P028

DTC PO28: Part 1 Of 2:

DTC PO28: Part 2 Of 2:

Transaxle Range Switch Circuit:

CIRCUIT DESCRIPTION
The Powertrain Control Module (PCM) checks for illegal transaxle pressure switch inputs 000 and 010 (refer to the input chart located in the electrical schematic for pressure switch combinations) in addition to any of the following three failure conditions:

1. Transaxle range switch indicating not in P/N but the transaxle pressure switch input to the PCM indicating P/N (101) with a valid drive transaxle gear ratio (3.11 or less).
2. Transaxle pressure switch input to the PCM indicating REV (100) with a gear ratio not within recognized reverse gear ratio range (gear ratio less than or equal to 2.02 or gear ratio greater than or equal to 2.23).
3. Transaxle pressure switch input to the PCM indicating D1 (110), D2 (111), D3 (011), or D4 (001) with a reverse gear ratio (gear ratio between 2.02 to 2.23).

If any of the above conditions are met for 5 seconds, Code P028 will set for the entire ignition cycle.

TEST CONDITION # 1
Engine running.

FAILURE CONDITION # 1
1. An illegal transaxle pressure switch value (000 or 010) for 5 seconds.

TEST CONDITIONS # 2, # 3, and # 4
1. Codes P021, P022, P024, P056, P075, P086 and P091 not set.
2. Engine running.
3. Vehicle speed 7 mph or greater.
4. Throttle position 15.70 or greater.

FAILURE CONDITIONS # 2, # 3, and # 4
1. Transaxle range switch indicating not in PARK/NEUTRAL but transaxle pressure switch value 101 (P/N) with a gear ratio of 3.11 or less for 5 seconds.
2. Transaxle pressure switch value 100 (REV) with a gear ratio of 2.02 or less for 5 seconds.;
OR
Transaxle pressure switch value 100 (REV) with a gear ratio of 2.23 or greater for 5 seconds.
3. Transaxle pressure switch value 001 (D4), 011 (D3), 111 (D2), or 110 (D1) with a gear ratio of between 2.02 and 2.23 for 5 seconds.

ACTION TAKEN
1. PCM turns "ON" Malfunction Indicator Lamp (MIL) (Service Engine Soon).
2. The PCM will substitute the previous transaxle pressure switch value if it is consistent with the transaxle range switch. If transaxle pressure switch value is not consistent with the transaxle range switch, the PCM will substitute D4 for the transaxle pressure switch value if the transaxle range switch indicates "DRIVE/REVERSE" and P/N if the transaxle range switch indicates "PARK/NEUTRAL."
3. Code P028 will be for the entire ignition cycle.

NOTES ON FAULT TREE
(Part 1 of 2)
1. Checking PCM data PD71 for a failure that is present in all transaxle ranges. ("1" is an open in the circuit while "0" is a short to ground.)
2. Determining in which circuit the failure is present.
3. Checking if the PCM is receiving the correct voltage changing between 0 and 12 volts and not recognizing it.
4. If the voltage remains at 0 volt, there is a short to ground in the circuit while voltage remaining at 12 volts indicates an open in the circuit.
5. Checking if the short to ground is inside the transaxle or not.

(Part 2 of 2)
6. If PD71 matches the chart (refer to the input chart located in the electrical schematic for pressure switch combinations), the fault is intermittent. If PD71 does not match the chart, the transaxle range switch must be giving wrong readings.
7. Checking if the failure occurred while the vehicle was in reverse or not. If the gear ratio was between 2.02 and 2.23, the vehicle was in reverse when the failure occurred.
8. Checking P028 snapshot data PD71 to determine the exact transaxle pressure switch value that was present when the code set to determine which circuits are open or shorted to ground.