What was found
ON TAKEOFF FROM SFO LEFT AUTOTHROTTLE WOULD NOT MOVE FORWARD TO TAKEOFF POSITION AND RED AUTOTHROTTLE ANNUNCIATOR ILLUMINATED. TRIED TO RESET SEVERAL TIMES BUT WAS UNSUCCESSFUL. GROUNDED - YES. AUTO THROTTLE BITE TEST HAS MSG 22-31263. ACCOMPLISHED B737-800 FIM TASK 22-31 TASK 810, OP CHECKS GOOD. ACCOMPLISHED AUTO THROTTLE SYS OPERATIONAL TEST, OPS NML REF B737-800 AMM 22-31-00-710-801. ACCOMPLISHED DFCS DFCS/AT LRU REPLACEMENT TEST, GRP BITE 35, ALL TEST PASSED REF AMM 22-11-00/201.