One of the most frustrating moments in an Indian two-wheeler garage is replacing a faulty sensor with a brand-new genuine OEM part, starting the motorcycle, and seeing the yellow Check Engine (MIL) lamp continue to glow stubbornly on the console.
1 Why Does the MIL Stay ON After Sensor Replacement?
Unlike older carbureted bikes, BS6 vehicles use a microprocessor ECU that stores fault records inside non-volatile EEPROM memory. Replacing the sensor restores physical signal voltages, but the stored DTC flag remains active in memory until explicitly reset or cleared by the ECU's internal self-test algorithm.
2 Active vs Stored Historic DTCs
The sensor is actively outputting out-of-range signals right now. The MIL light stays constantly lit and cannot be erased until the hardware fault is fixed.
The fault occurred in the past (e.g., coupler disconnected during washing). The sensor is working now, but the ECU keeps the MIL on until cleared.
3 Solid MIL vs Flashing MIL Warning
- Solid Glowing Lamp: General emissions-related sensor defect (O2 sensor, EOT, TPS). Vehicle can be driven safely to the workshop in limp mode.
- Flashing / Blinking Lamp: Severe engine misfire (P0300) or bank angle sensor trip that risks melting the catalytic converter. Stop the engine immediately.
4 Honda & Hero Blink Codes Table
On scooters like Honda Activa 6G and Hero Splendor BS6 without an LCD scanner connected, the MIL light flashes diagnostic pulses:
| MIL Blinks | DTC Code | Component | Symptoms |
|---|---|---|---|
| 7 Blinks | P0117 / P0118 | EOT / ECT Sensor | Hard cold start, rich black smoke |
| 8 Blinks | P0122 / P0123 | TPS Sensor | Jerking on acceleration |
| 12 Blinks | P0201 | Fuel Injector | Cranks but won't start |
| 21 Blinks | P0130 / P0134 | O2 Lambda Sensor | High fuel consumption |
| 54 Blinks | P1505 | Bank Angle Sensor | Spark & fuel cut after tip-over |
5 Proper OBD-II Mode 04 Clear Workflow
- Fix or replace the damaged sensor or wiring.
- Connect scanner and turn motorcycle ignition ON (Kill switch ON, engine NOT running).
- Open VahanScan and tap “Clear DTCs (Mode 04)”.
- The app sends byte
04across CAN / K-Line. The ECU flushes fault memory and the MIL light turns OFF instantly. - Start the engine and idle for 2 minutes to verify the light remains extinguished.
6 3-Trip Drive Cycle Reset
If you do not have an OBD scanner on hand, the ECU will automatically extinguish the MIL light if it completes 3 consecutive driving warm-up cycles without detecting the fault again:
- Start cold engine and ride above 40 km/h for at least 10 minutes until engine oil exceeds 70°C.
- Turn engine off and let it cool completely down. Repeat 3 times.