A method (201, 401, 50e1) of diagnosing a leakage fault in a pneumatic system, the method comprising: (a) setting a plurality of components (57, 59, 61, 77, 91, 93, 95) served by a common branch (51, 71, 85) of the pneumatic system to a first configuration with a plurality of corresponding valves (63, 65, 67, 81, 103, 105, 107); (b) collectively measuring leakage from the plurality of components (57, 59, 61, 77, 91, 93, 95) in the first configuration; (c) setting the plurality of components (57, 59, 61, 77, 91, 93, 95) served by the common branch (51, 71, 85) of the pneumatic system to a second configuration with the plurality of corresponding valves (63, 65, 67, 81, 103, 105, 107); (d) collectively measuring leakage from the plurality of components (57, 59, 61, 77, 91, 93, 95) in the second configuration; and (e) if the leakage measured with the plurality of components (57, 59, 61, 77, 91, 93, 95) at the first configuration is less than a first configuration threshold value and the leakage measured with the plurality of components (57, 59, 61, 77, 91, 93, 95) at the second configuration is less than a second configuration threshold value, then reporting a pass result, the method being characterised in that it comprises the following additional step: if the leakage measured with the plurality of components (57, 59, 61, 77, 91, 93, 95) at the first configuration is less than the first configuration threshold value and the leakage measured with the plurality of components (57, 59, 61, 77, 91, 93, 95) at the second configuration is greater than the second configuration threshold value, then individually test each of the plurality of components (57, 59, 61, 77, 91, 93, 95) by toggling the component (57, 59, 61, 77, 91, 93, 95) from the state of the second configuration with the state of the remaining components (57, 59, 61, 77, 91, 93, 95) at the state of the second configuration and report a leakage fault result that is determined. (a) setting a plurality of components (57, 59, 61, 77, 91, 93, 95) served by a common branch (51, 71, 85) of the pneumatic system to a first configuration with a plurality of corresponding valves (63, 65, 67, 81, 103, 105, 107); (b) collectively measuring leakage from the plurality of components (57, 59, 61, 77, 91, 93, 95) in the first configuration; (c) setting the plurality of components (57, 59, 61, 77, 91, 93, 95) served by the common branch (51, 71, 85) of the pneumatic system to a second configuration with the plurality of corresponding valves (63, 65, 67, 81, 103, 105, 107); (d) collectively measuring leakage from the plurality of components (57, 59, 61, 77, 91, 93, 95) in the second configuration; and (e) if the leakage measured with the plurality of components (57, 59, 61, 77, 91, 93, 95) at the first configuration is less than a first configuration threshold value and the leakage measured with the plurality of components (57, 59, 61, 77, 91, 93, 95) at the second configuration is less than a second configuration threshold value, then reporting a pass result, the method being characterised in that it comprises the following additional step: if the leakage measured with the plurality of components (57, 59, 61, 77, 91, 93, 95) at the first configuration is less than the first configuration threshold value and the leakage measured with the plurality of components (57, 59, 61, 77, 91, 93, 95) at the second configuration is greater than the second configuration threshold value, then individually test each of the plurality of components (57, 59, 61, 77, 91, 93, 95) by toggling the component (57, 59, 61, 77, 91, 93, 95) from the state of the second configuration with the state of the remaining components (57, 59, 61, 77, 91, 93, 95) at the state of the second configuration and report a leakage fault result that is determined.