this is part of a HPK service gram from cat that explains how to troubleshoot this problem

Subject:
Conditions that set this code.
How to diagnose this code E-38 ( P1249 ).
Additional troubleshooting information has been added.
DTC E-38 ( P1249 ) may be set when the fuel pressure in the fuel piping/ hose has been
abnormally high for a predetermined amount of time. It may set if the sensing circuit is
detected open.
Abnormally high fuel pressure was detected by the fuel pressure sensor and sets this code
as trip 1.
It would then Illuminate the MIL lamp on the meter panel as trip 2.

Check the fuel pressure with key switch on. Use the Diagnozer diagnostic software to view
LPG fuel pressure.
Note: The fuel pressure it may read higher than 42 kpa. The pressure can spike upward
when you key on and off multiple times.
After cranking the engine begins or as the engine starts, the fuel pressure should begin to
drop to 33 kpa or lower depending on the year of the fuel system.
If it remains high then check actual fuel pressure with a maximum 25 psi. gauge.
The gauge must read 4 to 4.5 psi avg. If in excess of 5 psi then begin looking a high pressure
leakage from the primary to secondary side of the vaporizer assembly.
If pressures are within the normal range then inspect high sensing voltage
( above 5 VDC ) at the fuel pressure sensor.
If sensing voltage is normal then replace the fuel pressure sensor.


Generally it winds up being a defective fuel pressure sensor but the problem could also be as simple as adjusting the pressure at the vaporizer. If all else fails replace the vaporizer and pressure sensor. Clear the codes out of ecm history also.