14 GEARS April 2009

Welcome 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.

Performance CodesJust about every manufacturer has

solenoid performance codes. A solenoid performance code might as well be a ratio code; it means the solenoid is working properly electrically, accord-ing to the computer.

What isn’t working properly are the results of the solenoid’s operation; the gear it’s responsible for is slipping or missing. The computer identifies this performance problem through the speed sensors, so the condition may or may not be accompanied by gear ratio error codes.

An important first step when com-

ing across any solenoid code is to look up the code definition in your repair manuals or software. The criteria the computer looks for when setting the code will be listed in the definition or diagnostic tree.

If the code is ratio-related, you only need to check the solenoid for mechanical operation: Resistance or other electrical tests aren’t necessary if there aren’t any electrical codes pres-ent. The vehicle’s computer has a built-in ammeter that constantly checks the solenoid during vehicle operation, so it’ll set an electrical code if it detects an electrical problem in the solenoid

circuit. How do you test a solenoid mechan-

ically? Depending on the solenoid, you may have to use special testing equip-ment that checks solenoid flow using air or fluid. Remember, you’re check-ing the solenoid’s mechanical opera-tion. On other solenoids, applying regu-lated air through the working end of the solenoid with a rubber tipped blow gun will work (figure 1).

When checking an on/off solenoid, energizing the solenoid will either open or close the valve inside, and either stop flow or let it come through. You’re just looking for a change of state.

PLAYING WITH FIRE

by Jon Rodriguez

Playing with Fire is

Because of a Solenoid Code

Figure 1

14jonrodrgz409.indd 14 3/17/09 1:54:51 PM

16 GEARS April 2009

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 2

Figure 3

Figure 4

Playing with Fire is Changing a Solenoid Because of a Solenoid Code

16 GEARS April 2009

GEARS April 2009 17

continue the diagnoses as you would for an internal problem. (Check band adjustments, air check individual components, check fluid and sump condition, etc.)

Electrical CodesThe computer will set a solenoid

electrical code if it measures incor-rect amperage in the circuit, or sees an improper inductive spike when operat-ing the solenoid. The amperage that a solenoid draws is based on the amount of voltage being supplied to the sole-noid, divided by the amount of resis-tance in the solenoid. That’s Ohm’s 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.

Voltage SupplyStart by logging on to www.atra.

com and print out a copy of bulletin #1244. The bulletin pertains to solenoid electrical codes in GM Rear Wheel Drive Vehicles being caused by Ignition switch issues.

Sometimes the computer will set every code for each solenoid that’s powered by the E wire; other times it will only set one code. The computer sometimes will set one electrical code and then go into limp and not monitor the rest of the solenoids. Other times, you’ll get lucky and have every electri-

cal solenoid code except for the EPC and Pressure Switch Manifold, because they’re on their own circuits. When all the codes are set at the same time, it’s safe to jump straight to a power supply diagnosis.

You’ll notice several areas circled on the diagrams in the bulletin. These are points for testing. For these tests you’ll need a quality multimeter; not a test light. A test light won’t work because a drop of as little as one volt can cause the code or codes to set. A test light can only tell you if power is present; not whether it’s low.

18 GEARS April 2009

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 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 positions: ACC, RUN, and START — and work it back and forth.

A faulty ignition switch will cause the voltage readings to fluctuate as the corroded contacts in the switch make and break connection. A good switch will have less than 0.10 volts fluctuation during this test.

Another quick test to see if the power supply is causing the codes is to connect a fused jumper wire from the positive battery terminal to the E wire, as close to the transmission connector as possible (figure 5). This will bypass the rest of the circuit; if the codes don’t return with the jumper con-nected, you know it’s because of a problem in the power feed circuit.

Keep in mind that you won’t be able to turn the engine off until you disconnect the jumper wire from the E wire.

If connecting the jumper wire does not eliminate the code(s), chances are you’re dealing with a bad solenoid,

a circuit problem between the computer and the solenoid, or a bad computer.

A quick test to eliminate the computer is to perform a solenoid bypass test: connecting a known-good solenoid with the same resistance as the solenoid in question, and wiring it directly to the computer (figure 6).

The computer has no way of knowing the solenoid is wired in at the computer, or if the solenoid even belongs to that transmission. It just has to be the same resistance and have a good power supply. If the code returns, the problem is either in the short amount of wiring between the computer and the test solenoid, or the computer itself.

Even though we focused on GMs for this article, the procedures and electrical theory we discussed can be used on several vehicles that comes into your shop, and will help you conquer the toughest solenoid electrical problems that come your way.

Figure 5

Figure 6

Playing with Fire is Changing a Solenoid Because of a Solenoid Code

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