Any bit of sand or dirt can keep the diaphragm from sensing the correct pressure. Often the output a contaminated transducer will be linear up to a certain pressure, but then the output stops changing. Simply disassemble the transducer and clean the sensor cavities. Body bolt torque is also important. The DP15 transducer, for example, requires 115 inch-pounds of torque on each of the four body bolts.
Less torque means that there is less clamping force on the diaphragm.
This allows the diaphragm to slip out from between the coil housings during full scale pressure excursions. Excessive hysteresis and non-linearity often result. If still out of spec replace diaphragm. See Torque Guidelines. See Torque Guidelines.