Powertrain Controls - ECM/PCM

DTC 28 Fluid Pressure Switch Assembly Fault:

Fluid Pressure Switch Assembly Circuit:

Circuit Description:
The fluid pressure switch assembly consists of five pressure switches (2 normally closed and 3 normally open), and a fluid temperature sensor combined into one unit and mounted on the valve body. The PCM supplies battery voltage to each range signal on three separate wires. By grounding one or more of these circuits through various combinations of the pressure switches, the PCM detects what manual valve position has been selected by the vehicle operator while idling with the engine "OFF" P/N will be indicated. If range signals "A" and "C" are 0 volt, or all three signals are 0 volt for 1.5 seconds on the diesel engine, or 2 seconds on the gasoline engines, DTC 28 will set. When DTC 28 is set, harsh shifts, no TCC will occur, and no fourth gear if in hot mode.


Test Description:
Number(s) below refer to circled number(s) on the diagnostic chart.

1. This test checks the indicated range signal to the valve position signal actually selected.
2. This test checks for correct voltage from the PCM to the transmission pass-thru connector.
3. This test checks a short to ground in any one of the three valve position circuits.

Valid Combination Chart:

Diagnostic Aids:
DTC 28 will set if the PCM detects one of two "illegal" combinations.
Refer to accompanying chart for various combinations.
Check pass-thru connector for good contact.