Powertrain Controls - ECM/PCM

DTC 28 Chart (1 Of 3):

DTC 28 Chart (2 Of 3):

DTC 28 Chart (3 Of 3):

Transaxle Range Switch Circuit:

Range Combination Chart:

Transaxle Gear Ratio Chart:

CIRCUIT DESCRIPTION
The transaxle range pressure switch contains five normally open pressure switch assemblies mounted on the valve body. The PCM supplies battery voltage to each pressure switch. The pressure switch produces either an open or a ground for the three PCM signal lines, depending on which switches have pressure applied to them. The sequence of which switches are open and which switches are closed will be used by the PCM to determine actual manual valve position. The PCM compares the voltage values it receives to a transaxle range switch combination chart stored in system memory.

DTC 28 WILL SET WHEN
- DTC(s) 21, 22, 24, 56, 75, 86 or 91 are not set.
- Vehicle speed is greater that 7 mph.
- Throttle angle is greater than 15.7 degrees.
- All the above conditions and any one of the below conditions are present for 5 seconds or more.
- The PCM detects an illegal input from the transaxle range pressure switch.
OR
- P-N-P switch indicating not in P/N but transaxle range pressure switch is indicating (P/N) with a valid drive transaxle gear ratio of 3.11 or less.
OR
- Transaxle range pressure switch indicating (reverse) with a transaxle gear ratio not within the recognized range (between 2.01 and 2.24).
OR
- Transaxle range pressure switch indicating (D1), (D2), (D3), or (D4) with a transaxle gear ratio within the recognized reverse range (between 2.01 and 2.24).

ACTION TAKEN (PCM WILL DEFAULT TO)
- With a current DTC 28 set, the PCM will illuminate the Malfunction Indicator Lamp (MIL) (Service Engine Soon).
- The PCM will command a defaulted transaxle range pressure switch value based on the P-N-P switch position. If the P-N-P switch indicates R-OD21, the defaulted value will be (D4). The defaulted value will be (P/N) if P-N is indicated by the P-N-P switch.

DTC 28 WILL CLEAR WHEN
The fault no longer exists.

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

1. This test checks the function of the transaxle range switch.
2. This test checks to see which range signal has a fault.
3. This test checks to see if the PCM will recognize the change in voltage zero to 12 volts.
4. This test checks to see if there is an open or shorted CKT.
5. This test checks to see if the short is inside the transaxle.
6. This test rechecks the function of the transaxle range switch (possibly intermittent).
7. This test checks to make sure that the range signal wires are not shorted together.
8. This test checks for a poor connection or faulty PCM.
9. This test checks to see if DTC 28 can be reset.
10. This test checks the snapshot data stored at the time the fault was present, to determine when CKTs were "open or shorted".