Where do you add the oil for the trx400ex?

To add oil to a Honda TRX400EX, locate the oil filler cap, which is typically found on the right side of the engine near the rear. Remove the cap and use a funnel to pour in the appropriate type and amount of oil, as specified in the owner's manual. After adding oil, check the dipstick to ensure the oil level is within the recommended range before replacing the cap.