For 1988 through 1991 models and 1992 models with AOD transmission, to check the operation of the neutral start switch, apply the parking brake and attempt to start the engine in each position of the selector lever; the engine should only start in Park and Neutral. If it starts in any other position, adjust the shift linkage and retest. If the engine still starts in any position other than Park or Neutral, replace the switch. To replace the switch, disconnect the cable from the negative battery terminal, place the shift lever in Low, and apply the parking brake. Raise the vehicle and secure it on jackstands, then unplug the electrical connector from the neutral start switch. Carefully remove the switch and O-ring, install the new switch and O-ring, and tighten it. Reinstall the electrical connector and reconnect the negative battery cable. Verify that the engine starts only when in Park or Neutral. For 1992 models with AODE transmission and all 1993 and later models, note that the AODE and 4R70W transmissions do not have a neutral switch; this function is incorporated into an information sensor known as the Manual Lever Position (MLP) sensor or, for 1995 and later models, the Transmission Range (TR) sensor. For adjustment details, consult the relevant information.