Transmission Control System

CODE NUMBER
Scan tool: 21
General scan tool: P1781

CODE NAME
Pressure switch circuit: OD

CODE DESCRIPTION
Technical Description
The Transmission system uses pressure switch to monitor the fluid pressure in the OD clutch circuit. The pressure switch is continuously monitored for the correct states in each gear.
(P, R, N, 1st, 2nd, 3rd: Open/4th: close.)

Check Area
Whenever the engine is running.
- Engine speed must be greater than 500 r/min
- A shift must not be in progress, and there must be more than 2.0 seconds since start-up

Set Conditions
This code is set within 4 seconds if the OD pressure switch is open or closed at the wrong time in a given gear.

Transmission Effects:
- 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.

PROBABLE CAUSE
- 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
- Loose valve body bolts
- Plugged filter-internal transmission or torque converter failure
- Defective TCM





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