What was found
#1 ENGINE ABORTED START WITH FLASHING BOX AT APPOX 45% N2 *NOTE: THIS HAPPENED WHILE USING START CART 11930. GROUNDED - YES. REF B737-900 FIM 80-05-TASK 801. NO DEFECTS NOTED REMOVED AND INSPECTED AND INSTALLED BLEED AIR CHECK VALVE REF B737-900 AMM 36-11-02-000-801/36-11-02-400-801. BLEED AIR CHECK VALVE LEAK CHECK GOOD REF AMM 36-11-02. NO ENGINE PARAMETERS WERE EXCEEDED, REF AMM 71-00-00-740-801-F00. PERFORMED #1 ENGINE START WITH APU AIR SOURCE AND ALL PARAMETERS NORMAL. AIR START CART WAS FOUND TO HAVE LOW PRESSURE OUTPUT.