Transmission Position Sensor/Switch: Testing and Inspection

Park/Neutral Switch Circuit Diagram:

CIRCUIT DESCRIPTION

The Park/Neutral (P/N) switch gets a 12 volt reference from the PCM, and the PCM monitors the circuit. When the switch is in the park or neutral position, it grounds the circuit, causing a drop in the circuit voltage. Low voltage in circuit 434 indicates the transmission is not in a drive gear. The PCM uses this information for the following:
^ Idle Air Control valve operation
^ Vehicle Speed Sensor diagnosis
^ EGR control
^ Torque Converter Clutch Control

NOTE: If circuit 434 indicates Park/Neutral while transmission is in a drive range (circuit 434 voltage low - switch grounded), the EGR system will not operate and engine may "PING" under load. If circuit 434 voltage remains high (circuit open) while transmission is in Park/Neutral, a drop in idle speed may be noticed when transmission is placed in a drive range.

TEST DESCRIPTION

Chart C-1A, Park/Neutral Switch Diagnosis:

Numbers below refer to circled numbers on diagnostic chart.

1. Checks for a closed switch to ground (shorted switch) in park position. Different makes of "SCAN tools display P/N differently. Refer to specific manufacturers instructions for correct display on your tool.
2. Determines if drive range indication while in Park/Neutral is due to faulty or misadjusted P/N switch.
3. To check for intermittent fault or misadjusted switch, wiggle shifter while observing "SCAN" tool display. Be sure "SCAN" tool indicates drive whenever transmission is in drive range.