Penske's Will Power ended second practice ahead of the IndyCar Grand Prix of Long Beach fastest, ahead of Honda-powered racers James Hinchcliffe and Graham Rahal.
After an interrupted opening session earlier in the day, practice two ran relatively incident-free, with no major incidents or red flags plaguing proceedings.
Points leader Simon Pagenaud ended the session fourth for Penske, despite struggling throughout the day as he chased a more comfortable car set-up.
Team-mate Juan Pablo Montoya, fastest in the morning session, set the early pace in the afternoon, trading times with British racer Jack Hawksworth and Power before slumping to fifth.
Helio Castroneves was sixth on the timesheets, ahead of Josef Newgarden and reigning IndyCar champion Scott Dixon.
Hawksworth, third in opening practice, could only manage ninth fastest for A.J. Foyt Enterprises, with Carlos Munoz rounding out the top 10 for Andretti.
Munoz was just one of a number of drivers clearly pushing beyond the limit in second practice, with Luca Filippi, Tony Kanaan, Pagenaud, Mikhail Aleshin and Montoya all making mistakes and running wide at various points on the street circuit.
Conor Daly ended the session as the fastest rookie in 15th, with former Formula 1 racers Max Chilton and Alexander Rossi 19th and 20th respectively.