Gearbox pressure switch 1 (PS1), circuit low
Check that the cable harness between the gearbox and the control unit is not damaged.Contact an Allison dealer.
What you'll see
No driver-visible symptom recorded.
System reaction
The Allison fault code number is: P0842.The control unit sets the fault code when it detects that PS1 is not pressurised under any of the following circumstances: Clutch C5 is filled and the PCS2 solenoid is commanded ON.Clutch C5 is drained and both locking valves are on.After a change in the state of the locking valves which means that both locking valves are on.For the fault code to be set, the following conditions must be met: The hydraulic system is pressurised.Reset is completed.The oil sump temperature is higher than -15°C.The lock-up cannot be locked. The control unit shuts off gear changing adaptation. The control unit attempts to engage the previous gear.While the fault code is active, the control unit ignores all information from the drive mode selector. The fault code is cleared automatically, when the vehicle has completed 40 start-up cycles without the fault being detected again.
Diagnostic depth
PS1 is not pressurised when it should be.
A possible cause of the fault may be damage in the cable harness or a defective PS1.