We were asked to carry out a diagnostic evaluation of this Audi RS4 B7 as the cruise control had stopped working . Our initial investigation revealed no significant fault codes related to the cruise control issue . We checked the vehicle using our genuine VAG dealer tool Odis this also allows us to access all available live data  . We preceded to check data relevant to the cruise control operation . The cruise control data all looked normal with the switch operation as expected but one item stood out as incorrect the clutch switch Which showed as being operated all the time irrespective of the clutch pedal position. This vehicle has two switches on the clutch pedal one operates as soon as the pedal is pressed and one that operates when the clutch is fully depressed .

The cruise control switch is the upper white switch

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Lower switch is blue

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We loaded up the wiring diagram from the dealer information system this allowed us to confirm the correct switch wiring colours and the circuit to check to confirm the correct tests required to test the switch operation.

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The switch is connected to the engine ecu which outputs a voltage that is earthed by the switch , the correct supply was present but wasn’t being earthed via the switch this was checked on our Pico scope. A simple resistance check confirmed that the switch had failed . We decided to substitute the switch by connecting the two wires together and observed live data to confirm correct operation this proved that a new switch would resolve this issue .

substituting switch

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Clutch switch live data below

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