Vehicle Electrical/Electronics Troubleshooting Newsletter
Veejer Enterprises- Garland, Texas
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What would you do? Part 1
The Fix.....
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Welcome to all
those who have recently signed up for our
free email
newsletter!
What
Would You Do?
Part 1 - The Fix
A
repair shop was working with a sedan and the customer complaint was
the transmission would not shift. The make and model of the vehicle
and the type of repair shop, independent or dealership does not have
any particular bearing on this story and the fix. Let's consider this
a generic passenger car's transmission failing to shift problem.
A technician had
replaced the transmission with a rebuilt as he was told to do by the
shop foreman. As you might expect, the rebuilt transmission still did
not shift. The shop foreman insisted the transmission be replaced
again. The technician didn't agree and a discussion between the
technician and the shop foreman attracted the attention of a third
technician.
If you were that
third technician, what would you do? No, you can't walk away.
You are intrigued and want to help. So, what would you do?
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The
Fix
Thanks
to everyone that took the time to send me an email on what they would
do in the situation presented. Many "what I would do" strategies
were offered based on each individual technician's training and
experience. They covered numerous ways of approaching the situation.
No clear diagnostic method stands out above the rest. So let me tell
you what happened in this incident.
The third technician who overheard the discussion happened to have in
his possession a copy of the electrical flip-chart FIRST THINGS FIRST.
He had successfully used the flip-chart before and was confident in
taking a few moments to apply what he knew using the flip-chart to
perform 14 quick measurements.
When he performed Test Step 5, measuring the engine ground voltage
drop, he discovered a higher reading than normally found. Inspecting
the cable connection at the engine block revealed a less than tight
connection allowing the cable to move slightly side to side. He
applied a wrench to the mounting bolt and got a little tighter
connection. Then he tested the voltage drop and it was in the normal
range. The transmission shifted normally.
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You
may be wondering why the engine cranked and ran if the engine ground
had a higher than normal voltage drop? Glad you asked! The answer
lies in the operating principle of a solenoid which by its electrical
property opposes changes in electron current through it.
When in-rush electron current enters a solenoid, the rise in current
is opposed by the solenoid's inductive reactance which tends to
oppose the in-rush current. If the in-rush current is also inhibited
by a bad connection in the in-rush electron current path, what we
call a voltage drop, in-rush electron current may occur below the
level needed to activate the solenoid sufficiently to accomplish its
task. The result is a tranny with shift solenoids that can't shift
gears.
When the third tech identified the poor conductivity of the engine
ground cable, using FIRST
THINGS FIRST, the problem was identified as a
voltage drop and easily corrected. The in-rush electron current
could flow and operate the shift solenoids. It wasn't a tranny
problem afterall.
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Isn't
the starter solenoid a "solenoid too?" Why does a starter
solenoid operate when a shift solenoid in a tranny does not. Another
good question and I'm glad you asked. Let's say it this way. A
starter solenoid is a "lazy" solenoid and very slowwww
acting but eventually closes it contacts to complete the starter
circuit. You hear a dragging starter sound but the engine is turning
over so you don't give much thought to how long it took to close the
starter solenoid contacts. Solenoids in tyrannies have to act fast to
shift on time. They can't take their sweet time to energize like a
starter solenoid. If they do there is a no shift or late shift
problem.
In short, you can't overlook the primary electrical system that
provides in-rush electron current demands for shift solenoids. You
need to know what to do first.
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The
electrical flip-chart FIRST
THINGS FIRST focuses your attention on the
primary electrical system as the first thing to check and verify the
electrical system is ready to operate vehicle electrical-electronic
systems. The primary electrical system (battery, grounds and charging
system) is the area of the vehicle's electrical system most
technicians avoid because they are not confident in what to check -
how to check it - what should they get for a good DMM reading - and
what do I do if a DMM reading is too high or too low?
FIRST THINGS
FIRST shows you how to test the primary
electrical system in less than 5 minutes and find electrical problems
that are the real reason for the vehicle problem.
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Visit
our FIRST THINGS FIRST web page
for more info. There are two laminated versions available. A single
battery 12-14V test procedure in 14 steps for $79.00 and a dual
battery version in 18 test steps for $99.00. Order off the web site.
Shipping to US Zip codes is $7.00.
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End your newsletter with a kick — consider a postscript
to reinforce one of the key product or service benefits.
Sincerely,
Vince Fischelli
Veejer Enterprises
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