1, 2 and 3 Digit Codes: 21

Name of Code:
21-OD Pressure Switch Circuit

When Monitored:
Whenever the engine is running.

Set Condition:
This code is set if the OD pressure switch is open or closed at the wrong time in a given gear (see chart below).

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.

Transmission Effects:
- 96 MY V-1 calibration - relay open limp-in mode.
- 96 MY V-2 (default desensitization) and 97 MY - 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Shifter mis-positioned between OD & N (89-95 MY vehicles without TCM updates per TSB 18-24-95 (or later if 18-24-95 is superceded)
- Loose valve body bolts
- Plugged filter - internal transmission or torque converter failure
- Defective TCM