Models: XJ/X351, XF/X250 with air suspension
Issue: If the battery supply to the vehicle is disconnected for any reason, the Chassis Control Module (also known as the Air Suspension Module or Suspension Module Integrated Suspension Control Module (CHCM) may not power-up correctly. As a result, a scan tool will report no communication with the CHCM module in several session screens. This will only affect a small percentage of cars and on an intermittent basis.
The vehicle may also display error messages on the cluster relating to suspension and adaptive dynamics faults: “SUSPENSION FAULT Max Speed 30 MPH” or “Adaptive Dynamics Fault.” The SDD tool may also log code U012A-00 from modules which communicates with the CHCM.
The power-up strategy currently in place for the CHCM and CHCMB can cause this concern.
To resolve the issue, fully disconnect the negative lead from the battery terminal. Wait for 5 minutes and re-connect the battery negative. Repeat this process if necessary. Ensure that a power supply unit is NOT connected to the vehicle when doing this. A scan tool should confirm communication with the CHCM and CHCMB (note: the CHCMB is optional) and cluster error messages will no longer appear.
Courtesy of Mitchell1