Pressure Switch Manifold (PSM)

4L80-E AUTOMATIC TRANSMISSION

Pressure Switch Manifold Circuit Diagnosis:

Pressure Switch Manifold:

Circuit Description:
The Pressure Switch Manifold (PSM) is actually five pressure switches combined into one unit and mounted on the valve body. The PCM supplies battery voltage to the PSM on three separate wires. By grounding one or more of these circuits through various combinations of the pressure switches inside the pressure switch manifold the PCM detects what gear range has been selected by the vehicle operator.

Test Description:
Numbers below refer to circled numbers on the diagnostic chart.

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 final test will detect a short to ground in any one of the PSM range circuits.

Diagnostic Aids:
Code 28 will set if the PCM detects one of two illegal PSM combinations.

See below for various combinations. Be sure the check pass-thru connector for good contact.

Expected Voltage Readings

A B C

Park 12 0 12
Reverse 0 0 12
Neutral 12 0 12
Forth 12 0 0
Third 12 12 0
Second 12 12 12
First 0 12 12
Illegal 0 12 0
Illegal 0 0 0