engine power to the rear wheels.  It is connected to the transmission so a noise from either unit could lead to misdiagnosis as to which unit has a fault.

Since the transmission is functioning as designed, more than likely the trouble is in the PTU.  If so, it is likely that the unit needs replacement with a remanufactured assembly.

Convertible Fails To Function

Question 3

I own a 2008 Chrysler Sebring convertible.  The top does not go down.  It has a 2.7-liter engine, automatic transmission and 62,000 miles.  As you can see by the miles I like to drive the car, but I like it more when the top goes down.

Recently, when I hit the switch to lower the top the windows went down but the top did not.  Also, a convertible top warning light turned on in the dash.  After this I discovered that the trunk will not open from the key remote or the dash button. 

In an attempt to resolve the trouble I checked all of the fuses, but they look fine.  Is there anything else I should look for? V.R., email

Answer 3

There have been cases of hydraulic fluid leaks from the motor that powers the top.  If you are a seasoned do-it-yourselfer, check it for leaks.  If it is leaking fluid try to determine why and correct the condition.

If there are no leaks, consider asking an experienced technician to test the system.  The technician that is awarded the work needs to have test equipment that can communicate with the convertible top control module.  Since some aftermarket test equipment will not communicate with the module, your chosen technician will have success if he has Chrysler specific test equipment such as a DRB or Witech.

Once trouble codes are retrieved from the module he should not have any trouble determining the cause of the failure.

Backfire Raises Comments From Neighbors 

Question 4

My 1996 Chevrolet Tahoe with 142,000 miles and a 5.7-liter engine backfires when I start.  Once it is running it runs fine.  Since the condition began a few months ago the engine has been tuned with new spark plug wires, distributor cap, rotor, new spark plugs and air filter.  Also, the crankshaft sensor, fuel pump and starter have been replaced.  One mechanic also thought the valves were sticking so he did some tests and examined the valves after removing the valve covers.  The valves seem to be working fine.

The truck is in great condition.  It has never let me down.  Whatever the problem is I will have repaired.  I have to get this fixed.  My neighbors mentioned they hear the backfire when I leave for work early in the morning.  Now my mechanic thinks there is something wrong in the distributor that is causing the backfire.  Does this seem right to you?  L.S.E., email

Answer 4

Watch out!  Neighbors with pitchforks and torches may come to your house.  When your truck backfires they probably duck for cover.  This condition needs a quick repair before the exhaust system blows right off the vehicle. 

Your technician may be on the right track.  Considering vehicle mileage, it is possible bushings on the distributor shaft or the drive gear is suffering from excessive wear.  If this is true, wear can cause the engine to backfire.  Replacing the distributor is the likely approach to a lasting repair.  

Once this is repaired, peace and love will return to your neighborhood.

Cracked Wiring Insulation Hinders Engine Starts

Question 5

Two days ago without any warning my 2004 Nissan Altima started right away, but then it died.  It has a 2.4-liter engine.  When it starts it runs for a few seconds and stalls.  Pressing on the gas pedal does not help.

I removed the spark plugs and found they are wet with fuel. 

I went to a parts store to buy spark plugs.  An employee suggested that the trouble could be caused by a bad crankshaft or camshaft sensor so I installed new spark plugs and sensors.  This did not fix the trouble.

While I was replacing the spark plugs I found some cracked wiring to the ignition coils.  The insulation is cracked, but the wires inside are not.  A friend told me to replace the entire wiring harness.

Do you think this has anything to do with the problem?  If I cut the wires and repair them with waterproof connectors do you think this will fix the trouble?  Should I replace the harness?  P.D., email

Answer 5

It is doubtful you will be able to purchase a brand new harness.  They are scarce and expensive.  Also, replacing it may not fix the trouble.

Try to repair the wires.  It is the least expensive task.  It may or may not fix the trouble, but at least you won’t spend a ton of money.

Let’s hope it does the trick.  If not it is time to ask an experienced technician to troubleshoot the condition.

Check Engine Light Signals Misfire

Question 6

For the past year the check engine light has been intermittently flashing in my 2006 Subaru Forester.  When the light first began to flash I took the car to my local shop where a mechanic did some tests but he could not find anything wrong.  He suggested that I wait until the light turned on steadily. 

Presently, the light is not on steadily, but it is coming on more frequently.  Also, when the light turns on I feel the engine hesitate a little.  When the light turns off the engine runs fine, but I’m fearful the car will leave me stranded.  Now that the light turns on frequently do you think my mechanic will find the trouble?  Do know what causes the trouble?  S.W., email

Answer 6

Your description of the performance of the engine indicates it is misfiring.  If so, malfunction trouble codes should set in the engine control module.  Tests by an experienced technician should determine the cause.  It is possible a spark plug needs replacement.

Sometimes troubles such as this are caused by oil leaks at the spark plugs.  If this is the cause, it may be necessary to replace the valve covers on the engine.  This is not major surgery, but such a problem does raise repair cost.

 

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@drgizmo.ws. ® DR. GIZMO © 1989-2012