What was found
ACARS MESSAGE: NR 2 EGT 50 DEGREES HOTTER THAN NR 1 EGT. DETERMINED THAT NR 1 ENGINE, "B" CHANNEL, EGT PROBE S4 IS CAUSING INDICATION DISPARITY. READS 109.22 DEGREES C STATIC. GROUNDED-YES. ACCOMPLISHED T495 ENGINES BITE TEST INPUT MONITORING: ENGINE NR 1 READS S1- 88.83 S2- 46.23 S3- 53-20 S4- 109.68; ENGINE NR 2 READS S1- 99.35 S2- 50.81 S3- 52.11 S4- 98.42. REPLACED ENGINE NR 1 "S4" PROBE, REF B737-900 AMM 77-21-01-400-801-F00. OPERATIONS NORMAL, REF AMM 73-21-00-700-804-F00. ENGINE NR 1 NEW INPUT READINGS READ: S1- 30.01 S2- 16.80 S3- 17.66 S4- 39.80.