Toro 30581 Groundsmaster 580-D Operator's Manual page 28

Indications that this is the cause of the problem include:
Flashing green diagnostic light
Diagnostic ACE will illuminate the "output fail" LED.
Diagnostic ACE will flash which output failed.
Machine will not respond to ignition key inputs.
The above indicates an ECU problem, contact your local
Authorized Toro Distributor for assistance.
If each output switch is in the correct position and
functioning correctly, but the output LED's are not
correctly illuminated, this indicates an ECU problem. If this
occurs, contact your Toro Distributor for assistance.
Important
The Diagnostic ACE display should not be
left connected to the machine. It is not designed to
withstand the environment of the machine's every day use.
When done using Diagnostic ACE, disconnect it from the
machine and reconnect loopback connector to harness
connector. Machine will not operate without loopback
connector installed on harness. Store Diagnostic ACE in
dry, secure location in shop, not on machine.
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