What was found
D: Phx- Air turnback - Flt 494 - Shortly after take off EICAS displayed Air/ Ground Disagree message, FRM code 32-09-03-00, and the aircraft returned to Phx. C: In Phx maitenance trouble shot and performed a bite test of the PSEU which showed no faults when faults should have existed. The PSEU was replaced. As a precaution both NLG not compressed sensors were replaced as well.Part name: Sensor(2ea) MFG: ELDEC Corp. P/N:8-345-01 Part Loc: NLG Part condition: Good (Precautionary)