Transmission Fluid Pressure Switch (TFP) Assembly

Fluid Pressure Switch Assembly:

Electronic Component Location Views:

PURPOSE
The fluid pressure switch assembly is used by the PCM to sense what gear range has been selected.

OPERATION
The fluid pressure switch assembly is located on the valve body and consists of five pressure switches, (2 normally closed and 3 normally open), and the transmission fluid temperature sensor combined into one unit. The PCM applies system voltage on three separate wires. These three circuits are either grounded or open, depending on which gear range has been selected and what combination of the five switches have pressure applied to them. With the engine "OFF" P/N will be indicated.

There are two possible combinations of the switches within the fluid pressure switch assembly that do not represent an actual gear range. If either of these combinations are detected by the PCM for 2 seconds on gasoline engines or 1.5 seconds or diesel engines, DTC 28 will set. DTC 28 will not set if a valid gear range combination appears at the wrong time.

While DTC 28 is present, the PCM will default to the following actions:

- Drive 4 for shift pattern control.
- Harsh shifts.
- Inhibit fourth gear when in Hot Mode.
Inhibit TCC operation.

If the fluid pressure switch assembly resumes normal functioning, the transmission will resume normal operation after the next ignition cycle.

PRNDL SELECT
This value represents the decoded sequence of the fluid pressure switch assembly to determine the manual valve position. The manual valve position is used to control line pressure, TCC, and shift solenoid operation.

A/B/C RANGE
These values represent the three fluid pressure switch assembly lines. These lines are normally high and are taken low. The sequence of these lines is decoded by the PCM to determine the appropriate gear range.