A service diagnostic trouble code sequencer and method is disclosed that includes receiving multiple diagnostic trouble codes (DTCs), determining which DTCs to diagnose first, and recommending which DTC(s) to diagnose first. The sequencer can recommend a category of DTCs to diagnose first, where the category of DTCs includes one or more DTCs. The sequencer can prioritize the DTCs in the category of DTCs. The sequencer can separate the DTCs into multiple categories of DTCs, and prioritize the multiple categories of DTCs. The sequencer can prioritize the DTCs in an ordered category of the multiple categories of DTCs. The sequencer can receive the plurality of DTCs locally or remotely over a network. The sequencer can output the one or more DTCs to diagnose first locally or remotely over a network. The sequencer can be resident on the machine generating the DTCs.