54 4 Making Matters Speak in Railway Maintenance Johan M. Sanne Introduction In this chapter diagnostic practice is conceptualised as the means to ‘make matters speak’: how practitioners make sense of problems through recognising and ordering significant cues from the material stuff that they investigate (Latour, 2004). The chapter is based upon an analysis of ethnographic data of railway maintenance in Sweden. I focus on technically difficult cases, elucidating railway technicians’ diagnos- tic work through the concepts of situated learning and heterogeneous engineering. The situated learning perspective has emphasised the use of resources such as storytelling, an intimate knowledge of technology, or the use of various sensory cues in diagnostic work (Barley, 1996; Orr, 1996; Mellström, 2002; Henning, 1998). However, it remains unclear exactly how these resources are combined to solve technical problems. To this end, I draw on the notion of heterogeneous engineering – where various elements are amalgamated in a network that can explain the problem (Law, 1987). I highlight the balance of elements that support and threaten the stability of the network (or explanation) to understand this aspect of diagnostic work. I begin by discussing how insights from situated learning research help us to comprehend diagnostic practices and suggest how the notion of heterogeneous engineering can enrich this understanding. To this aim I describe my ethnographic methods and how I achieved rapport in a safety-critical and hazardous occupation along with emphasising the value of difficult cases in appreciating diagnostic practices. I then analyse three cases of diagnosing technical problems, focusing on the contingent combination of different resources. Finally, I outline the theoretical as well as the practical implications. 9780230_223288_05_cha04.indd 54 9780230_223288_05_cha04.indd 54 10/28/2009 6:12:45 PM 10/28/2009 6:12:45 PM