Electrical Testing in the Operating Room; Part 6

DOCTORDOCTOR It hurts when I shift! by Randall Schroeder Electrical Testing in the Operating Room; Part 6 IIn the operating room, doctors are faced with precise test procedures that are challenging and need to be done correctly to prevent damage. If done incorrectly, these procedures not only waste time, but can also be costly in unnecessary parts replacement or circuit damage. So far, here is what we have covered in this series: Part 1 The importance of power and grounds, and how to check them properly (GEARS January/February 2002). Part 2 Testing temperature sensors and throttle position sensors; starting tests at the sensor and confirming them at the computer (GEARS March 2002). Part 3 Park/neutral switches and accelerator switches. Along with the park/neutral switches, we led into range selectors, which are a very important input, not only for line rise in electronicallycontrolled transmissions, but also how they tie in with the range the driver has selected (GEARS October 2002). Part 4 Speed sensing devices and pressure switches. We covered the similarities in the different speed sensors and how to check them. We looked at pressure switches and their uses, and learned that the name switch is exactly what the name implies: an onoff device, like a light switch (GEARS JanuaryFebruary 2003). Part 5 Shift solenoids; how the computer takes the inputs we covered earlier, and uses that information to control the shift solenoids to create an upshift or downshift at perfect speeds (well, in theory). Basically, shift solenoids have taken the place of governor pressure to move the shift valves, when valves are used; and in some instances Figure 1 taken the place of the valves altogether (GEARS April 2003). In this issue of Doctor, Doctor, we re going to look at line pressure solenoids, governor solenoids (42RE/47RE), and modulating shift solenoids (32 4L60E). When you understand how these solenoids work, it is easier to see how they affect shift feel and timing. The theory is simple: Solenoids can be used to alter shift feel (accumulator solenoid), control governor pressure (shift timing), and most commonly, take the place of the TV oil (throttle valve or modulator) that was used for line rise (pressure regulation). This is called managed oil flow into a circuit. Figure 2 78 GEARS September 2003

The computer uses a solenoid to achieve this managed oil flow by pulsing the solenoid on and off (duty cycle) to regulate a supplied oil pressure. This pressure either moves a shift valve or sends oil directly into the pressure control valve boost circuit. This is similar to the valve control in nonelectronic transmissions, but uses electrical signals to achieve the same results. Common names for these solenoids are: EPC Electronic Pressure Control (line pressure) Force Motor Variable pressure control (line pressure) Pressure Control Solenoid Line pressure Modulated TCC Solenoid Torque converter 32 Shift Solenoid Modulated downshift Solenoid Block 41TE/42LE Governor Pressure Solenoid 42RE/47RE Shift Solenoids Many imports and Chryslers Line Pressure Control Solenoids Line pressure solenoids have taken the place of the TV or vacuum modulator used on earlier transmissions to boost pressure. As line pressure (regulated through a valve or not) goes through the solenoid, it sends a regulated amount of pressure to act on the boost valve through its sleeve in the regulator valve lineup. This pressure supplies the extra force needed to move the boost valve against the regulator valve, causing line rise (figure 1). If everything was perfect, the oil pressure from the solenoid at idle would be 0 PSI. Since things aren t always perfect, there will usually be about 5 to 10 PSI feeding the boost circuit at idle, and the pressure goes up from there. The oil from the solenoid (called conventional TV oil pressure) is directed to the pressure boost valve (figure 2). This moves the PR valve toward boost pressure. Line pressure boosts when the PR valve moves down toward the bottom of its bore. IMPORTANT: If there s a problem with balance oil on the PR valve, line pressure will be high, even if the solenoid is doing its job correctly. Testing these solenoids can be Expertise to help steer you in the right direction. Throughout the years, Fred Burkhart and Brent Funk have built up the RoadMaster name with the knowledge and skill that only comes through industry experience. But you can never have too many experts on the job and that s why we are pleased to welcome Bill Anthony as Director of R&D and Jeff CollinsworthSales Manager, into our family. With decades of industry experience among us, we know this decision will give us the advantage and expertise to keep providing you with the most dependable parts on the market. Having the parts you need is essential. Knowing what you need is the difference. RoadMaster offers a complete line of parts that deliver the quality and performance you demand. And now we ve added over 50 new solenoid, actuator, and sensor part numbers to our growing line. So when you need reliable parts backed by the experts, remember RoadMaster. Contact us today for prices and a distributor near you. CORPORATE: 1016 Dixie Highway, Suite B, Rossford, OH 43460 Phone: 419.662.8924 Fax: 419.662.8925 fburkttxe@inetmail.att.net DISTRIBUTION CENTER: 416 Justice St., Fremont, OH 43420 Phone: 419.333.1200 Fax: 419.333.1202 ttxeinc@nwonline.net GEARS September 2003 79

Electrical Testing in the Operating Room; Part 6 tricky, but they all work basically the same way. GM varies the current flow to the solenoid, from 1.1 amps at normal operation, down to 0.0 amps for maximum pressure. Since the system controls pressure by varying current flow through the solenoid, the best way to monitor system operation is with an ammeter in series with the solenoid (figure 3). Scan tools will usually provide the amperage signal that the computer provides. This solenoid operates from a duty cycle signal in the positive circuit of about 292.5 Hz (figure 4). At minimum throttle (idle), the signal ontime increases, so the current flow approaches 1.1 amps. This keeps the armature forced back against the plunger, compressing the spring, and holding the valve plunger up. In this condition, there s no filtered actuator feed oil flow (figure 5). As the load increases, current decreases, which lowers the field force pulling on the spring. At full throttle, current flow drops to 0.0 amps, and the plunger settles to the bottom of the solenoid. This allows maximum actuator oil flow, which creates maximum pressure (figure 6). Sound simple? Once you understand it, it really is. Let s look at the Ford VPS (Variable Pressure Solenoid). Many people refer to this as the EPC solenoid, or Electronic Pressure Control solenoid. Ford regulates the ground side of the EPC to increase current flow through the solenoid, and raise system pressure. At idle, this circuit should have 7 volts on the ground side, and it should drop to almost zero volts at hard throttle. This is how you may have seen it on your scan tools. It s often easier to test these solenoids by connecting your voltmeter s positive lead to the solenoid positive wire, and the negative lead to the solenoid negative wire (figures 7A,7B). This will provide a different measurement than the one you see on your scan tool; in fact, you ll see the opposite reading altogether. Instead of voltage rising with line pressure, the voltage drops as line pressure increases. With this setup, voltage is usually around 5 volts at idle, and drops to almost 0.0 volts at hard Force Motor amps Figure 3 throttle. This is no different than unplugging the transmission to create maximum pressure. IMPORTANT: While we use 12 volts to describe system voltage in this discussion, don t forget that system voltage will usually be somewhat higher; about 14 volts or so with the engine running. Which means the idle voltage may be a bit higher than discussed; maybe 6 volts or more. Always compare the solenoid feed voltage with the system voltage. Any substantial difference indicates unwanted resistance in the circuit. The working voltage for the pressure control solenoid should be around 5V for 0 PSI boost pressure in the TV circuit. When the working voltage drops to 0 volts, TV pressure should boost Figure 4 Figure 6 PRESSURE CONTROL SOLENOID Figure 5 EPC Voltage Decreases from 5v to 0v DC EPC Voltage Increases from 6v to 13v DC Ignition Trans. relay Gov. Solenoid Figure 7A Figure 7B Figure 8 80 GEARS September 2003

Electrical Testing in the Operating Room; Part 6 upwards of 90 PSI (EPC pressure boost pressure can go as high as 120 PSI). This would be the same as if you d unplugged the solenoid. If the vehicle you re working seems to be slipping, install a pressure gauge and disconnect the power to the solenoids; the system should jump to maximum line pressure. If the line pressure doesn t rise to maximum, look for a leaking solenoid or internal transmission problems. Disconnecting the solenoid is a simple check to make sure the transmission line rise is working properly. To help with diagnoses, test the signals on every vehicle that come into your shop, and keep a chart for future use. Record keyoff voltages, keyon voltages, and enginerunning voltages. Having these voltage measurements available makes diagnoses a snap if you suspect you re dealing with an electrical failure. Governor Solenoid The governor solenoid in the Chrysler 4247RE rear wheel drive unit works similar to the EPC solenoid, with one exception: It isn t used for line rise. Just like the EPC solenoid, the governor solenoid is ground controlled; that is, the positive feed to the solenoid remains at full system voltage. This voltage comes from a power relay supplying system voltage directly. The control unit controls the ground side of the circuit to raise and lower governor pressure. Test this solenoid the same way you did the Ford EPC solenoid: Connect your positive voltmeter lead to the positive solenoid wire, and the negative lead to the negative wire (figure 8). There should be around 5 to 6 volts with 0 PSI in the governor circuit. As the voltage drops, governor pressure increases. This system has a very sensitive system of checks and balances, so the computer knows exactly how much governor pressure there is at all times. If line pressure to the governor solenoid is high a common situation after a performance modification to line pressure the computer will set an offset code and turn the system relay off. Unlike regular pressure control solenoids, governor pressure is only used to stroke the shift valves. For more information on testing the governor circuit, refer to the articles in the 2001 September and October issues of GEARS. They explain in detail how to check this system. Modulating Shift Solenoids Modulated shift solenoids receive a varying voltage during the shift. They are still onoff solenoids, but the current builds slowly until the solenoid is fully energized. This type solenoid allows the computer to regulate shift feel. The advantage to this type of solenoid is that it works like an orifice or accumulator: By controlling the apply rate of the solenoid, the computer can slow down or speed up a shift, depending on driver s needs. An example of this type of solenoid would be the 32 solenoid (figure 9) used on early 4L60E transmissions. The PCM modulates the current (duty cycle) to control the 32 solenoid on the ground side (figure 10), the same way it does for many other modulating solenoids. The 32 solenoid is off in first gear. In other gears, the 32 solenoid is energized to 90% (figure 11). When the transmission downshifts 32, the signal duty cycle will drop to about 20%. This regulates hydraulic pressure to release the 34 clutch and apply 2 4 band smoothly during the 32 downshift. The computer monitors circuit voltage on these systems when it energizes the solenoid (grounded). If the voltage stays high for 4 seconds, the computer will set a code for that solenoid. You will find this type of solenoid in many units, so make sure you understand the difference between an onoff solenoid and one that is dutycycle controlled. Understanding these electrical tests, and differences between them, can make your job easier. With electrical systems testing, the preset voltages will always be either within spec or they won t. The job is to know where to look when the voltages are out of range, and how the effects will be used in transmission control. Until next time, keep those transmissions in good health! The Doctor Figure 9 Figure 10 Figure 11 82 GEARS September 2003