Yamaha 2004 YP400, Service Manual, Page: 304 / 417

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FI
FUEL INJECTION SYSTEM
ECU’S SELF-DIAGNOSTIC FUNCTION
The ECU is equipped with a self-diagnostic function in order to ensure that the engine control sys-
tem is operating normally. If this function detects a malfunction in the system, it immediately oper-
ates the engine under substitute characteristics and illuminates the engine trouble warning light to
alert the rider that a malfunction has occurred in the system. Once a malfunction has been detected,
a fault code is stored in the memory of the ECU.
• To inform the rider that the fuel injection system is not functioning correctly, the engine trouble
warning light flashes when the start switch is being pushed to start the engine.
• If a malfunction is detected in the system by the self-diagnostic function, this mode provides an
appropriate substitute characteristic operation, and alerts the rider of the detected malfunction by
illuminating the engine trouble warning light.
• After the engine has been stopped, the lowest fault code number appears on the LCD meter.
Once a fault code has been displayed, it remains stored in the memory of the ECU until it is
deleted.
EAS00900
Engine trouble warning light indication and FI system operating condition
* The warning light flashes when any one of the conditions listed below is present and the start
switch is pushed.
12: Crankshaft position sensor
19: Broken or disconnected blue/yellow lead of
the ECU
30: Lean angle cut-off switch
(latch up detected)
33: Faulty ignition
39: Fuel injector
(open or short circuit)
41: Lean angle cut-off switch
(open or short circuit)
50: ECU internal malfunction
(memory check error)
Warning light
indication
ECU’s operation FI operation Vehicle operation
Flashing* Warning provided
when unable to start
engine Operation stopped Unable
Remains ON Malfunction detected Operated with substi-
tute characteristics in
accordance with the
description of the mal-
function Able/Unable depend-
ing on the self-diag-
nostic fault code