Theory Of Operation

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The C1 through C4 (T41, T42, T3, and T1) signal circuits communicate the shift lever position to the Powertrain Control Module (PCM). Each circuit is terminated at the transmission with a switch. Each switch can be either open or closed, depending on the shift lever position. The PCM can decode this information and determine the shift lever position. Each shift lever position has a certain combination of switch positions (open or closed), this is called a PRNDL code. There are four switches, therefore: there are many possible combinations of open and closed switches (codes). However, there are only nine valid codes (eight for AutoStick), one for each gear position and three recognized between gear (transition) codes. Any other switch combinations should never occur, these are called invalid codes. The following chart shows the normal switch states for each shift lever position.