Scania ALLISON DTC 1821 Gear changing prevention function

ALLISON Allison automatic gearbox · Scania

Code 1821 (decimal). Some diagnostic tools show it in hexadecimal as 071D.

In short

Input signals to the control unit for activation of the gear changing prevention function are incorrect.

Applies to: A4

What does Scania ALLISON fault code 1821 mean?

Input signals to the control unit for activation of the gear changing prevention function are incorrect.

What causes Scania DTC 1821?

The control unit has detected two different states on pins 1 and 42 in the control unit.

How does the system react?

The Allison fault code number is: P071D. The gear change prevention function is activated when pins 1 and 3 are connected together and pin 42 is connected to earth. The fault code can only be set if the control unit in the vehicle has been programmed for fire engines. The fault code is cleared automatically when the vehicle has completed 40 start-up cycles without the fault being detected again.

How to fix Scania ALLISON fault code 1821?

  1. Check that there is no damage or short circuits in the external cable harness or any switch connected to pins 1, 3 and 42.
  2. If no fault is detected, contact an Allison dealer.

This information is for guidance only. Always follow the manufacturer workshop manual and safety procedures; if in doubt, contact an authorised workshop.