IT28G and IT38G Integrated Toolcarriers and 924G, 924GZ, 928G and 938G Wheel Loaders Power Train Electronic Control System Caterpillar

Closed - The switch closes the circuit to ground or the switch closes the circuit to +battery.

Open - the switch opens a circuit to the ECM input.

Downshift Switch

Illustration 1	g00726587
Downshift switch

The downshift switch tells the ECM that the operator wants the transmission to downshift one gear. The downshift switch has one input connection to the ECM.

Auto/Manual Switch

Illustration 2	g00726604
Auto/Manual switch

The auto/manual switch tells the ECM the mode that is selected by the operator. The auto/manual switch has one input connection to the ECM. The operator must select the AUTO position. The machine must then be shifted to neutral in order to activate the AUTO mode.

Shift Lever

Illustration 3	g00328467
Shift lever

In normal operation, the electronics of the shift lever close the gear inputs and the direction inputs on the ECM to ground. The gear and selected direction are the only closed switches. The other direction and gear switches are open. The closed switches tell the ECM the gear that has been selected by the operator.

Switches For Direction Lever ( 928G and IT28G) (Attachment For Remote Forward/Neutral/Reverse Control)

Illustration 4	g00760104
Switch for the direction lever (1) Connector A (2) Connector B (3) Connector C

In normal operation, the switches for the direction lever close the direction inputs on the ECM to ground. The closed switches tell the ECM the direction that is selected by the operator. The ECM then activates the appropriate directional solenoid.

Note: Because two input lines are used for each direction, the ECM can diagnose problems with the circuits for the direction lever. A solenoid for direction is not activated and the transmission remains in neutral if the following actions occur:

• The direction lever does not ground either of the forward inputs or reverse inputs of the ECM.

• The direction lever grounds both the reverse input and the forward input at the same time.

Neutralizer Switch

Illustration 5	g00730228
Neutralizer switch

The neutralizer switch is a two-position switch that is a limit switch and the neutralizer switch is located inside the assembly of the brake pedal valve. The switch is closed to ground when the brake pedal is depressed. The switch is open when the brake pedal is released.

The neutralizer switch is activated when the brake pedal is depressed. This closes the neutralizer input line. The solenoids for direction are not activated and the speed clutch remains activated when the transmission is neutralized.

Note: The neutralizer switch is wired in series with the neutralizer override switch.

Pressure Switches For The Neutralizer

Illustration 6	g00735416
Pressure switch for the neutralizer

The neutralizer function consists of two pressure switches (80 psi and 220 psi). Both of the switches are open when the service brake pedal is released. This allows the transmission to be placed in gear according to the position of the shift lever, the position of the auto/manual switch, and machine speed.

When the 80 psi switch closes, the transmission is neutralized by de-energizing the direction clutch. The transmission remains neutralized until the 80 psi switch opens or until the 220 psi switch closes. If the 80 psi switch opens, the transmission is placed back into gear. If the 220 psi switch closes, the transmission will remain neutralized until the 220 psi switch opens. The transmission is placed back into gear when the 220 psi switch opens.

Neutralizer Override Switch

Illustration 7	g00726604
Neutralizer override switch

When the switch is activated,the neutralizer override switch opens the neutralizer input line of the transmission electronic control module regardless of brake position. This switch is used to disable the neutralizer switch when neutralizing the transmission during braking is not desired.

Ride Control Switch

Illustration 8	g00726666
Ride control switch

The ride control switch signals the mode that is selected by the operator to the ECM. The ride control switch has two input connections to the control: input 1 at connector contact 18 and input 3 at connector contact 19. When the operator selects AUTO mode, input 1 is open and input 3 is closed to +battery. When the ON mode is selected, input 1 is closed to +battery and input 3 is open. When OFF is selected, input 1 and input 3 are open.

Note: A double-pole single-throw switch is used for diagnostic purposes. If the two poles are ever tied to + battery voltage, the control knows that a circuit failure is present. This fault is then shown on the diagnostic indicator. Refer to Systems Operation, "Diagnostic Operation".

Load Check Switch ( 928G and IT28G)

Illustration 9	g00726667
Load check switch

The load check switch signals to the ECM to activate the load check relay. If the engine is dead or there is no hydraulic pressure, the implements can be lowered by activating the load check switch. When the input to the load check (connector contact 19) of the ECM is closed to + battery voltage, the ECM activates the output of the load check relay (connector contact 37). The load check relay energizes the solenoids for the load check.

Parking Brake Limit Switch

Illustration 10	g00726668
Parking brake limit switch

The limit switch for the parking brake is used in order to signal the status of the parking brake to the ECM. If the parking brake is applied and the machine is in gear, the machine remains in neutral. If the machine is shifted into gear and the parking brake is applied, the machine will stay in neutral.