If your engine management light (EML) is on, or if the bike is running poorly, you can use the FI diagnostic tool to access "Diagnostic Mode" (dIAG). Here are the most common codes and what they test.
Diagnostic Codes (Sensor Data)
These codes allow you to check if a sensor is sending the correct signal to the ECU.
D01 (Throttle Position): Displays the throttle angle.
Target: 14–20 (Closed) to 97–107 (Fully Open).
D03 (Intake Air Pressure): Displays the air pressure in the intake. Crank the engine to see the value change.
D05 (Intake Air Temperature): Displays the temperature of the air entering the engine.
D07 (Speed Sensor): Check this by spinning the rear wheel; the value should increase.
D08 (Lean Angle Sensor): * Target: 0.4V–1.4V (Upright). If it reads over 3.8V, the bike thinks it has tipped over and will cut the engine.
D09 (Battery Voltage): Displays the current voltage being supplied to the ECU (should be ~12V).
D20/D21: Checks the Side Stand and Neutral switches. Toggle them to see the display change from "On" to "Off."
Actuation Tests (Component Testing)
In these modes, pressing the MODE button will force the ECU to trigger a specific component. Use this to find broken parts without taking the engine apart.
D30 (Ignition Coil): Pressing Mode will fire the spark plug 5 times. (Ensure the plug is grounded to the engine to see the spark).
D36 (Fuel Injector): Pressing Mode will pulse the injector 5 times. You should hear a distinct "clicking" sound.
D51 (Radiator Fan): Triggers the cooling fan relay to spin the fan.
D52 (Headlight Relay): Cycles the headlight on and off 5 times.
D54 (Fast Idle Solenoid): Triggers the air bypass valve; you should hear it clicking and see the engine light flash.
History & Reset Codes
D60: EEPROM fault display (00 means no fault).
D61: Displays the history of triggered fault codes (e.g., if the bike had a fault code 12 in the past).
D62: Used to clear the fault code history.
Yamaha YZF-R125 Engine Management "Blink" Codes
If you don’t have the FI Diagnostic Tool, you can still diagnose your bike by watching the Engine Management Light (EML). When the ignition is on, the light will blink in a specific sequence to tell you the fault code.
Long Blinks (1.5 sec): Represent the "tens" digit (e.g., 4 long blinks = 40).
Short Blinks (0.5 sec): Represent the "units" digit (e.g., 2 short blinks = 2).
Example: 1 long blink followed by 2 short blinks = Fault Code 12.
The Fault Code Chart
| Code | Component / Fault Description | Common Symptoms |
| 12 | Crankshaft Position Sensor | Engine cranks but won't start; no spark. |
| 13 | Intake Air Pressure Sensor (Open/Short) | Rough idling; poor throttle response. |
| 14 | Intake Air Pressure Sensor (Hose Clogged) | Stalling; erratic engine speeds. |
| 15 | Throttle Position Sensor (TPS) | Poor acceleration; bike "stutters" when revving. |
| 19 | Sidestand Switch | Engine cuts out when put into gear. |
| 21 | Coolant Temperature Sensor | Hard starting when cold; radiator fan issues. |
| 22 | Intake Air Temperature Sensor | Slight loss of power; poor fuel economy. |
| 30 | Lean Angle Sensor (Tip-Over) | Engine won't start (bike thinks it's on its side). |
| 33 | Ignition Coil (Primary Fault) | Misfiring or complete loss of spark. |
| 41 | Lean Angle Sensor (Internal Fault) | Engine won't start; EML stays on. |
| 42 | Speed Sensor / Neutral Switch | Speedometer reads 0; neutral light issues. |
| 43 | Fuel Pump Voltage | Fuel pump won't prime; engine starves for fuel. |
| 44 | EEPROM Error | ECU memory fault (often requires a reset). |
| 46 | Charging System Voltage | Battery not charging; lights dimming. |
| 50 | ECU Internal Fault | Critical engine failure; bike may enter "limp mode." |
How to Read Current Faults on the Dash
If your bike is a later model with a digital screen, you can often view the "Current" fault code directly:
Turn the Ignition OFF and set the Kill Switch to ON.
Hold down both Select + Reset buttons.
Turn the Ignition ON (continue holding buttons for ~8 seconds).
The screen will change to "dIAG".
Release and press Select + Reset again for 2 seconds to enter the menu.
Scroll to d61 to see the history of codes stored in the memory.
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