No there is no air in there, the 603's bleed themselves. It sounds like something got messed up. How do you know it is #4? Did you start the car after doing each one? I would go back and check all 6 just to make sure. Also make sure you torque them right.

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2006 CL500
2009 C300 4matic
1969 280SE
2023 Ram 1500
2007 Tiara 3200