Method for detecting an isolation fault in an isolation resistance between a positive and negative high-voltage bus rail (5, 6) and a vehicle chassis on a high-voltage propulsion side of a high-voltage system of an electric or hybrid-electric vehicle, wherein the high-voltage system is split into a high-voltage battery side and the high-voltage propulsion side by means of first and second high-voltage contactors (7, 8) located in the positive and negative high-voltage bus rails (5, 6), respectively, wherein the high-voltage propulsion side comprises a first and second capacitors (9, 10) connected in series across the positive and negative high-voltage bus rails (5, 6), and wherein a common junction of the first and second capacitors (9, 10) is connected to the chassis, characterised in that the method comprises: ensuring that first and second high-voltage contactors (7, 8) are set in an open state, operating an isolated DC/DC converter for converting a supplied high-voltage from a high-voltage battery of the high-voltage battery side to a low-voltage output on the high-voltage propulsion side, supplying the low-voltage output to the positive and negative high-voltage bus rails (5, 6) for simultaneous charging of the first and second capacitors (9, 10), registering a charging current, voltage level or energy level of the first and second capacitors (9, 10), and determining, based in the registered charging current, voltage level or energy level of the first and second capacitors (9, 10), whether an isolation fault between the positive and/or negative high-voltage bus rail (5, 6) and the vehicle chassis on the high-voltage propulsion side of the high-voltage system is present. wherein the high-voltage system is split into a high-voltage battery side and the high-voltage propulsion side by means of first and second high-voltage contactors (7, 8) located in the positive and negative high-voltage bus rails (5, 6), respectively, wherein the high-voltage propulsion side comprises a first and second capacitors (9, 10) connected in series across the positive and negative high-voltage bus rails (5, 6), and wherein a common junction of the first and second capacitors (9, 10) is connected to the chassis, characterised in that the method comprises: ensuring that first and second high-voltage contactors (7, 8) are set in an open state, operating an isolated DC/DC converter for converting a supplied high-voltage from a high-voltage battery of the high-voltage battery side to a low-voltage output on the high-voltage propulsion side, supplying the low-voltage output to the positive and negative high-voltage bus rails (5, 6) for simultaneous charging of the first and second capacitors (9, 10), registering a charging current, voltage level or energy level of the first and second capacitors (9, 10), and determining, based in the registered charging current, voltage level or energy level of the first and second capacitors (9, 10), whether an isolation fault between the positive and/or negative high-voltage bus rail (5, 6) and the vehicle chassis on the high-voltage propulsion side of the high-voltage system is present. ensuring that first and second high-voltage contactors (7, 8) are set in an open state, operating an isolated DC/DC converter for converting a supplied high-voltage from a high-voltage battery of the high-voltage battery side to a low-voltage output on the high-voltage propulsion side, supplying the low-voltage output to the positive and negative high-voltage bus rails (5, 6) for simultaneous charging of the first and second capacitors (9, 10), registering a charging current, voltage level or energy level of the first and second capacitors (9, 10), and determining, based in the registered charging current, voltage level or energy level of the first and second capacitors (9, 10), whether an isolation fault between the positive and/or negative high-voltage bus rail (5, 6) and the vehicle chassis on the high-voltage propulsion side of the high-voltage system is present.