"Dr. Gizmo"
By Phil Arendt
New Automotive Technology
Needs Constant Electrical Power
Question 1
Recently, I read
your response in my local paper regarding battery disconnect switches. I’ve been using them on older vehicles for over 30 years with
outstanding battery life results. I own five vehicles that
are located in three different states. Some sit for six
months or more in unheated space and always start without difficulty or
incident. The battery condition is monitored and fully charged prior
to turning the switch off. When charging, if battery
voltage goes out of profile I replace it. I’ve been using Wal-Mart
Maxx batteries with very good results.
Our newest vehicle is a 1998 Suburban with a 350
gas engine, 148,000 miles, and dual battery installation with dual
disconnects. It's always parked outside in Minnesota winters.
Recently, I’ve been shopping for a new 2013 gasoline powered Chevrolet
Suburban. Dealer personnel tell me a
battery disconnect switch is not recommended because of the computers. They recommend using an
onboard trickle charger. However, a plug may not be not be
possible in all the places the new vehicle might be stored or parked,
which could involve several idle months.
Also, provided by the selling dealer was some jargon about a
built-in "battery saver" circuit which automatically reduces the
battery drain to "non-essential" computer circuits when the
battery runs low. It sounds to me
if there is non-essential drain, that's even more reason to disconnect the
battery over long periods. The new Suburbans have a space for a
second battery so I plan to go that route in any event.
What is your opinion about installing battery disconnects on new
vehicles? J.J., West Saint Paul, Minn.
Answer 1
Don’t do it. Your dealer is
correct. Your new Suburban has technology
light years ahead of your 1998 vehicle with many computer modules that have a
feature known as “keep alive memory”. They
need a trickle of electrical power to maintain memory. Even a battery that does not hold enough
power to start an engine and is considered failed usually has enough power to
maintain computer memory unless it completely failed due to problems such as an
internal short. If a computer module completely
loses power the memory fails. If your
vehicle suffers from computer dementia, this could send your vehicle to a dealer
to have modules reprogrammed or even replaced.
To avoid this, consider a battery maintainer instead of battery
disconnect switches. The switches will
completely shut down power to modules. Since
you may not have household current available to power a 110 volt battery
maintainer, consider using a solar powered unit with circuitry that monitors
the state-of-charge so that it only charges when needed. The cost of a solar powered unit is around
$100. A household current battery maintainer
costs around $40.
After Repair, Engine Stalls
Question 2Last week I had to take my 2002 GMC Yukon in for repair because the check engine light turned on. A mechanic found a leak in a seal on the intake manifold. He repaired the trouble and I drove home. Everything was fine. I was at home about a half an hour and had to run an errand. I started the engine and then it died. I repeated the process several times. I called my repair shop. They sent a tow truck and hauled the vehicle away. A little while later they called and said that their mechanic started the vehicle and it was fine. He drove to my home and we went for an extended ride after a while I dropped him off at the shop. I drove home and my Yukon has been running fine ever since.
I’m a little worried the vehicle will leave me stranded. Was this just a freak incident or is there
something going on I should be worried about?
J.H., email
Answer 2
Since the vehicle is operating normally it appears to be a freak
incident. You know how your vehicle
operates better than anyone. If there
does not appear to be any unusual conditions, chalk this one up to
gremlins.
More than likely a computer module lost its memory. As a safety precaution technicians disconnect
the battery especially during major repairs.
Often technicians install a device to power modules while the battery is
disconnected so computers do not lose memory.
It’s possible your technician forgot or the power supply was
inadvertently disconnected.
At home, it is likely a module was a little fuzzy and it caused
the engine to stall. Now that it has a
constant power supply it has relearned your driving habits, calibrations and algorithms
and all is well until the next time something else fails which might be years
from now.
Engine Runs Worse After Repair
Question 3My 2006 Honda Pilot EX with a 3.5-liter engine stalls and the check engine light is on. I went to an auto supply store to have the computer checked. The parts guy found code PO507. He says there are many possible causes for this code. He suggested that I take the car to a shop.
I took the vehicle to my local repair shop where a mechanic
replaced the intake manifold gasket.
After the repair I drove home but the idle was erratic. I returned to the repair shop the next day
and left the vehicle. They had it all
day but could not find anything wrong. I
picked up the vehicle because I need it.
The idle problem continues.
It did not have this problem before the repair. What do you think is wrong? M.W., email
Answer 3
Return to the repair shop.
It is obvious there is something causing the trouble. Suspicion points toward a leak somewhere in
the intake manifold. Perhaps the gasket
slipped when the technician installed the manifold. Perhaps the gasket is defective. To find out the cause he likely will remove
the intake but you will need to give ample time for him to do his investigative
work.
Trust Your Technician
Question 4My 2003 Ford Windstar with a 3.8 engine stalled while driving. After it stalled the engine cranked but would not start. I had it towed to dealer. They have been servicing the vehicle since it was new.
A technician has performed many tests but has not found the exact
cause of the trouble. He has checked the
fuel pump and computer for trouble codes.
He has tested the ignition coil, crank shaft sensor and many other
parts. He also tested the antitheft
system but no luck. He can’t find the
trouble. He is uncertain but thinks that
if he replaces the engine control module the problem will be cured.
The engine computer is expensive.
There is no guarantee this will fix the trouble. If he installs the part I’m stuck with it
even if it does not fix the trouble. Do
you think a new engine computer module will cure the problem? M.D.P., email
Answer 4
I can understand your concern.
Also, an experienced technician certainly does not want to install a
part if he is not confident it will fix a problem. Additionally, your dealer has the most
up-to-date diagnostic equipment and factory trained technicians. More than likely he has performed a multitude
of tests and with a reasonable degree of automotive certainty he or she has
ascertained that the engine control module has a fault and is the cause of this
condition. Certainly the part is
expensive but it is the main control of the powertrain. Sometimes when this part has an internal
fault it is impossible for diagnostic equipment to communicate with it in a way
that makes sense. If it scrambles
communications a technician and the diagnostic equipment just can’t pinpoint
the trouble other than to conclude that there is trouble in the unit.
At this point I’m sure he has exhausted all other possible
causes. It is time to replace it.
A/C Damaged In Collision Does Not Work After Numerous Repairs
Question 5I’m upset. I own a 2006 Chevrolet Impala LTZ that I’ve owned since new. It has a 3.9-liter engine and 51,000 miles. Last summer the front-end was damaged when a person made a left hand turn in front me and I broadsided him. The damage was to the fenders, hood, front bumper, headlights, grille, radiator and air conditioning parts. All the damage was repaired but since then the air conditioner has not worked despite several attempts to repair it. The air conditioner worked fine before the accident. I need to have this repaired before summer arrives.
The shop that is doing the work has replaced the compressor, expansion
valve, cooling fans, relays, condenser, dryer and they flushed the system. The compressor has been replaced three
times. Despite all of this work sometimes
the compressor does not turn on when I select air conditioning on the
controls. Of course during the winter it
is difficult to determine if it turns on but last fall after the third
compressor was installed it did not work properly. My shop suggested I come back this spring to
have them look into the trouble again.
Do you have any suggestions?
L.R., email
Answer 5
To cure this, turn on the 2-60 system. Open two windows at 60 mph. All kidding aside, your shop has done a lot work but it is obvious the cure eludes them. A check of all the wiring is in order not just at the front-end. There may be a loose ground connection or pin in a plug. Maybe a wire sustained damage that may be hidden under insulation. It’s also possible something is trapped in the system that needs flushing. Flushing individual components such as the evaporator and refrigerant lines might be the cure. It’s also possible the jolt of the collision has affected the control module in the dash.
Since the system is complicated a technician needs to monitor
system pressures, sensors and controls while the system cycles on its own. A technician can manually cycle the system
with test equipment to determine function of different parts in the system but it
is very important to allow system to function on its own. In doing so, he can monitor system pressure
and electronics as all the parts work to cool the cabin. When pressure abnormally drops or rises or an
electrical device falters he will be able to determine the cause of the
trouble. More than likely the trouble is
not the compressor.
Wiring Trouble Disables Fuel Pump
Question 6
I own a 1996 Chevrolet Monte Carlo LS with 158,000 miles. The body and interior are in like new condition. I replaced the engine and transmission. They have 22,000 miles on them.
About 300 miles ago, trouble developed. The problem is the fuel pump quits and I’m
temporarily stranded. The first time it
quit I found that it developed plenty of pressure and volume but once in a
while it stopped. When I checked for
electrical power to the pump it had power and it was working. I thought there was an internal problem so I
replaced it. The next time the engine
stalled I checked the pump and there was no power to it. I replaced the relay even though it seemed
fine. I was confident the trouble was
repaired but the engine stalled again.
When I was able to check the pump there was electrical power and the
engine started and ran fine.
The trouble is intermittent.
I know something is going on that stops power supplied to the fuel pump.
I know that the engine control module
has something to do with sending power to it.
I’ve owned this car since it was new. It’s my baby.
Do you think replacing the engine module will fix the trouble? G.R., email
Answer 6
Your baby will soon be cruising the highways. There is much more to check before you replace the engine control module. Certainly the ECM sends a signal to the fuel pump relay. Closing the relay turns on the pump. You already know that for some reason power is interrupted. This might be caused by a loose or corroded pin in a plug. Perhaps there is a loose or corroded ground connection. It is possible a wire is broken, chaffed or loose somewhere in the circuit. Additionally, it is possible there is trouble in the antitheft system that disables the pump.
Since it is likely you do not have the proper diagnostic equipment
to test modules a little ingenuity might find the trouble. Consider making a test circuit with a light
that you can monitor inside the vehicle.
Using a schematic identify the wiring from the ECM to the relay. More than likely it is a ground circuit so
you will need to check for a proper ground circuit. Install your tester in the circuit. If the light remains illuminated when the
pump stops you will know the circuit between the ECM and relay is okay. Continue through the circuit until you find
the area of the fault. Who knows you
might find the wiring in the passenger compartment has a fault. If all the wiring checks out fine, it’s time
to take the vehicle to a shop to have the antitheft system and control modules
tested but I have a strong hunch the trouble is in the wiring.
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 03/11/2013 ® DR. GIZMO © 1989-Present
