Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSBUICK1991CENTURY L4-151 2.5L VIN R TBIREPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTCOMPUTERS AND CONTROL SYSTEMSTRANSMISSION POSITION SENSOR/SWITCHTESTING AND INSPECTION
1991 Buick Century L4-151 2.5L VIN R TBI
Transmission Position Sensor/Switch: Testing and Inspection
1991 Buick Century L4-151 2.5L VIN R TBISECTION Testing and Inspection
Chart C-1A:
Wiring Diagram For P/N Switch:
CIRCUIT DESCRIPTION:
The PARK/NEUTRAL switch contacts are closed to ground in park or neutral and open in drive ranges. The ECM supplies ignition voltage through a current limiting resistor to circuit 434, and senses a closed switch when the voltage on circuit 434 drops to less than one volt. The ECM uses the P/N signal as one of the inputs to control idle air and vehicle speed sensor diagnostics.
TEST DESCRIPTION: The numbers below refer to circled numbers on the diagnostic chart.
1. Checks for a closed switch to ground in the PARK position. Different makes of "Scan" tools will read PARK/NEUTRAL differently. Refer to operators manual for type of display used for a specific tool.
2. Checks for an open switch in drive range.
3. Be sure the "Scan" tool indicates drive even while wiggling the shifter to test for an intermittent or misadjusted switch in drive.
RENDER: 1.0x
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.