Transferring torque during a driveline system error

1. A method for controlling a vehicle driveline system, comprising:

determining an error within the system;

following the error, determining that a state of a power take-off unit (PTU) within the system is determinable, wherein determining that the state of the PTU is determinable comprises determining whether to trust any received electrical data associated with identifying the state of the PTU; and then

transferring a torque from the PTU to a secondary drive unit (SDU) during the error.

2. The method of claim 1 , wherein the error occurs at the PTU, wherein the torque is a normal torque, wherein transferring the normal torque from the PTU to the SDU comprises transferring a determined or predetermined quantity of torque which the PTU otherwise would transfer in an absence of the error or in an absence of a PTU diagnostic trouble code (DTC).

3. The method of claim 1 , further comprising: prior to transferring the torque, determining the state of the PTU, wherein the state comprises one of an engaged state or a disengaged state.

4. The method of claim 1 , further comprising: determining that the state is determinable based on determining that the error is a position error at the PTU or a power draw error at the PTU.

5. The method of claim 1 , further comprising:

determining that the state of the PTU is an engaged state; and then

controlling the PTU to transfer the torque to the SDU.

6. The method of claim 5 , wherein controlling the PTU to transfer the torque to the SDU comprises at least one of: outputting from a computer a torque reduction override instruction, or controlling an actuator at the PTU to deliver the torque.

7. The method of claim 1 , further comprising: after determining the error, transferring the torque to the SDU, based at least in part on electronic traction control sensing.

8. The method of claim 1 , further comprising:

after determining the error, receiving an indication of a driver input to change to a two-wheel drive (2WD) mode; and then

controlling an actuator of the SDU to change to the 2WD mode.

9. A system for controlling a vehicle driveline, comprising:

a computer, comprising a processor and memory storing instructions executable by the processor, the instructions comprising, to:

determine an error within the system; and

following the error, determine that a state of a power take-off unit (PTU) is determinable; and then,

transfer a torque from the PTU to a secondary drive unit (SDU) during the error, wherein determining that the state of the PTU is determinable comprises determining whether to trust any received electrical data associated with identifying the state of the PTU.

10. The system of claim 9 , wherein the error occurs at the PTU, wherein the torque is a normal torque, wherein transferring the normal torque from the PTU to the SDU comprises transferring a determined or predetermined quantity of torque which the PTU otherwise would transfer in an absence of the error or in an absence of a PTU diagnostic trouble code (DTC).

11. The system of claim 9 , wherein the state comprises one of an engaged state or a disengaged state.

12. The system of claim 9 , wherein the instructions further comprise, to:

determine that the state of the PTU is an engaged state; and then

control the PTU to transfer the torque to the SDU.

13. The system of claim 12 , wherein controlling the PTU to transfer the torque to the SDU further comprises at least one of the instructions, to: output a torque reduction override instruction, or control an actuator at the PTU to transfer the torque.

14. The system of claim 9 , wherein the instructions further comprise, to:

receive an indication of electronic traction control sensing; and

after determining the error, transfer the torque to the SDU, based, at least in part, on the sensing.

15. The system of claim 9 , wherein the instructions further comprise, to:

receive an indication of a driver input to change to a two-wheel drive (2WD) mode; and then

control an actuator of the SDU to change to the 2WD mode.

16. The system of claim 9 , wherein the instructions further comprise, to:

prior to determining that the error occurred within the system, determine whether the error was a system level error; and

when the error is a system level error, then suspend use of the SDU.

17. The system of claim 16 , wherein the instructions further comprise, to:

suspend use of the SDU for a remainder of a current ignition cycle when a type of the error is a latched error type; and

provided the error is first cleared, suspend use of the SDU for a portion of the current ignition cycle when the type of the error is an unlatched error type.

18. A vehicle driveline system, comprising:

a secondary drive unit (SDU); and

a computer, comprising a processor and memory storing instructions executable by the processor, the instructions comprising, to:

determine an origin of an error in the vehicle driveline system;

when the origin of the error occurs in a power take-off unit (PTU), then determine that a state of the PTU is determinable, wherein determining that the state of the PTU is determinable comprises determining whether to trust any received electrical data associated with identifying the state of the PTU; and

when the state of the PTU is determinable, then transfer a torque from the PTU to the SDU during the error.

19. The system of claim 18 , wherein the instructions further comprise, to:

when the origin of the error occurs in the SDU, then disengage a clutch of the SDU;

determine a type of the error is one of a latched type error or an unlatched type error; and

when the type is the latched type error, then actuate the PTU to a disengaged state so that a drive shaft of the system is not driven by the PTU while the clutch is disengaged.

20. The system of claim 18 , wherein the instructions further comprise, to:

when the origin of the error occurs in the SDU, then disengage a clutch of the SDU;

determine a type of the error is a latched type error; and then

determine that an actuation of the PTU to a disengaged state has been inhibited.

21. The system of claim 18 , wherein transferring the torque to the SDU further comprises at least one of the following instructions: to output from the computer a torque reduction override instruction, or to control an actuator at the PTU to deliver the torque.