Method of controlling an exhaust fluid treatment apparatus having a diesel oxidation catalyst

An exhaust fluid treatment apparatus has a diesel oxidation catalyst (DOC) having an inlet and outlet. A method of controlling the apparatus comprises: receiving a data value indicative of a temperature at the DOC inlet 210; receiving a data value indicative of a rate of flow of fluid in the DOC 230; receiving a threshold data value indicative of a predicted temperature required for fuel in the DOC to oxidise 220; receiving data indicative of whether the DOC is operating in a first mode, a second mode , or neither of the first or second mode 250; and, when the input temperature is greater than the threshold data value, sending a data value indicative of a quantity or flow rate of fuel to be injected into the exhaust fluid upstream of the inlet for combustion in the DOC 290. The first mode may be a warm-up mode of the DOC and the second mode a running mode of the DOC. The quantity or flow rate of fuel data value may be obtained from a data library comprising a warm-up mode data set 270 and a running mode data set 275.