2005 Commercial Driver’s License Manual Automatic transmission fluid level (may require engine to be running. Check belts for tightness and excessive wear alternator, water pump, air compressor)--learn how much "give" the belts should have when adjusted right, and check each one. Leaks in the engine compartment (fuel, coolant, oil, power steering fluid, hydraulic fluid, battery fluid. Cracked, worn electrical wiring insulation. Lower and secure hood, cab, or engine compartment door. Step 3: Start Engine and Inspect Inside the Cab Get In and Start Engine Make sure parking brake is on. Put gearshift in neutral (or "park" if automatic. Start engine listen for unusual noises. If equipped, check the Anti-lock Braking System ABS) indicator lights. Light on dash should come on and then turnoff. If it stays on the ABS is not working properly. For trailers only, if the yellow light on the left rear of the trailer stays on, the ABS is not working properly.