Hi list/DMC joe I was reading a manual published by Bosch, which covered K jetronic, which said the frequency valve recieves a constant 12v feed and the ECU pulses the ground. If i connect a voltmeter across the terminals, i should get a pulsing 12v? correct?. If there is 12v across the valve, if i connect 12v direct i should be able to feel/hear the valve clicking?. When the valve has no power i assume it is shut, which mean if its not working the engine will run rich? Could this cause the cat to glow red? If there is not 12v at the valve I should check 12v at the lamda relay which runs to the frequency valve? and continuity of both 12v and negative from the ECU to the valve? If the Lambda sensor is not working or disconnected i assume the valve just work as it should when could on a fixed ratio? This should eliminate the sensor if its causing a problem? Thanks Chris Vin 16327