Code 28, Fluid Pressure Switch Assembly Fault: Notes

The 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 the pressure switches inside the fluid pressure switch assembly, the PCM detects what gear range has been selected by the vehicle operator while idling.

With engine off, PARK/NEUTRAL will be indicated. 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 possibly no 4th gear (if in hot mode) will occur.

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-thru connector.
3. This test will detect a short to ground in any one of the 3 fluid pressure switch assembly range circuits.