DTC 33 - P1789

Name of Code:
- P-1787(31) - OD Hydraulic Pressure Test Failure
- P-1788(32) 2-4 Hydraulic Pressure Test Failure
- P-1789(33) OD/2-4 Hydraulic Pressure Test Failure

When Monitored: In 1st, 2nd, or 3rd gear with engine speed above 1000 RPM shortly after a shift and every minute thereafter.

Set Condition: Immediately after a shift into 1st, 2nd, or 3rd gear, with engine speed above 1000 RPM, the TCM momentarily turns on element pressure to the 2-4 and/or OD clutch circuits to identify that the appropriate pressure switch closes. If the pressure switch does not close it is tested again. If the switch does not close the second time, the appropriate code is set.

Theory of Operation: The Transmission Control Module (TCM) tests the OD and 2-4 pressure switches when they are off (OD and 2-4 are tested in 1st gear, OD in 2nd gear, and 2-4 in 3rd gear). The test verifies that the switches are operational. The TCM verifies that the switch closes when the corresponding element is applied. If a switch fails to close, it is retested, If it fails the second test, the code is set.

Transmission Effects: The MIL illuminates and the transmission system defaults to Relay Open limp-in mode.

Possible Causes:
- Pressure switch sense circuit shorted to battery between TCM and solenoid pack.
- Low line pressure
- Solenoid Pack