Toyota PT546-00140, Troubleshooting Manual

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20 ASL ASL ineffective (sound level will not increase).
Is the ASL setting OFF?
Change the ASL setting LOW or
higher.
Is the vehicle harness connected to the
head unit properly?
Connect the vehicle harnesses to
the head unit properly.
Temporarily install another head unit.
Is the function OK?
Head unit faulty.
Fault in the speed pulse signal line.
Check the speed pulse oscillation on the
signal wire.
Yes
No
No
No
Yes
Yes