Powertrain Controls - ECM/PCM

DTC 28 Transmission Range Switch Error:

Transmission Range Switch Wiring Schematic:

Circuit Description:
The transaxle range switch is a multiple signal switch that sends gear selector position information to the PCM. The PCM can decode what gear has been selected from a table. This is important to maintain idle quality when shifting for "Park" to "Drive," as well as for maintaining correct TCC engagement points.

DTC 28 Will Set When: The PCM indicates an incorrect combination of lows and highs from the transaxle range switch input for more than 10 seconds.

Action Taken (PCM will default to): When a DTC 28 is present, the PCM will default the transaxle to 3rd gear, until a correct combination is indicated by the PCM. Therefore, some gear select positions may not be possible until the fault is repaired.

DTC 28 Will Clear When: A current DTC 28 will clear after each ignition key cycle. A History DTC 28 will clear after 50 consecutive ignition key cycles without a current DTC 28 being stored.

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

1. This step check for proper operation of the transmission range switch.
2. This test checks for an open or grounded or shorted to B+ circuit.

Diagnostic Aids: An intermittent may be caused by a poor connection, chaffed wire insulation or a wire broken inside the insulation.

Check for:

^ Poor connection or damaged harness. Inspect PCM harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.
^ Intermittent test. Monitor a Tech 1 while moving related connectors and wiring harness. If the failure is induced, the scan data will change from low to high or high to low. This may help to isolate the location of the malfunction.