What was found
DE-ICE PRESSURE CAUTION ILLUMINATED. DE-ICE PRESSURE NORMAL. DE-ICE PRESSURE CAUTION ILLUMINATION ERRATIC THROUGH ALL CYCLES. DIVERTED, LANDING UNEVENTFUL. ATTEMPTED TO RETRIEVE CDS DATA. UNABLE TO ACCESS ICE PROTECTION SYS. (REF FIM 30-10-00-801). GROUND RAN ENGINE AND PERFORMED TEST OF AIRFRAME DEICE SYS IAW AMM 30-11-00-720-801. SYS CHECKED GOOD IN MANUAL MODE. DOES NOT OPERATE IN AUTO MODE. INSPECTED C/P'S AND WIRING AT TMU. NO DEFECTS FOUND. R & R TMU IAW A30-11-01-000-801 & 30-11-01-400-801. NO FAULTS IN CDS. SYS TEST GOOD. RETURNED TO SERVICE. COULD NOT DUPLICATE.