What tests can I make on a flame sensor for a white - rodgers 50A50-230 controller?

You have to have a meter that reads milivolts
First disconnect wire from flame sensor
Second put test leads between flame sensor (neg. to flame sensor pos. to wire)
Third turn on furnace and take reading

You should have 2-4 milivots if reading is low clean flame sensor with steelwhool or green scotch brite pad