This article explains the difference between solenoid performance codes and circuit or electrical codes.

1. PLAYING WITH FIRE
Playing with Fire is
by Jon Rodriguez
Because of a
Solenoid Code
W
elcome to another edition of
Playing with Fire. Instead
of discussing interchange,
we’re going to go over solenoid code
diagnostics.
It’s an all-to-common occurrence
for a solenoid to be replaced because
the code definition contains the word
“solenoid”… and then have the code
come back, because the root cause of
the failure wasn’t the solenoid at all.
We’re going to go over the differ-
ences between performance codes and
electrical codes, and see how to diag-
nose them properly before replacing a
solenoid.
Figure 1
Performance Codes ing across any solenoid code is to look circuit.
Just about every manufacturer has up the code definition in your repair How do you test a solenoid mechan-
solenoid performance codes. A solenoid manuals or software. The criteria the ically? Depending on the solenoid, you
performance code might as well be computer looks for when setting the may have to use special testing equip-
a ratio code; it means the solenoid is code will be listed in the definition or ment that checks solenoid flow using
working properly electrically, accord- diagnostic tree. air or fluid. Remember, you’re check-
ing to the computer. If the code is ratio-related, you ing the solenoid’s mechanical opera-
What isn’t working properly are only need to check the solenoid for tion. On other solenoids, applying regu-
the results of the solenoid’s operation; mechanical operation: Resistance or lated air through the working end of the
the gear it’s responsible for is slipping other electrical tests aren’t necessary if solenoid with a rubber tipped blow gun
or missing. The computer identifies there aren’t any electrical codes pres- will work (figure 1).
this performance problem through the ent. The vehicle’s computer has a built- When checking an on/off solenoid,
speed sensors, so the condition may or in ammeter that constantly checks the energizing the solenoid will either open
may not be accompanied by gear ratio solenoid during vehicle operation, so or close the valve inside, and either stop
error codes. it’ll set an electrical code if it detects flow or let it come through. You’re just
An important first step when com- an electrical problem in the solenoid looking for a change of state.
14 GEARS April 2009

3. Playing with Fire is Changing a Solenoid Because of a Solenoid Code
Figure 2
Figure 3
Pulse Width Modulated
(PWM) solenoids require spe-
cial equipment to provide the
duty-cycled control signal and
measure the solenoid’s flow char-
acteristics.
What it comes down to is
this: Solenoid performance codes
are only rarely caused by a faulty
solenoid. More often they’re
caused by another part of the sys-
tem; replacing the solenoid won’t
help. So how can you determine
what’s causing the code?
The first step when
diagnosing a performance code is
to test drive the car and see what
gear seems to missing or slipping.
A clutch-and-band application
chart will help guide you to the
component that’s responsible
for the missing or slipping gear.
After you have an idea of what
component is causing the slip, Figure 4
16 GEARS April 2009

4. continue the diagnoses as you would cal solenoid code except for the EPC
for an internal problem. (Check band
Voltage Supply and Pressure Switch Manifold, because
adjustments, air check individual Start by logging on to www.atra. they’re on their own circuits. When all
components, check fluid and sump com and print out a copy of bulletin the codes are set at the same time, it’s
condition, etc.) #1244. The bulletin pertains to solenoid safe to jump straight to a power supply
electrical codes in GM Rear Wheel diagnosis.
Electrical Codes Drive Vehicles being caused by Ignition You’ll notice several areas circled
The computer will set a solenoid switch issues. on the diagrams in the bulletin. These
electrical code if it measures incor- Sometimes the computer will set are points for testing. For these tests
rect amperage in the circuit, or sees an every code for each solenoid that’s you’ll need a quality multimeter; not
improper inductive spike when operat- powered by the E wire; other times it a test light. A test light won’t work
ing the solenoid. The amperage that a will only set one code. The computer because a drop of as little as one volt
solenoid draws is based on the amount sometimes will set one electrical code can cause the code or codes to set. A
of voltage being supplied to the sole- and then go into limp and not monitor test light can only tell you if power is
noid, divided by the amount of resis- the rest of the solenoids. Other times, present; not whether it’s low.
tance in the solenoid. That’s Ohm’s you’ll get lucky and have every electri-
Law (figure 2).
In an ideal situation, the code
would indicate an existing problem
(hard code); checking the resistance
with your multimeter would reveal the
problem instantly, and changing the
solenoid would eliminate the code.
Those are the easy ones. The harder
ones are the codes that come and go,
or aren’t caused by the solenoid at all.
We’re going to go over those types of
problems.
In most applications, all three
domestic manufacturers use a system
that provides power to all of the sole-
noids from a common source. The com-
puter grounds the solenoids to operate
them, and monitors amperage from the
ground side of the circuit. Which leaves
two things that can go wrong:
1. A problem with the voltage supply
to the solenoids (ignition switch,
fuse, battery, etc.)
2. An open or shorted signal wire
from the computer to the solenoid.
We’re going to refer to ATRA
Technical Bulletin #1244. The bulletin
provides all of the wiring schematics
for Chevrolet and GMC trucks with a
4L60E, from 1993 to 2006, and high-
lights the points of interest when deal-
ing with power supply issues.
Rear wheel drive GM pickups are
a good vehicle to use for going over
these diagnoses because of the number
of switch issues that can cause solenoid
codes. Keep in mind that Ford and
Chrysler have a slightly different way
of supplying power, but you can use
the same approach to diagnose those
vehicles.
GEARS April 2009 17

5. Playing with Fire is Changing a Solenoid Because of a Solenoid Code
First start with the battery. With the key on,
engine off (KOEO), measure and record battery
voltage; that’s your system voltage value. A new
battery should provide a no-load voltage of 12.6
volts. Use the chart in figure 3 to determine the
condition of the battery. If the battery is outside
limits, substitute or replace the battery with a
good one.
Now that you have your system voltage
value, backprobe the transmission harness con-
nector and measure the voltage supply. If it’s
below system voltage, work your way back to
the voltage source until your voltage rises to
within 0.1 volts of the system voltage.
The resistance is hiding between this last
measurement and the previous one. If it’s at a
connector, it’s most likely inside where the cop-
per wire is crimped to the terminal. You may see
green or white corrosion on the copper; that’s
all it takes to throw the system off. Clean and Figure 5
retest; in some cases you may have to replace
the connector.
On GMs, it’s common for the ignition
switch to wear and add resistance to the circuit.
Here’s a shortcut for testing the ignition switch:
1. Remove the fuse that provides power to the
transmission. In GM trucks, it’s located in
the fuse compartment on the driver’s side
dash (figure 4).
2. Set your multimeter to DC volts.
3. With KOEO, connect the positive meter
lead to the fuse clip that has voltage with the
fuse removed.
4. Connect the negative meter lead to the
negative battery terminal.
5. Set the parking brake to keep the car from
rolling.
6. Place the transmission selector lever into
reverse so the engine won’t start when you
turn the key.
7. Slowly move the ignition switch through its Figure 6
positions: ACC, RUN, and START — and
work it back and forth. a circuit problem between the computer and the solenoid,
or a bad computer.
A faulty ignition switch will cause the voltage readings A quick test to eliminate the computer is to perform a
to fluctuate as the corroded contacts in the switch make and solenoid bypass test: connecting a known-good solenoid with
break connection. A good switch will have less than 0.10 volts the same resistance as the solenoid in question, and wiring it
fluctuation during this test. directly to the computer (figure 6).
Another quick test to see if the power supply is causing The computer has no way of knowing the solenoid is
the codes is to connect a fused jumper wire from the positive wired in at the computer, or if the solenoid even belongs to
battery terminal to the E wire, as close to the transmission that transmission. It just has to be the same resistance and
connector as possible (figure 5). This will bypass the rest have a good power supply. If the code returns, the problem is
of the circuit; if the codes don’t return with the jumper con- either in the short amount of wiring between the computer and
nected, you know it’s because of a problem in the power feed the test solenoid, or the computer itself.
circuit. Even though we focused on GMs for this article, the
Keep in mind that you won’t be able to turn the engine off procedures and electrical theory we discussed can be used on
until you disconnect the jumper wire from the E wire. several vehicles that comes into your shop, and will help you
If connecting the jumper wire does not eliminate the conquer the toughest solenoid electrical problems that come
code(s), chances are you’re dealing with a bad solenoid, your way.
18 GEARS April 2009

6. As a dedicated transmission professional
Rick Basta, owner of Transmission Kings,
knows the secret to a successful shop is
dependable performance and satisfied
customers. That’s why he rebuilds with
TransTec®.
No surprises. Buy a TransTec® kit and you
“MY GUYS
can bet the bank that all the parts required
for the job are there and that they all fit. It’s ALWAYS REQUEST
no accident; our engineering department,
product development and technical staffs,
plus a proven QA system, combine to give
TRANSTEC®.”
you the assurance you can’t get anywhere Rick Basta,
else. Owner of Transmission Kings
Manufactured to meet the strictest OE Cleveland, OH
standards, TransTec® kits contribute to a
faster rebuild with virtually no comebacks.
And detailed technical inserts reinforce what
the technicians learn at various seminars.
These are just a few reasons why transmis-
sion rebuilders request “the kit in the gold
and black bag”.
TransTec® kits are produced by Freuden-
berg-NOK™, the American partnership with
more than $6 billion in resources. Yet it is
the close, personal support that impresses
transmission shops like Rick’s.
TransTec® makes it easy.
A Division of Freudenberg-NOK