She's Having My Baby (1) - S6-E1
Continuity mistake: In the prior episode, when Peggy tells Al she is pregnant, Jefferson just smiles at Al after she tells him. In this episode, at the beginning, when Peggy tells Al she is pregnant during the recap, Jefferson smiles at Al but also pats Al on the shoulder.
Answer: It was one of the hoses connected to the engine, nothing specific, but to indicate that Al tampered with the vehicle.