Part 1 of 2

DTC P028:

Transaxle Pressure Switch Circuit:

CIRCUIT DESCRIPTION:
The PCM checks for illegal transaxle pressure switch inputs (000 & 010) 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 ear ratio range (gear ratio less than or equal to 2. 2 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. 2 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(S): #1
Engine running.

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

TEST CONDITION(S): #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 CONDITION(S): #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 .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" "SERVICE ENGINE SOON" MIL.
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:
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.

* SEE PART 2 OF 2 FOR NOTES 4 AND 5