Rob3rto
New Member
Hi everyone,
I have a Yamaha FZ6N, 2005, and I am currently trying to diagnose a strange running problem together with a persistent fault code 46.
The bike starts and runs normally when cold, but as it gets warm the idle becomes unstable, drops progressively (sometimes to around 600–700 rpm) and the engine can stall. After cooling down, it starts and runs again.
The thing that really caught my attention is the diagnostic code D09.
According to the service manual, D09 is fuel system voltage / battery voltage, and it should normally show approximately the actual battery voltage (~12 V with the engine stop switch ON).
However, on my bike:
Engine stop switch OFF → D09 = 0
Engine stop switch ON → D09 immediately goes to 18.6 V
It stays fixed at 18.6 V
Actual battery voltage at the same time is around 12.0–12.5 V
Fuel pump voltage is around 11.8 V
ECU red/white power supply is around 12.15–12.5 V
Injector supply voltage is approximately the same as the battery voltage
Coil supply voltage is also approximately the same as battery voltage
So I definitely do NOT have 18.6 V physically measured anywhere on the bike.
I have also checked the charging system:
Battery at rest: ~12.5 V
Engine idling: ~13.0 V
At 5000 rpm: ~14.0 V
Charging voltage remains approximately the same even when the engine is hot.
I also tested the ignition coils through diagnostic mode:
D30 – coils #1/#4: 5 sparks generated
D31 – coils #2/#3: 5 sparks generated
Both sides behave approximately the same.
During the test, battery voltage was around 12.25 V
Coil supply was around 12.16 V
I have also checked the injector voltage:
Around 1000 rpm: 12.4 V
When the engine drops to 600–700 rpm: around 11.7–11.8 V
Battery voltage measured at the same time is essentially the same, so there doesn't seem to be a significant voltage drop to the injectors.
The strange part is also the fault code 46.
Code 46 appears immediately when I turn the ignition ON. It does NOT appear only after starting the engine or after the engine gets hot. It is already there on the meter/cluster as soon as the ignition is switched on.
I have checked the wiring and connectors related to the FI system many times, including the ECU connector, FI relay/starting circuit cut-off relay, fuel pump and injector wiring. I also inspected the pins and connectors for loose or pushed-back terminals.
The FI relay is marked:
5VK-81950-30
G8R-30Y-V3
I have also checked the power supply circuits and measured the relevant voltages directly rather than relying only on the diagnostic display.
Another thing that makes me suspicious of the ECU is that the ECU housing/sealing around the main connector looks damaged/cracked, and there is visible evidence around the connector area that makes me wonder whether moisture/corrosion or an internal ECU problem could be involved.
At this point, the thing I cannot explain is:
Why does D09 show exactly 18.6 V when the actual battery voltage is only ~12 V, and why does it remain fixed at 18.6 V?
Could a faulty ECU, ECU ground, internal voltage sensing circuit, or another wiring issue cause D09 to display 18.6 V even though the actual supply voltage is normal?
I am planning to check the ECU grounds next using a voltage-drop test, rather than just checking continuity.
For reference, the service manual states that:
D09 = fuel system voltage (battery voltage), normally approximately 12.0 V
Fault code 46 = FI system power supply is not normal
So I would really appreciate any input from someone who has seen D09 stuck at 18.6 V on an FZ6.
Has anyone experienced this before? Could 18.6 V on D09 be an ECU/ECU ground/internal ECU issue, or is there something specific in the FZ6 wiring that I should check?
Thanks!
I have a Yamaha FZ6N, 2005, and I am currently trying to diagnose a strange running problem together with a persistent fault code 46.
The bike starts and runs normally when cold, but as it gets warm the idle becomes unstable, drops progressively (sometimes to around 600–700 rpm) and the engine can stall. After cooling down, it starts and runs again.
The thing that really caught my attention is the diagnostic code D09.
According to the service manual, D09 is fuel system voltage / battery voltage, and it should normally show approximately the actual battery voltage (~12 V with the engine stop switch ON).
However, on my bike:
Engine stop switch OFF → D09 = 0
Engine stop switch ON → D09 immediately goes to 18.6 V
It stays fixed at 18.6 V
Actual battery voltage at the same time is around 12.0–12.5 V
Fuel pump voltage is around 11.8 V
ECU red/white power supply is around 12.15–12.5 V
Injector supply voltage is approximately the same as the battery voltage
Coil supply voltage is also approximately the same as battery voltage
So I definitely do NOT have 18.6 V physically measured anywhere on the bike.
I have also checked the charging system:
Battery at rest: ~12.5 V
Engine idling: ~13.0 V
At 5000 rpm: ~14.0 V
Charging voltage remains approximately the same even when the engine is hot.
I also tested the ignition coils through diagnostic mode:
D30 – coils #1/#4: 5 sparks generated
D31 – coils #2/#3: 5 sparks generated
Both sides behave approximately the same.
During the test, battery voltage was around 12.25 V
Coil supply was around 12.16 V
I have also checked the injector voltage:
Around 1000 rpm: 12.4 V
When the engine drops to 600–700 rpm: around 11.7–11.8 V
Battery voltage measured at the same time is essentially the same, so there doesn't seem to be a significant voltage drop to the injectors.
The strange part is also the fault code 46.
Code 46 appears immediately when I turn the ignition ON. It does NOT appear only after starting the engine or after the engine gets hot. It is already there on the meter/cluster as soon as the ignition is switched on.
I have checked the wiring and connectors related to the FI system many times, including the ECU connector, FI relay/starting circuit cut-off relay, fuel pump and injector wiring. I also inspected the pins and connectors for loose or pushed-back terminals.
The FI relay is marked:
5VK-81950-30
G8R-30Y-V3
I have also checked the power supply circuits and measured the relevant voltages directly rather than relying only on the diagnostic display.
Another thing that makes me suspicious of the ECU is that the ECU housing/sealing around the main connector looks damaged/cracked, and there is visible evidence around the connector area that makes me wonder whether moisture/corrosion or an internal ECU problem could be involved.
At this point, the thing I cannot explain is:
Why does D09 show exactly 18.6 V when the actual battery voltage is only ~12 V, and why does it remain fixed at 18.6 V?
Could a faulty ECU, ECU ground, internal voltage sensing circuit, or another wiring issue cause D09 to display 18.6 V even though the actual supply voltage is normal?
I am planning to check the ECU grounds next using a voltage-drop test, rather than just checking continuity.
For reference, the service manual states that:
D09 = fuel system voltage (battery voltage), normally approximately 12.0 V
Fault code 46 = FI system power supply is not normal
So I would really appreciate any input from someone who has seen D09 stuck at 18.6 V on an FZ6.
Has anyone experienced this before? Could 18.6 V on D09 be an ECU/ECU ground/internal ECU issue, or is there something specific in the FZ6 wiring that I should check?
Thanks!
