Information on 6.6L Duramax LLY Diesel Engine Fire Truck Application Power Take-Off (PTO) Modification to Add-On 3rd Gear Drive for Split Shaft Pump

The following service information outlined in this bulletin is divided into three procedures and will aid technicians in modifying the PTO for a 3rd gear drive for a split shaft pump. The modifications will allow the vehicles listed above to be used for a Fire Truck application.

It will be necessary to modify the existing vehicle wiring and have an Allison® distributor reprogram the TCM with the correct software calibration into the vehicle. Refer to Procedure #2 in this bulletin for a new vehicle or a vehicle with no previous PTO wiring modifications.

Procedure #1 - Check for prior PTO modifications:

Important: Vehicles that may have PTO equipment installed, check the wiring to determine if it has been modified to add a relay for the PTO operation per Bulletin06-08-131-001A . Modify the wiring as necessary and have an Allison Distributor reprogram the TCM with the correct software calibration into the vehicle.

1. With the ignition OFF, disconnect the TCM connector (80-way) and locate terminal 21.
2. Disconnect PCM connector J1 and locate terminal 08.
3. Using the proper probe tools, use a Digital Multimeter and check for continuity between TCM terminal 21 and PCM terminal 08.
4. If there is continuity, the system has not been modified. Refer to Procedure #2 in this bulletin if the vehicle is new or has had no wiring modifications (Original wiring) for the PTO per Bulletin 06-08-131-001A.
5. If there is no continuity, the system has been modified. Refer to Procedure #3 in this bulletin. The vehicle has had wiring modifications for PTO per Bulletin 06-08-131-001A.

Procedure #2 - Vehicle is new or has had no wiring modifications for PTO per Bulletin 06-08-131-001A:

Refer to Repairing Connector Terminals in the AFL/EPC Connector repair section of SI for information on connecting terminals to wires.

1. Move wire 2522 from TCM pin 21 to Pin 43.
2. Check the wiring connections using the proper probe tools, ensuring continuity between Upfitter Connector pin "G" to TCM pin 43.

Important: It is critical that any calibration changes occur at an Allison distributor to ensure the change is linked to the vehicle identification number (VIN) for any future service repairs.

3. After the split-shaft pump has been installed, have an Allison Distributor flash the correct software calibration into the vehicle.

Procedure #3 - Vehicle has had wiring modifications for PTO per Bulletin 06-08-131-001A:

Refer to Repairing Connector Terminals in the AFL/EPC Connector repair section of SI for information on connecting terminals to wires.

1. Remove the relay in circuit 2522.
2. Splice a wire from relay normally open terminal (continuity to TCM terminal 21) to wire for relay power feed (continuity to Trans Opt connector C).
3. Move the wire from TCM terminal 21 to TCM terminal 43.
4. Check the wiring connections using the proper probe tools, ensuring continuity between Upfitter Connector pin "G" to TCM pin 43 and PCM pin J1-08.

Important: It is critical that any calibration changes occur at an Allison distributor to ensure the change is linked to the vehicle identification number for any future service repairs.

5. After the split-shaft pump has been installed, have an Allison Distributor flash the correct software calibration into the vehicle.

Additional Information On third gear lockup:

Special transmission operation (third range lockup) with operation request for split shaft PTO operation (PTO mode switch), plus indication of pump engagement (PPE switch). In the process of installing a split shaft pump there are other connections that will need to be completed. Refer to the information below for circuit requirements for split shaft pump applications.

The third range lockup is enabled when circuit 1479 is switched to send power to the TCM, and a switch is closed to complete the circuit between TCM pump enable circuit and signal return circuit 476. When this function is enabled and a specific set of conditions exist (listed below), the TCM will command the transmission to operate in 3rd gear lockup. The switch on circuit 1479 reflects the selection of pump mode by the operator. It typically is also interlocked with the park brake to assure the brake has been engaged before pump mode can be requested. The separate positive pump engagement (PPE) switch denotes the completion of the split shaft PTO shift (PTO is physically fully engaged). A second set of contacts on this same switch is used to control illumination of the "OK to Pump Lamp". Required operation conditions for enabling the function are:

Function response to TCM power interruption (power off, followed by power restored) are:

System Operation

To Engage:

1. Transmission shifted to neutral.
2. Apply park brake.
3. Select pump with dash switch. Turns on "Pump Mode Requested" light. Turns on input signal to TCM, which requests pump mode. When split shaft shifts, pump enable circuit is activated and the "Pump Engaged" light is turned on.
4. Select drive. Transmission shifts to 3rd lockup. "OK to Pump" light is turned on.

To Disengage:

1. Transmission shifted to neutral.
2. Select road mode. PTO disengages. If output shaft rotation continues, press the "Momentary Trans Brake" switch before selecting road mode. This will cause the transmission output shaft to stop if the transmission is in neutral and output shaft speed is less than 175 rpm.