21 OD Pressure Switch Circuit

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THEORY OF OPERATION:
The Transmission system uses three pressure switches to monitor the fluid pressure in the L-R, 2-4, and OD clutch circuits. The pressure switches are continuously monitored for the correct states in each gear as shown below.





This code is set if the OD pressure switch is open or closed at the wrong time in a given gear.

LIMP-IN:
- YES (89-95 MODEL YEARS)
- NO (96-97 MODEL YEARS)

WHEN MONITORED/SET CONDITIONS:
Whenever the engine is running.
- Engine speed must be greater than 500 RPM
- A shift must not be in progress, and there must be more than 2.0 seconds since start-up
- No loss of prime test in progress, and a pressure switch mismatch
- The code sets within 4 seconds.

TRANSMISSION EFFECTS:
- 89-94 model year + 96 model year V-1 calibration - relay open "limp-in mode.
- 96 model year V-2 (default desensitization) and 97 model year - Normal operation will be experienced if no other fault codes are present. TCM will ignore the code. Limp-in condition will only occur if code 21 is present with a code 28.

POSSIBLE CAUSES:
- If code 35 is present, ignore code 21 and perform code 35 diagnostic procedures
- OD pressure switch sense circuit open or shorted to ground between TCM and solenoid pack
- OD pressure switch sense circuit shorted to battery
- Solenoid pack defective
- Shifter mispositioned between OD & N (89-95 model years vehicles without TCM updates per TSB 18-24-95 (or later if 18-24-95 is superseded)
- Loose valve body bolts
- Plugged filter - internal transmission or torque converter failure
- Defective TCM