CX31 and CX31 HT On-Highway Transmissions Transmission Control Caterpillar

Transmission Control
CX31 and CX31 HT On-Highway Transmissions [SEBU9206]
CX31 and CX31 HT On-Highway Transmissions Transmission Control

Illustration 1g02512859
(A) LED in transmission gauge is yellow
(B) RED - Stop engine, Amber - MIL light, Amber - Warn engine, Amber - Traction control
(C) Will display 'Engine failure' or 'Transmission failure' in the upper and lower section depending on whether the engine or transmission has the fault.

Warning Light Indicator

There will be two warning light indicators on the truck dash. These two indicators will be engine icons and the words ""Trans Failure"" will show in the red LCD odometer when a transmission issue is present. One of the engine icons will be an ""AMBER"" warning and the other icon will be a ""RED"" stop engine.

  1. AMBER Caution Lamp

    The diagnostic lamp is yellow or AMBER. The diagnostic lamp will communicate the status of the transmission electronic system. If the amber lamp (trouble code) is activated, the lamp alerts the operator that a diagnostic condition is active within the transmission. The amber lamp does not require immediate operator attention, but normal operation of the transmission may be affected.

  2. RED Warning Lamp

    The RED warning lamp warns the operator of conditions which require immediate attention. The warning lamp indicates either a transmission blocked oil filter bypass or an excessive oil temperature. Immediate operator action is required in order to reduce the temperature of the transmission oil or immediate action is required to service the oil filters.


The transmission control in Illustration 3 is the operator interface for AVSpare's CX series transmissions.

  • The CX31 Transmission Shift Selector Pad has six operator buttons and a two-digit display.

  • N Button (The N activates transmission neutral. Pressing this button will cause the transmission to shift to neutral.)

  • D Button (The D activates transmission forward gears. Pressing this button will cause the transmission to shift into the lowest programmed forward gear.)

  • R Button (The R activates transmission reverse gear. Pressing this button will cause the transmission to shift into the reverse direction gear.)

  • Mode Button (The Mode button is used to access different shift modes or operational modes that are available in the transmission software. This button has an embedded Red LED that will illuminate indicating that the Mode Button has been pressed.) Refer to the Electronic Programming guide for more information.

  • Arrow Buttons (The Arrow buttons are used to upshift or downshift the transmission one gear per activation.) The arrow buttons are used to adjust the maximum gear manually that the transmission will attain. Pressing "D" will return the maximum gear to the top gear available (6th gear in the CX31).

Basic Operation

With the ignition key switch in the ON position, the Shift Selector Pad will display a pair of N's on the display. The display indicates that the transmission is in Neutral.

Illustration 2g03449039
Shift Pad
(54) Left character
(55) Right character

Range Selection

To shift t transmission into a desired Range or Gear, the operator pushes the D for Forward or the R for Reverse.

Note: The transmission will not shift into a range from Neutral or between D and R if the rpm is over 1000 rpm on the engine.

Forward Range

When in forward range, the operator request a downshift by pressing the down arrow on the shift selector pad. Press the down arrow until the left display digit in the display (desired top gear limit) is lower than the right digit in the display (actual gear). The transmission will downshift to the new top gear limit as soon as the transmission is able to do so without over speeding the engine. Pressing "D" will return the desired top gear limit to the maximum gear available.

Illustration 3g01300849

The Actual Gear will be displayed on the right side of the transmission as the transmission shifts.

Reverse Range

To select the Reverse Range, the operator selects the R button.

When the transmission shifts into Reverse Range, the display will have an R in both locations. There is only one gear in the Reverse range.

Illustration 4g01300906

Illustration 5g01301022

Flashing Desired Gear

Several circumstances may prevent the transmission from shifting into a desired Range. When trouble shifting occurs, the Desired Gear value will flash and the transmission will not shift into the selected range.

Illustration 6g01394825

Circumstances preventing the transmission from a shift into the desired range include the following:

  • Engine speed too high

  • Vehicle speed too high

  • Programmable parameters

  • Neutralized by parking brake

  • Auto Neutral

  • PTO

  • Driveline PTO

  • Neutral to gear inhibit

  • Direction inhibit

Once the switch and speed requirements have been met, the transmission will shift normally. Some circumstances may require the operator to select Neutral range and then reselect the desired range for the transmission to shift into that range.

Note: If the Left character “flashes” N, then the transmission is locked in Neutral by the ECU. The most common cause of a “flash” N is when the parking brake is applied. To resume operation, press the N button before the D or R button in order for the D or R button to respond. The parking brake will still need to be released before driving the vehicle. There are other operations that may cause the “flash” N to be displayed based on how the OEM has requested the ECU to be programmed. See Special Instruction, REHS2884, "Application and Installation Guide (Electrical)" for additional information about the Operator Shift Pad.

Additional Features


The mode functions listed in this OMM may or may not be available based on the customer programming provided.

Mode Button

The Mode button is available to control various functions provided by the customer programmer. The primary purpose of the mode button is to select a different shift schedule designed to improve fuel economy. Other modes may be selected through transmission parameter programming. When the Mode button is pushed, the LED in the upper right corner of the Mode button turns ON. The “ON” LED light informs the operator that the selected feature is active. Pressing the Mode button a second time will disable the feature and the LED will turn off.

Illustration 7g01301284

Economy Mode

Selecting the Economy mode will reduce the engine speed at which the transmission shifts in order to provide earlier upshifts. Selecting the Economy mode will enhance fuel economy.


Selecting the PTO mode will engage the control of PTO devices.

Note: This functionality is only available if the PTO is controlled by the transmission ECU.

Hold In Gear

The Hold In Gear feature is used to enable the operator to limit upshifts of the transmission. The transmission will hold the current gear and only upshift to prevent an engine overspeed condition. Normal downshifting is allowed as the vehicle speed decreases. As the transmission downshifts, the hold continues which means that the transmission will stay in the downshifted gear until a mode change is requested, or an overspeed of the engine requires an upshift. The Mode button is used to enable the Hold In Gear feature. If the operator presses and releases the Hold button a second time or selects a different gear, the Hold function will be disabled. When the Mode button is used as the switch, activating the Hold function will enable the Mode button LED. This LED will remain enabled as long as the Hold feature is active.

Quick First Gear Limit

The Quick Gear Limit feature may utilize the shift pad MODE switch activation to indicate that the transmission should not upshift beyond first gear. This feature can be used to limit vehicle speed during refuse applications. The Quick Gear Limit feature only inhibits upshifts past first gear. If the transmission is in second gear, the transmission will continue to operate normally until first gear is attained, at which time upshifts will be inhibited. The Quick First Gear Limit feature may be programmed by OEM vehicle manufacturers to either Enable or Inhibit Reverse gear. Vehicle operation conditions that cause the engine to overspeed in first gear will result in an engine protection upshift to higher gears.

Oil Level Check

The AVSpare Shift Selector Pad allows the operator to check the oil level of the transmission from the operator station by using an electronic oil level sensor (internal to the transmission).

Vehicle requirements for initiating the Oil Level Check

  1. Engine at idle

  2. Vehicle stationary

  3. Transmission Oil Temperature more than 80 °C (176 °F)

  4. Vehicle on Level Ground

  5. Transmission in Neutral

To initiate the transmission oil level check, simultaneously press and release the Up and Down arrows on the Shift Selector Pad. This action starts a two-minute timer. If conditions are not correct for the oil level check to take place, the Shift Selector Pad will display one of the following using the range display. The display will only display two characters at a time.

Table 1
Display  Description 
OL-ES-LO  Engine speed too low 
OL-ES-HI  Engine speed too high 
OL-TX-N  Neutral not selected 
OL-OT-LO  Oil temperature too low 
OL-OT-HI  Oil temperature too high 
OL-VS-HI  Vehicle speed not zero 
OL-SE  System error 

Once all conditions are met, the range display will show 90 and will count down to 0 during the two-minute counter period. At the end of two-minute countdown, one of the following will be displayed using the range display, two characters at a time.

Table 2
Display  Description 
OL-LO-XX  Oil Level is low by XX quarts 
OL-HI-XX  Oil Level is high by XX quarts 
OL-OK  Oil Level is full 

The Oil Level Message continues to display until the operator exits the mode by pressing a range button or the Up/Down arrows simultaneously. The transmission will not require action taken at the end of the oil level check. This check is for the operator information. The operator is responsible to take any appropriate action for an indicated oil level that is either high or low.

Note: The manual dipstick is used for initial fill to get close to the desired level.

Display Illumination

The display illumination level is normally tied to the dash illumination level control. An optional vehicle mounted switch, if so equipped, may be used to disable the display.

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