31 OD Hydraulic Pressure Switch

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. immediately after a shift into 1st, 2nd, or 3rd gear with the engine speed above 1000 RPM's, 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.

LIMP-IN:
YES

WHEN MONITORED/SET CONDITIONS:
In 1st, 2nd, or 3rd gear with the engine speed above 1000 RPM shortly after a shift and every minute thereafter. The following conditions must be met for a successful OBDII trip:
- The engine speed must be greater than 1000 RPM.
- The transmission must be warm or hot.
- The vehicle must be driven in 1st gear continuously for 8 seconds, or in 2nd gear for 8 seconds and in 3rd gear continuously for 8 seconds.
- No MIL lamp trouble codes have occurred or recurred.

TRANSMISSION EFFECTS:
All model years and calibrations - relay open limp-in mode.

POSSIBLE CAUSES:
- Pressure switch sense circuit shorted to battery between TCM and solenoid pack
- Solenoid pack defective