It’s an Inside Job - Transmission Digest

It’s an Inside Job

The 2003-and-up Audi A4 and the 2002-and-up A6 with a 1.8- or 3.0-liter engine use a continuously variable automatic transmission known as the Multitronic® 01J (see Figure 1) and also referred to as the VL300. The core of this article is not that this transmission is a CVT. The focus is on what's inside the transmission other than the drive- and driven-pulley set.
It’s an Inside Job

Technically Speaking

Author: Wayne Colonna, Technical Editor

Audi’s Multitronic 01J CVT has the transmission control module within its case

Technically Speaking

  • Author: Wayne Colonna, Technical Editor

Audi’s Multitronic 01J CVT has the transmission control module within its case

The 2003-and-up Audi A4 and the 2002-and-up A6 with a 1.8- or 3.0-liter engine use a continuously variable automatic transmission known as the Multitronic® 01J (see Figure 1) and also referred to as the VL300. The core of this article is not that this transmission is a CVT. The focus is on what’s inside the transmission other than the drive- and driven-pulley set.

When you spin the transmission around, you will find a 25-pin connector sticking out of the rear cover (see figures 2 and 3). This is not a connector for internal electrical components like shift solenoids; this is the transmission control module. Yes, that’s right, the TCM is inside the transmission. Now you may be asking yourself; “Inside the transmission? Wouldn’t it get too hot in there?”

Good question. One reasonable response to this thought is that when you look back at Figure 1, you will notice that this transmission does not use a torque converter! Vehicles with the four-cylinder 1.8-liter engines use a dual-mass flywheel, and those with the 3.0-liter six-cylinder engines use a flywheel/damper-plate assembly. The main heat-producing element has been eliminated, making the TCM’s environment less harsh than what you may have considered originally.

Getting back to the connector, the vehicle harness that plugs into its 25-pin connector supplies power and ground to the TCM. The TCM operates several external relays and the shift-lock solenoid through this harness. The TCM has dedicated lines to send a road-speed signal and receive engine speed. It also interfaces with other computers on the controller area network (CAN), as figures 4 and 5 reveal. And, of course, it has direct control of the transmission.

Now, if it hasn’t hit you yet, you will not be able to do any resistance checks of the solenoids through this connector, just as you wouldn’t with any other computer. The only difference here is that with the computer being inside the transmission, it snaps directly onto the solenoids, eliminating the need for any internal wiring harness, which greatly increases durability. But it also means that the computer has to be removed to gain access to the solenoids for inspection.

With the rear cover off the transmission, you can see that the TCM attaches directly to the valve body (see Figure 6). With the computer off and turned around so you can see the back side, Figure 7 identifies the TCM’s integral components. There you can see the three connectors that plug into the solenoids. These solenoids are very similar in appearance to those of the 01M transmission and slide into the valve body in the same manner (see Figure 8). They each measure between 3.5 and 5.5 ohms.

In various areas of the TCM are the Hall-effect sensors used for the input- and output-speed signals and the multifunction transmission-range signal. The input- and output-speed sensors are activated by sensor rings on the backs of the drive and driven shafts (Figure 9) that easily could be mistaken for seals. Knocking these off with a hammer and screwdriver will ruin your day if you are not careful. Bending them will destroy them. You may have noticed in Figure 7 that there are two output-speed sensors. With two sensors side by side, their signals are out of phase with one another, allowing the TCM to distinguish between forward and reverse rotation.

For the multifunction transmission-range signal, the detent plate (the rooster comb) on the selector shaft contains a magnetic gate that signals four Hall-effect sensors of the TCM to indicate the position of the manual valve. There are a total of 16 different gearshift combinations: Four to recognize the selector positions of P, R, N and D; two to recognize intermediate positions from P to R and from R to N to D; and 10 illegal signals that will cause the TCM to initiate an appropriate substitute program.

Audi refers to the transducers as hydraulic pressure senders 1 and 2. Sender 1 monitors clutch pressure of the forward and reverse clutches, and sender 2 monitors contact pressure in the pulley chambers.

After this review of the TCM’s real estate, a brief explanation of the system’s operational strategy will enhance your understanding of the functions of some of the items we just covered.

As previously mentioned, this variable automatic transmission does not use a torque converter, which means the input shaft spins at the same speed as the engine crankshaft. Forward and reverse clutches change the planetary rotation and deliver engine torque to the drive-pulley shaft inside the transmission (see figures 10 and 11).

With the vehicle at a standstill, the clutch releases, preventing the engine from stalling. As the throttle is depressed, the clutch is pulsed on. That is the function of pressure-control valve (solenoid) 1 shown in Figure 8. This solenoid operates a clutch-control valve in the valve body (Figure 12), which in turn regulates the pressure being applied to the forward or reverse clutch, depending on manual-valve position. When this solenoid is turned off, it no longer can influence the clutch-control valve. The clutch-control valve is then held closed by spring force and blocks pressure from being supplied to the clutch. In other words, this solenoid operates opposite from most pressure-control solenoids we are familiar with. With this solenoid, high control current results in high control pressure, which means high clutch pressure. In fact, all three solenoids are open to exhaust when they are off.

Pressure-control valve (solenoid) 2 operates a valve called a hydraulic reduction valve. This valve controls the pressures going into the drive- and driven-pulley chambers. When the solenoid is fully on, it positions the valve to produce a low ratio. When the solenoid is completely off, it positions the valve to produce a high ratio. As a side note, a hydro-mechanical system called the torque sensor is built into the drive-pulley set. It contains seven steel balls between ramp shells. The drive pulley has a purposely designed exhaust in its pressure chamber. As torque increases, the balls roll into the ramp shells, which gradually close off the exhaust so that full pressure is being applied to the chain during high-torque conditions.

Hydraulic-pressure sender #1 monitors the pressures on the forward or reverse clutch, which pressure-control solenoid 1 operates via the clutch-control valve. Hydraulic-pressure sender #2 monitors the pulley pressure, which pressure-control solenoid 2 controls via the hydraulic reduction valve. This leaves one more solenoid, solenoid valve #1 (see Figure 8).

This solenoid has two functions: It acts as a safety shut-off device and is used for clutch cooling. When this solenoid is fully energized, enough pressure is developed to overcome the spring force on a safety shut-off valve in the valve body. Once stroked, it opens clutch-apply pressure to an exhaust, enabling the clutch to release quickly. When it is used for clutch cooling, the solenoid is energized partially to influence a clutch-cooling valve in the valve body without stroking the safety shut-off valve.

When the clutch-cooling valve is stroked, it transfers pressure from the cooler return pipe into a device called a suction jet pump, otherwise known as an entrainment pump (see Figure 13). This is an elaborate lubrication system that operates according to the Venturi principle. It consists mostly of plastic plumbing and is routed through the different areas of the transmission, almost doubling cooling capability without taxing pump capacity. This is an essential aspect of the transmission’s operation to prevent the forward or reverse clutch from being exposed to excessively high temperatures during slip-control modes, which include stationary, hill-hold and micro slip control.

Hydraulic-pressure senders 1 and 2 provide crucial inputs along with engine speed, transmission input speed, output speed, accelerator-pedal position, engine torque, brake signal and transmission-fluid temperature for slip-control modes to function properly. In fact, the engine-, input- and vehicle-speed signals have backup inputs. The engine-speed signal has its own line into the TCM, and in the event this fails, it also comes in over the CAN bus. The transmission input-speed sensor is backed up by the engine-speed signal.

There are two output vehicle-speed sensors. One is used primarily for speed and the other for direction of rotation. If the sender for speed fails, the sender for rotation becomes a backup. If both fail, a substitute value is generated from the information available on wheel speeds across the CAN bus. The TCM will take certain actions on the basis of which sensor or sensors have failed. Clutch engagements may be controlled by fixed parameters, and the micro-slip control and clutch-adaptation functions and/or the hill-hold function will be deactivated.

Faults that are registered by the TCM are presented in three different ways. The first is a non-critical category in which a substitute program enables continued operation with some restrictions. The driver may notice that the vehicle is driving differently, which may prompt him to have it looked at (that’ll be the day).

The second category also will substitute a program to enable continued operation of the vehicle with restrictions but also will inform the driver of this fault by inverting the selector-lever display on the dash (see Figure 14). This condition is not critical for driving safety or transmission operation, but the fault should corrected.

The third fault again will substitute a program allowing continued operation of the vehicle, at least until it stops. In some instances, after it stops the vehicle no longer will move. In other instances, it will begin to move again after being restarted. The selector-lever display will be inverted and blinking, indicating to the driver that the problem is critical.

That is a brief look at Audi’s VL300 Multitronic 01J variable transmission, where TCM work is an inside job – another look at what’s on the road today and will be in your shop tomorrow.

Many thanks to Thom Mendola and SPX Corp. for letting me tear into their transmission and for the technical information I received from Frank Kuperman of Phoenix Remanufactured Transmissions, making this article possible.

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