Abstract: By disassembling sufficient L-type vehicle power unit malfunction components, it is concluded that the main cause of the failure is poor heat dissipation of the internal IPM module. Based on the shortcomings of current overhaul and maintenance methods, targeting power unit failure causes, vehiclemounting standards for power unit IPM module is established, and measures such as cleaning heat sink, changing thermal silica, withdrawing bad performance IPM module in time are proposed, which effectively solves the inertial failure problem of L-type vehicle traction system power unit burning down. Practice results have verified the efficacy of new overhaul and maintenance mode.