Part 3 of 3

Code B127 (Part 3 of 3):

PRND321 Sensor Circuit:

DESCRIPTION:

The PRND321 switch is mounted on the transaxle assembly. It is a multi-signal switch sending information relative to gear selector position to the BCM and ECM. The PRND321 switch assembly also contains the neutral safety (start) switch and back-up light switch, and provides park input to the automatic door lock module (if equipped). The PRND321 switch uses 4 discrete circuits to pull 4 BCM terminal voltages low in various combinations to indicate each gear range. The voltage level of each of the circuits is represented in BCM data "BD41" as "O"= low, "1"= high. The 4 digits displayed represent decoder A, B, C and parity inputs in sequence.

The gear selector switch also provides park/neutral input to the ECM in a similar manner using one discrete input. This can be seen using ECM input "EI74" where "HI" or "LO" represent the voltage level of input terminal.

Code B127 sets when:

BCM gear selector switch input indicates P/N but ECM input does not.
BCM gear selector switch input indicates not P/N but ECM input does.
Decoder and parity inputs do not agree with possible combinations (per "BD41" value chart).

If code B127 is set, the DIC will display the warning "Gear Select Problem" and IPC "PRND321" display will flash.


TEST DESCRIPTION: The numbers below refer to circled numbers on the diagnostic chart.

10. The snap data value of BD41 will be the value that the BCM saw when the code set. From this, we determine whether this value is valid. If it is a valid value, then the ECM park/neutral input must be incorrect to set the code.

11. If the snap data value of BD41 is invalid, then we must determine which of the digits are invalid. If all digits read one, then the PRNDL ground is open. If only one digit is incorrect, that circuit, either in the switch or in the harness, was shorted or open when the code set.