The Park/Neutral position switch blocks engine start when the car isn't in Park or Neutral; if the engine starts in any other gear, either adjust or replace this switch. After raising your car and putting jackstands under it, disconnect the electrical connector from the switch. Using an ohmmeter with the ignition key off, check if the switch inside the connector shows continuity across the right terminals - if not, attempt to adjust it back to working order and check again; replace the switch if it still doesn't work. To fix it, put the shift lever into Neutral, lift the car, and stand it on jackstands. Loosen the switch's bolt, match the groove up with the neutral basic line, hold the switch there, and tighten the bolt again. To replace the switch, pull the electrical plug away, remove the lock nut by hand, loosen the bolt holding the switch in place, and take out both the bolt and switch. You install back into place, fixing the switch and making sure its electrical connections work.