Even in millivolt gas valves there are several configurations depending on manufacturer. Then there are gas valves like you seem to be talking about that are electronically lit by a spark. The spark ignitor doubles as the flame sensor and the ignition module reads the millivolts that travel back when the ignitor is heated by the flame. A very light cleaning with a green scotchbrite pad helps also removing and cleaning the entire pilot assembly to ensure it is grounded to the metal it attaches to. If I'm on the right track with the design you're talking about you should be looking for the voltage after ignition traveling to the gas valve. Is this an intermitant pilot or just burner ignition as difrferent tests are used to check out the various components?