What was found
ATTEMPTED THREE COLD SOAK STARTS ON THE APU AT FL 400, ALL THREE ATTEMPTS RESULTED IN FAULT LIGHTS ILLUMINATING. REMOVED AND REPLACED IGNITION UNIT REF MM 49-41-31. PERFORMED FIM TASK 49-40 TASK 85. DISCONNECTED D10434 AND P13. CHECKED PINS 16/17 AND 2/1. NO FAULTS FOUND. REINSTALLED BOTH PLUGS D10434 AND P13. PERFORMED APU BITE TEST 49-60 TASK 801. FAULT 49-41181 STILL ACTIVE. SUGGEST REPLACING IGNITION CONTROL UNIT. PERFORMED APU GROUND START FOUR TIMES FAULT NOT ACTIVE. SYS CHECKED NORMAL. REF 49-11-00-710-801. SYS RETURNED TO NORMAL.