In the present study we aimed to investigate phonological substitution errors made by hearing second language (M2L2) learners of American Sign Language (ASL) during a sentence translation task. Learners saw sentences in ASL that were signed by either a native signer or a M2L2 learner. Learners were to simply translate the sentence from ASL to English. Learners’ responses were analysed for lexical translation errors that were caused by phonological parameter substitutions. Unlike previous related studies, tracking phonological substitution errors during sentence translation allows for the characterization of uncontrolled and naturalistic perception errors. Results indicated that learners made mostly movement errors followed by handshape and location errors. Learners made more movement errors for sentences signed by the M2L2 learner relative to those by the native signer. Additionally, high proficiency learners made more handshape errors than low proficiency learners. Taken together, this pattern of results suggests that late M2L2 learners are poor at perceiving the movement parameter and M2L2 production variability of the movement parameter negatively contributes to perception.