Ecu Self-Diagnostic Function; Troubleshooting Method - Yamaha MTN850-A 2017 Service Manual

EAS30505

ECU SELF-DIAGNOSTIC FUNCTION

The ECU is equipped with a self-diagnostic function in order to ensure that the fuel injection system is
operating normally. If this function detects a malfunction in the system, it immediately operates the en-
gine 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
number is stored in the memory of the ECU.
Checking the engine trouble warning light
The engine trouble warning light comes on for around 2 seconds after the main switch has been set to
"ON". If the warning light does not come on, the warning light (LED) may be defective.
ECU detects an abnormal signal from a sensor
If the ECU detects an abnormal signal from a sensor while the vehicle is being driven, the ECU illumi-
nates the engine trouble warning light and provides the engine with alternate operating instructions that
are appropriate for the type of malfunction.
When an abnormal signal is received from a sensor, the ECU processes the specified values that are
programmed for each sensor in order to provide the engine with alternate operating instructions that
enable the engine to continue operating or stop operating, depending on the conditions.
EAS30506

TROUBLESHOOTING METHOD

The engine operation is not normal and the engine trouble warning light comes on.
1. Check:
• Fault code number
▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼
a. Check the fault code numbers that have a condition of "Detected" using the Yamaha diagnostic tool.
b. Identify the faulty system with the fault code number.
c. Identify the probable cause of the malfunction.
▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲
2. Check and repair the probable cause of the malfunction.
Fault code No.
Check and repair. Refer to "TROUBLESHOOTING
DETAILS (FAULT CODE)" on page 8-37.
Monitor the operation of the sensors and actuators in
the diagnostic mode. Refer to "TROUBLESHOOT-
ING DETAILS (FAULT CODE)" on page 8-37 and
"SELF-DIAGNOSTIC FUNCTION AND DIAGNOS-
TIC CODE TABLE" on page 9-5.
3. Perform the reinstatement action for the fuel injection system.
Refer to "Confirmation of service completion" in the appropriate table in "TROUBLESHOOTING DE-
TAILS (FAULT CODE)" on page 8-37.
TIP
• If another fault code number is displayed, repeat steps (1) to (3) until no fault code number is dis-
played.
• Turning the main switch to "OFF" will not erase the malfunction history.
The engine operation is not normal, but the engine trouble warning light does not come on.
1. Check the operation of the following sensors and actuators in the diagnostic mode. Refer to "DIAG-
NOSTIC CODE: SENSOR OPERATION TABLE" on page 9-13 and "DIAGNOSTIC CODE: ACTU-
ATOR OPERATION TABLE" on page 9-16.
FUEL INJECTION SYSTEM
No fault code No.
Check and repair.
8-35