master cylinder (or caliper) leak: pedal goes to floor, little or no braking power. air in line: pedal goes to floor, but can be "pumped up" to acheive near-normal braking temporarily. air in the system (or a bad master cylinder) causes the brake pedal to feel soft & spongy, requires brakes to be bled (or m/c replaced)
faulty brake booster: no power assist. very hard pedal, normal or close to normal travel. a bad brake booster turns your brake pedal very hard (feels the same as pumping brakes with the engine turn off). your master brake booster uses the vacuum pressure from the engine's intake manifold; stiff pedal is typically the result of a malfunctioning booster or leaky (or possibly crimped) vacuum hose
Sounds more like air in the system if there is no fault code... let us know.