Hi jeffrey gutmore. Welcome to the forum. The two are not related. The purpose of the neutral safety switch is to prevent the starter from cranking the engine unless the transmission is in park or neutral. It will not start when it is in reverse or drive. When the switches fail, they usually cause a no-crank condition but in rare instances they could allow engine starting when in gear. They are also not monitored by the Engine Computer on most cars so they should not cause the Check Engine light to turn. It is more likely slippage in the clutch packs in the transmission caused the Check Engine light to turn on.
A possible exception might be if a lot of transmission fluid drained out while the switch was being replaced. Low fluid level could cause the symptoms you described. I have to look where the switch is located on your car. Ford used to put them inside the car so it would not affect anything on the transmission. Chrysler screws theirs into the case of the transmission but almost no fluid drains out when they are replaced.
Is it possible it was not the neutral safety switch that was replaced? There are other sensors and switches on the transmission that will set diagnostic fault codes and cause the Check Engine light to turn on.
Tuesday, June 15th, 2010 AT 7:15 PM