Northwest Herald Dr. Gizmo Column Dated July 6, 2012

07/06/2012

"Dr. Gizmo"
By Phil Arendt
 

Technician Can’t Put His Finger On Cause Of Symptoms 

Question 1

The check engine light is on in my 2001 Nissan Sentra.   I took the vehicle to a repair shop where a mechanic found trouble code PO171.  He said the engine is running too lean.  He did some tests that included testing the fuel pump and looked for air leaks in the engine, but did not find any troubles except the oxygen sensors were plugged in backwards.  He asked if anyone had worked on the car.  No one has worked on the vehicle except for routine services.  He reversed the electrical plugs, turned off the light and I drove home.  Everything was fine.

The next morning I was diving to work when I noticed that the car hesitated a little when accelerating until it warmed up.  Also, the check engine light turned back on.  I called the shop and the manager requested that I return for more tests

At the shop a mechanic found the same code had resurfaced.  He showed me a scope with all the things he checked.  Everything was within tolerance but he said that the he did not have any comparison values for a MAF sensor.   He does not know if there is a problem with the part.  He said that it might be the trouble but he does not want to replace it if he is not sure it is defective.  He said in his experience the MAF could cause symptoms similar to those I encounter.  I did not have the part installed.

Does what the mechanic says seem right to you?  Should I have him replace the part?  K.G., email

Answer 1

A faulty mass airflow sensor could cause symptoms such as you describe.  Since the part is fairly expensive, and cannot be returned to an auto parts store if it does not cure the trouble, consider these suggestions. 

Cleaning the part might be the cure.  Also, since your car is not disabled, maybe your technician could call you when a car like yours is in the shop for some other work.  If the MAF in that car is in good working order he could temporarily install it in your car to determine if the trouble is cured.  Of course, he will need the permission of the donor vehicle owner.  If this cures the trouble, installation of a new sensor will cure the condition.

Repairs Suggested, But No Guarantee
Question 2
The memory driver’s power seat and power adjustable steering wheel in my 2004 Nissan Maxima do not work.  I took the car to my local dealership where a technician checked a wiring harness and found it is okay.  He also temporarily installed a control unit and reset the system, but this was not the trouble.  Next, he attempted to operate the two motors under the seat and found they are cutting out.  After that he guessed that both motors need replacement, but he is not sure this will fix the trouble.  He wants to replace motors for $500 but if this is not the cause of the trouble, the parts cannot be taken out or returned.  Obviously, since a manager could not guarantee the parts would fix the trouble I did not have the work done.

The shop had the car for one week.  Now the seat is all the way back and tilted way back.  It’s very difficult for me to drive the car in that position.  Can you help?  D.W., Cary, IL.

Answer 2
In a week a couple of mechanically inclined thieves could dissemble a car and have the parts shipped all over the world.  Be this as it may, perhaps your shop needs more time.  One procedure a technician might consider is powering the seat motors independently from the system.  If the motors cut out, the test would confirm they are the cause of the trouble.   If they do not falter, something else in the system is causing the trouble such as a problem in the alleged good wiring harness.  And there is more than one harness routed in the seat.

Additionally, Nissan voluntarily recalled about 150,000 2004-2006 Maximas equipped with power lumbar supports because of a misrouted wire harness that was pinched.  Over time, vibration and seat movement could cause the wires to break and cause a fire.  While your car may or may not be covered by the voluntary recall it is possible a wire harness is pinched, is causing all of the trouble and needs replacement along with several other parts.

The 13 page bulletin your dealer may refer to is bulletin number NTB05-116a, campaign I.D. number PB011, National Highway Traffic Safety Administration number 05V-512.  If in fact the car is covered by the recall, repairs are free.  If not, it still would not hurt to investigate the wire harness addressed in the recall to rule it out as a possible fault.

Upset Over State Of Repairs
Question 3
I have a 2001 Chrysler Sebring with a 3.0 engine and 117,000 miles.  I’m very upset.  I have owned this car since it was new.  I take great care of it by following the maintenance schedule, but I change the oil more often.

The trouble is the check engine light is on.  I have taken the car to three different independent repair shops.  Each shop finds code 401.  Mechanics have replaced the exhaust gas recirculation valve, checked wiring, taken the engine apart to make sure ports are clear and they did many other checks.  When I pick up the car from a shop the check engine light is off.  After a few trips, the light turns back on.

When I have returned to any of the shops the same code pops up on test equipment.  One shop replaced the exhaust valve three times.  Another shop replaced an oxygen sensor even though it passed tests.

As I said I’m very upset.  Because the light is on, my car fails emission tests.  I’m told by the state testers that I better get the car fixed.  Can you help?  N.B., email

Answer 3
This is indeed a dilemma.  Diagnostic trouble code PO401 does indicate trouble in the exhaust gas recirculation system, valves, solenoids, wiring and ports.  There is a lot to check.  Even a fault in the powertrain control module can cause the light to turn on. 

If your shop has installed aftermarket parts consider having factory parts from a dealership parts department installed.  Sometimes this cures issues such as this.  Also, ask your favorite technician to clear all modules of learned processes.  This may do the trick.  During a test drive after the procedure the modules will go through a relearn process and all systems might return to normal function and the check engine light will remain off.

If original equipment parts do not resolve the issue, consider taking the car to a dealership.  It’s possible they may need to reprogram the powertrain control module or replace it.

Simple Procedure Might Cure Trouble
Question 4
I have a 2008 Honda Accord with a 3.5-liter engine and 35,000 miles.  The trouble is that intermittently the engine stalls.  When this happens there are no warning lights including the check engine light.  The engine usually stalls at slow speeds in parking lots or when coming to a slow stop.  Sometimes it stalls when the transmission is in drive, the engine is idling and I take my foot off the brake to accelerate.  I just never know when it will stall. 

I’ve taken the car to an independent shop and a dealership shop.  Both shops did tests but did not find any codes in the computer.  Both shops checked wiring and sensors but they determined the car is operating within specifications.  Both shops test drove the vehicle, but the engine did not stall for them.  Both shops reset the computer.  One shop suggested the trouble might be in the throttle actuator.  The other shop said the throttle actuator or mass air sensor could be the trouble.  Neither shop guaranteed that replacing the parts would cure the problem. 

What do you suggest?  H.G., email

Answer 4
Fill the gas tank.  Drive as far as a tank of gas will allow.  Purchase a new car.  Drive back.  All kidding aside, there may be a simple solution.  Often when an engine stalls and everything checks okay, cleaning the throttle body cures the condition.  This is a simple procedure.  This might resolve the condition, frustration and inconvenience.

If cleaning does the trick, the engine may not stall at all during a dozen coast to coast trips or until the throttle body requires additional cleaning.

Extensive Repair Might Cost Servicing Shop A Few Bucks

Question 5
Eight months ago, I purchased a 2007 Toyota Camry with a 3.5-liter engine.  It had 77,000 miles at the time of purchase.  Now it has 85,000 miles.

Two weeks ago the heater core sprung a leak which caused antifreeze to leak on the floor.  A local shop replaced the leaky part, replaced the carpeting and all was well except that every once in a while since the repair all of the warning lights in the dash blink.

I returned to the repair shop where a mechanic replaced the alternator and a relay.  This did not cure the trouble.  Now they are telling me there is nothing more they can do.  They suggest that I take the car to a dealership for more work.

I think something happened during the heater repair that is causing the trouble and they should fix it.  What do you think?  S.P., email

Answer 5
As you probably have learned replacing the heater core is a major operation.  Just about everything you see on the dash is disassembled including the center console, steering wheel, dash pad, air bags, radio and heater and instrument cluster.  Besides the steering wheel, one of the first units to remove and one of the last to be reinstalled in the dash is the instrument cluster.  Since the warning lights are blinking I suspect there is a loose connection behind the cluster.

Ask your shop manager to consider checking the connections behind the cluster.  If he balks, suggest that if a dealer technician finds loose connections at the rear of the cluster he will need to reimburse you for the repair.  He might consider investing a little more time on the condition before shuffling you to a dealer.  Better yet, ask him to take the car to a dealer.  Some reputable repair shops have good relations with dealer shops and his shop might be in the position to ask a dealer for some help.   If not, and the trouble indeed is caused by loose connections save your dealer repair receipts and present copies to the owner of the repair shop for reimbursement.  Also, if indeed a loose connection is the cause, you might ask for reimbursement for the alternator and relay.

Technician Suspected Of Negligence

Question 6
Recently, I was driving along in my 2001 Ford Focus when I heard a loud bang and the engine stalled.  I had the car towed to my repair shop.  They have been servicing the car for about four years.  A mechanic found that the timing belt broke.  Within a couple of days he finished the repairs.

After the repair, I noticed that the engine is not running as smooth as before the incident.  Other than this, the engine runs fine.  I returned to the shop.  A mechanic determined the intake manifold has cracks.  He says it’s plastic.  To fix the trouble it must be replaced. 

My car has 140,000 miles and a 2.0-liter engine.  I have owned it since it was new.  I have taken good care of it by following the owner’s manual schedule.  How can this part crack?  Does it need removal to replace the timing belt?  Could the mechanic have cracked it?  D.R., email

Answer 6

This issue is unfortunate.  First, your technician did not have to remove the manifold to replace the timing belt.  Additionally, the cracks in the manifold must be minor or fuel trims would run beyond specifications and cause the check engine light to illuminate.  If the cracks were severe, it’s likely the issue would have been found during a test drive after the repair.  Additionally, the check engine light would have illuminated for you once you received the car. 

Plastic intake manifolds are commonly used on engines.  They are made from thermoplastics that are much more robust than plastic storage containers.  Unfortunately, the plastic is not as robust as aluminum manifolds that also are commonly used in the construction of engines.  Sometimes plastic manifolds crack.  They fail for a variety of reasons including expansion and contraction at mating surfaces.

Sometimes under the stresses of a backfire they fail.  This might be what caused the manifold on your engine to crack.  When the timing belt broke the engine suddenly went out of time.  This can cause an internal explosion, commonly known as a backfire.  The pressure from an explosive backfire can escape through the exhaust system or intake manifold.  I suspect the pressure of a backfire exceeded the design pressure specifications of the manifold causing cracks in the plastic.  Cracks cause leaks that cause an engine to run rough.  The fix is to replace the manifold.

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.  07/06/2012 ® DR. GIZMO © 1989-2012