Pressure switch 1 (PS1), circuit high
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: P0843.The control unit sets the fault code when it detects that PS1 is pressurised under any of the following circumstances: Clutch C5 is drained and the PCS2 solenoid is given the instruction OFF and at least one of the locking valves for C1 or C2 is switched off.After a change in the state of the locking valves, which begins with both locking valves being on and which ends with at least one of the locking valves for C1 or C2 switching off.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 locks the current 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 pressurised when it should not be.
A possible cause of the fault may be damage in the cable harness or a defective PS1.