Subaru Legacy 2002 Service Manual page 1811

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)
Automatic Transmission (Diagnostics)
B: DTC 27 ATF TEMPERATURE SENSOR
S004521I11
DIAGNOSIS:
Input signal circuit of TCM to ATF temperature sensor is open or shorted.
TROUBLE SYMPTOM:
Excessive shift shock.
WIRING DIAGRAM:
S3M0626
AT-42