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.
Fluid Pressure Switch Assembly Circuit Check: Notes
Fluid pressure switch assembly consists of a fluid temperature sensor and 5 pressure switches combined into one unit and mounted on the transmission valve body. The PCM supplies battery voltage to the fluid pressure switch on 3 separate wires. By grounding one or more of these circuits through various combinations of switches inside the fluid pressure switch assembly, the PCM detects what gear range has been selected by the vehicle operator.
If range signals "A" and "C" are zero volts, or all 3 signals are zero volts for 1.5 seconds on diesel engine or 2 seconds on gasoline engine, Code 28 will set. When Code 28 is set, harsh shifts, no TCC, and no 4th gear (if in hot mode) may occur.
- This test compares the indicated range to the range actually selected.
- This test checks for correct voltage from the PCM to the transmission pass-thru connector.
- This test will detect a short to ground in any one of the 3 fluid pressure switch assembly 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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