BCM CODE B127 - PRND321 SENSOR
The PRND321 switch is a multi-signal switch sending information relative to gear selector position to BCM and ECM. Switch is mounted on transaxle assembly. The switch assembly also contains neutral safety switch, back-up light switch, and provides park input to automatic door lock module (if equipped). The switch uses 4 discrete circuits to pull BCM terminal voltages low in various combinations to indicate each gear selection. Voltage level of each circuit is represented in BCM data code BD41 as "0" for low, "1" for high. The 4 digits displayed represent decoder "A", "B", "C" and "PARITY" inputs in sequence.
The PRND321 switch also provides park/neutral input to the ECM in a similar manner using one discrete input. This is seen using the ECM input EI74 where "HI" or "LO" represent voltage level of the input terminal.
Code B127 sets when BCM PRND321 input indicates park/neutral but ECM input does not, BCM PRND321 input does not indicate park/neutral but ECM input does, or decoder and parity inputs do not agree with possible combinations of "CORRECT VALUES" chart. If code B127 is set, CCDIC will display the "GEAR SELECT PROBLEM" warning and Instrument Panel Cluster (IPC) will flash "PRND321" display.
Note. Test numbers refer to test numbers on diagnostic chart.
- 1) Checks BCM inputs when only decoder "A" and "PARITY" circuit are pulled low.
- 2) Checks BCM inputs only when decoder "B" and "C" inputs are pulled low. This will complete voltage check of all 4 BCM inputs.
- 3) Checks for a PRND321 switch problem in other gear ranges.
- 4) Checks if code is due to discrepancy between ECM and BCM inputs.
Manipulate related BCM and ECM wiring in each gear range while observing BD41 or EI74 values. If a failure is induced, values will change indicating an open or short to ground. Ensure good terminal connections exist at BCM, ECM and PRND321 switch. If terminal contacts are good and code B127 continues to set, replace BCM.
Code B127 Schematic, PRND321 Sensor (1 Of 2). Scheme 62
Code B127 Flow Chart, PRND321 Sensor (1 Of 2). Scheme 63
Note. Do not attempt to diagnose this code unless owner complaint is of "Gear Selector Fault" message on the DIC, a "Boxed" PRND321 display on the IPC, or improper gear selection display.
Code B127 Flow Chart, PRND321 Sensor. Scheme 64
- 5) Checks for short to ground in PRND321 to BCM circuit(s).
- 6) Checks for open in PRND321 to BCM circuit(s).
- 7) Circuit shorted to ground will result in a "0" display for the circuit.
- 8) Checks for open PRND321 sensor ground.
- 9) Open circuit will result in a "1" display for the circuit.
