Subaru Legacy 2004 Service Manual page 2587

Diagnostic Procedure with Diagnostic Trouble Code (DTC)
AUTOMATIC TRANSMISSION (DIAGNOSTICS)
Step
11 CHECK ABSCM&H/U.
1) Turn the ignition switch to OFF.
2) Connect all the connectors.
3) Erase the memory.
4) Perform the inspection mode.
5) Read the DTC.
12 CHECK OTHER DTC DETECTION.
Check
Is the same DTC displayed?
Is any other DTC displayed?
5AT(diag)-128
Yes
Replace the TCM. Go to step 12.
<Ref. to 5AT-61,
Transmission Con-
trol Module
(TCM).>
Perform the diag- Temporary poor
nosis according to contact occurs.
DTC.
No