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Zero-field muon spin relaxation (µSR) measurements were carried out on the Pr_xLa_1-xPt₄Ge₁₂ alloys, revealing a second-order like suppression of broken time reversal symmetry (TRS) on approaching x = 0. For x > 0.3 compounds, the onset temperatures of time-reversal violating phase is lower than the superconductivity (SC) transition temperatures. Both temperature dependence of upper critical field H_c2(T) and lower critical field H_c1(T) in x > 0.3 alloys have two different quadratic temperature regions. The SC order parameter of PrPt₄Ge₁₂ is then discussed in the context of TRS phase determined by µSR measurements, H_c2(T) and H_c1(T) results, and gap point nodes illustrated by our specific heat data (down to 0.1 K).