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.
Code 28, Pressure Switch Manifold Fault: Notes
The Pressure Switch Manifold (PSM) is actually 5 pressure switches combined into one unit and mounted on the transmission valve body. The PCM/TCM supplies battery voltage to the PSM on 3 separate wires. By grounding one or more of these circuits through various combinations of the pressure switches inside the pressure switch manifold, the PCM/TCM detects what gear range has been selected by the vehicle operator.
- This test compares the indicated range to the range actually selected.
- This test checks for correct voltage from the PCM/TCM to the transmission pass-thru connector.
- This test will detect a short to ground in any one of the 3 PSM range circuits.
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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.
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