With 4L80E Automatic Transmission

DTC 28 Transmission Range (TR) Pressure Switch Assembly Fault:

Transmission Range (TR) Pressure Switch Assembly Circuit:

Transmission Range (TR) Expected Readings:

CIRCUIT DESCRIPTION
The Transmission Range (TR) switch assembly consists of five normally open pressure switches and is attached to the valve body. The Powertrain Control Module (PCM) supplies battery voltage to each range signal. 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. With ignition "ON" and engine "OFF," P/N will be indicated. When the transmission electrical connector is disconnected, the ground potential for the three range signals to the PCM will be removed, and with ignition "ON," D2 will be indicated.

DTC 28 WILL SET WHEN
Range signals "A" and "C" are both zero volts "ON" for 2 seconds.

ACTION TAKEN (PCM will default to)
Harsh shifts, drive 4 shift control. TCC will be inhibited, and if in hot mode, there will be no fourth gear. DTC 28 will be stored in the PCM memory but will not turn "ON" the Malfunction Indicator Lamp (MIL).

DTC 28 WILL CLEAR WHEN
The fault condition(s) no longer exist, and the ignition switch is cycled from "OFF" then "ON."

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. This test checks the indicated range signal to the manual valve position actually selected.
2. This test checks for correct voltage from the PCM to the transmission external connector.
3. This test checks for a short to ground from the PCM to the transmission external connector in any one of the three circuits.

DIAGNOSTIC AIDS
DTC 28 will set if the PCM detects one of two "Illegal" combinations.
Refer to accompanying chart for various A/B/C range combinations. Check all wiring connectors for proper terminal tension.