What was found
GE DIAGNOSTICS REPORTS #1 ENGINE TREND DATA SHOWS A DELTA EGT INCREASE AND EGTHDM DECREASE. EGT INDICATION ERRORS ARE SUSPECT. GROUNDED - YES. NO CURRENT FAULTS OR FAULT HISTORY IN #1 ENGINE CDU FAULT CHECK. EGT PROBES READ: S1 - 69.61, S2 - 31.81, S3 - 37.77, S4 - 94.52. PERFORMED EGT PROBE AND SYSTEM INSPECTION REF B737-900 AMM 77-21-01-200-801-F00. FOUND T49.5 PROBE S4 TO BE OUT OF TOLERANCE. REMOVED AND REPLACED T49.5 PROBE S4 REF AMM 77-21-01. OP CHECK GOOD. EGT PROBES NOW READ: S1 - 17.84, S2 - 8.41, S3 - 9.11, S4 - 23.97. ETOPS GROUND VERIFCATION SUCCESSFUL.