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 MANUALSCHEVROLET1991R 30 P/U 2WD V8-350 5.7LREPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTCOMPUTERS AND CONTROL SYSTEMSENGINE CONTROL MODULETESTING AND INSPECTIONPOWERTRAIN CONTROL MODULE (PCM) TESTS - TBIPRESSURE SWITCH MANIFOLD CHECK
1991 Chevrolet R 30 P/U 2WD V8-350 5.7L
Pressure Switch Manifold Check
1991 Chevrolet R 30 P/U 2WD V8-350 5.7LSECTION Pressure Switch Manifold Check
Pressure Switch Manifold Check Procedure:
Wiring Diagram For Pressure Switch Manifold Check Procedure:
PRESSURE SWITCH MANIFOLD CHECK
CIRCUIT DESCRIPTION:
The Pressure Switch Manifold (PSM) is actually five pressure switches combined into one unit and mounted on the valve body. The PCM supplies battery voltage to the PSM on three separate wires. By grounding one or more these circuits through various combinations of the pressure switches inside the pressure switch manifold, the PCM detects what gear range has been selected by the vehicle operator.
TEST DESCRIPTION: Numbers below refer to circled numbers on the diagnostic chart.
1. This test compares the indicated range to the range actually selected.
2. This test checks for correct voltage from the PCM to the transmission pass through connector.
3. This final test will detect a short to ground in any one of the three PSM range circuits.
DIAGNOSTIC AIDS:
Code 28 will set if the PCM detects one of two illegal PSM combinations. See chart for various combinations. Be sure to check pass thru connector for good contact.
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.