Why after replacing speed sensor why does my speedometer still go haywire?

Question

I replaced vss and the speedometer went back to normal, I also replaced evap purge valve, and gas mileage went back to normal. But 30 minutes later the speedometer went haywire, and had mileage started dropping again. Why is this?

Answer 1

P0502 Vehicle speed sensor low input

P0496 EVAP system flow during non purge

Poor mating connection the type of speed sensor that the Cadillac uses is a AC generator type its produces a signal frequency. If the signal voltage is shorting together  it can do this