I recently took my newly aquired old neglected volvo 760 1990 to get a sticker. I failed the emissions test. With a high NOx level. Everything I have read indicates this is the egr valve/sensor failure. I ordered the factory service manuals from volvo for this vehicle, but they barely apply to my car. I figured out that the vacumn pump in my car is not connected to anything and is just for ornamentation in my turbo Model. I unhooked the EGR valve from the two large hoses and looked iside=all clear, valve works. I am trying to determine if the 2 prong electrical connector on the rear of the Valve is the Positive Temperature Coefficient sensor or if it is a 12 volt voltage source to control EGR valve. I disconnected wires from EGR and tried to get a voltage. I got nothing. Then I Measured resistance of the 2 prongs coming out of the egr. When the car was hot the resistance was 12 ohms and when it was cold it was 8 Ohms . The book indicates that the PTC should read 400-600 ohms room temperature. If there is a PTC where is it?? What other sensors might I have to replace??