Gears Magazine - Looking for Information: Allison Prognostics (2023)

We’re all looking for information to help repair the vehicles we face. Often the key to a successful repair is simply a matter of experiencing the symptoms the vehicle is exhibiting or understanding the theory of operation of the system you’re dealing with.

Allison transmissions are available in several speed configurations including 5-, 6-, 7-, and now a 10-speed unit known as the TC10. Many shops hesitate to tackle some of the larger units, such as the Allison 3000 or 4000 series. While these transmissions share much of their design with their smaller brothers, the 1000 and 2000 series units are a little different in some areas.

One thing to keep in mind with Allisons is that they come in several versions. Which one your vehicle is equipped with is usually based on the GVW (Gross Vehicle Weight) and engine horsepower and torque.

While most technicians are comfortable with the 1000, 2000, 3000, 4000, and B-series terminology, it isn’t quite that simple. Allison also has sub-series numbers.

A good example is the 2000-series units. Within the 2000 series there are a wide variety of sub-series units, such as the 2000, 2100, 2200, 2350, 2400, 2500, and 2550 just to name a few. The differences between these sub-series may be minor or could be substantial. In addition, the unit may be one of five generations within that sub-series.

Some of the generational updates may be interchangeable; others aren’t. Some of the features can also vary from year to year as well as model to model, so it’s critical to identify the unit accurately. Like other units, Allison applications have a tag that provides the serial number and model number on early applications. Later model units may not include the model number, so you may have to check the serial number to determine which model it is.

The first two digits will help you ID the unit:

  • 63XXXXXXXX = 1000/2000 Series
  • 65XXXXXXXX = 3000Series
  • 66XXXXXXXX = 4000 Series

Another way to identify the unit is with your scan tool. The scan tool will typically list the Transmission Vocation Model, such as 3000 RDS, 2500 PTS (figure 1).

You can use the numbers and letters associated with the transmission designation to identify the series and sub-series of the transmission, and the vocation or type of service the transmission was designed for. Let’s look at the 3000 RDS as an example (figure 2).

If you’re dealing with a transit bus, it can get even more confusing. Transit buses are designated with the prefix B followed by three additional digits. So a B 400 represents a unit that may be used in a city bus.


Prognostics are features that many Allison transmission computers use to monitor their operation. Many Allison computers are equipped with the prognostics software, which may be enabled or disabled. In our 3000 series example, the system was designed to monitor fluid level and DTCs on most applications. In 2009, features were added to the prognostics software, including:

  • Fluid life
  • Filter life
  • Transmission health

You can display prognostics information via on-board diagnostics or your scan tool. When servicing an Allison, you’ll need to reset some of the prognostics or DTCs may set.

Fluid Level — The system monitors fluid level with a fluid level sensor mounted to the valve body. The sensor is a 5-volt design, with values ranging from 0.5V to 4.5V, depending on the fluid level. Not all applications or years are equipped with a fluid level sensor. If the unit isn’t equipped with a fluid level sensor, fluid level won’t be available.

DTCs — The computer can display DTCs using scan data and on-board diagnostics. How it formats and displays the DTC using on-board diagnostics depends on the transmission generation and the design of the shifter.

Fluid Life/Filter Life — Similar to engine oil life monitoring, the TCM uses a countdown timer to let you know when the transmission fluid should be changed. When the timer reaches 2%, the system displays a “change transmission fluid” message. The system determines filter life by monitoring the pressure drop across the cooler filter circuit. If the filter is restricted, the computer will display a “change transmission filter” message.

Transmission Health — The computer monitors the shift adapt values to determine transmission clutch health. If the shift adapt values reach 10% of the maximum adaptive programmed value, the TCM displays a “transmission health low” message. The prognostic system displays the health of each clutch used.

When the computer recognizes that prognostics service is required, the wrench icon lights on the shifter display. Depending on what’s wrong, the wrench icon may flash (filter life), remain lit all the time (transmission health), or simply come on for the first two minutes of operation (fluid life).

You can retrieve prognostics information with a scan tool or through on-board diagnostics. The on-board diagnostics system can communicate through the shifter.

Several shifter designs and generations have been used, so access to the information will vary slightly. Pushbutton and lever shifter designs have been used. If the shifter doesn’t use a cable, you can access prognostics through the shifter display.


You can access pushbutton shifter prognostics by pressing both up and down arrow buttons simultaneously (figure 3). Once you’ve accessed diagnostics, you can choose which prognostics level, depending on how many times you press the up/down arrows.

  • Oil level: Press the up/down arrows simultaneously once.
  • Oil life: Press the up/down arrows simultaneously twice.
  • Filter life: Press the up/down arrows simultaneously three times.
  • Transmission health: Press the up/ down arrows simultaneously four times.
  • DTCs: Press the up/down arrows simultaneously five times.


You can also use lever-type shifters to access prognostics, provided they aren’t equipped with a cable. To open the menu, press the diagnostics button (Allison logo) on the shifter.

  • Oil level: Press the diagnostics button once.
  • Oil life: Press the diagnostics button twice.
  • Filter life: Press the diagnostics button three times.
  • Transmission health: Press the diagnostics button four times.
  • DTCs: Press the diagnostics button five times.

Some displays can be confusing, depending on the transmission generation. Generation 5 units (2013 and later) are simple to interpret, as all of the information is displayed in a language format.

Generation 4 units (2006-2012) are slightly more difficult, as the displays are segmented. Earlier generations only display oil level and DTCs; you’ll need to access service information to help decipher the displays. Oil level and DTC displays will vary, depending on the computer.

Oil Level: Early applications will require a chart to help you isolate any oil level issues. If oil level is correct, it will be displayed as OL, OK, or “Oil Level OK.”

DTCs: Depending on the display design, the DTC will be displayed in sections: D1=1st code, P=powertrain code, 07=first two digits, 22= last two digits, 1st DTC set P0722. If additional DTCs set, they’ll follow, or pressing the mode button will access the next code. On later designs, the DTC would simply display as P0722.

Oil Life: Oil life will be displayed in a percentage, such as O, 50 O= for oil life 50% (GEN 4); Generation 5 units display as “Oil Life 50%.”

Filter Life: The filter status on GEN 4 units is displayed as F, OK, F=filter. OK indicates the filter isn’t restricted. On GEN 5 units, it’ll be displayed as “Oil Filter OK.”

Transmission Health: The transmission health status on GEN 4 units is displayed as T,OK: T=Transmission, OK indicates the transmission clutches are still functioning within parameters; LO indicates clutch-related issues exist. GEN 5 units will display “Transmission Health Ok” or “Transmission Health Lo.”

As with most built-in diagnostic systems, additional information is available through a scan tool. While scan diagnostics is the desired method, on-board diagnostics can be helpful when a scan tool isn’t readily available.


To reset the oil and filter life, you can use your scan tool, but there are other methods. One way to reset oil life involves the Mode button on some shifter designs. After accessing the oil life display, push and hold the Mode button on the shifter for 10 seconds. Another method is to turn the key on, engine off, and then move the shifter between N-D-N-D-N-R-N.

Filter life follows the same basic process, with one exception: the shifter movement to reset the filter monitor. To reset filter life, access the filter life display. With the key on, engine off, move the shifter between N-R-N-R-N-D-N.

As you can see, working on a larger Allison isn’t that difficult. Yes, there are a few differences, but for the most part, they’re very much like little brothers. Until next time, remember: Success is where preparation and opportunity meet.


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