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Code B127:

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 PCM/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"= ground, "1"= not grounded. 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 PCM/ECM in a similar manner using one discrete input. This can be seen using PCM/ECM input "EI72" where 11 "HI" or 10 "LO" represent the voltage level of input terminal.

Code B127 sets when:

BCM gear selector switch input indicates P/N but PCM/ECM input does not.
BCM gear selector switch input indicates not P/N but PCM/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 Indicator Fault" and IPC "PRND321" display will box (Digital Cluster only) and back up lamps and memory seats are disabled.


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

1. Checks BCM inputs when only decoder A and parity circuit are pulled low.

2. Checks BCM inputs when only decoder B and C inputs are pulled low. This will complete high/low check of all 4 BCM inputs.

3. This step is to check for gear selector switch problems in other gear ranges.

4. Checks to see if code is due to discrepancy between PCM/ECM P/N and BCM PRND321 inputs.

NOTES ON INTERMITTENTS:

Manipulate related BCM and PCM/ECM wiring in each gear range while looking for a change in BD41 or ED72. Also check terminals for good contact at BCM, PCM/ECM and PRND321. If good contact and code B127 continues to set, then replace BCM.