Q: Light green fluid leaked out brake caliper when changing pads

If you opened the bleeder screw on the top of the caliper housing, or you loosened the bolt on the banjo style fitting that holds the flexible brake hose to the caliper, any fluid that leaks from those positions is brake fluid. It is possible that air entered the system if you loosened either fastener and that will cause loss of braking effectiveness. To remove air from the brake hydraulic lines, a low pressure tank is fastened to the brake master cylinder reservoir and brake fluid is forced through the hydraulic lines (under very low pressure, as low as 5 PSI) which has the effect of expelling the air out the bleeder screws. This operation might have to be performed at all 4 wheel positions, depending on how much air entered the hydraulic lines and where the air ended up. If you have ABS brakes, sometimes air can get into the ABS pump and valving and then you must use a bi-directional scan tool to remotely actuate the ABS pump, while bleeding the brakes, to get all the air out. To have this resolved by a certified mechanic, the recommended service is brake bleeding/brake flush. If the issue is not air in the brake lines, obviously the mechanic will still find the cause of the problem that you are writing in about. If you have further questions or concerns, do not hesitate to re-contact YourMechanic because we want you to make the most of your repair dollars and help you to get the best possible results.