| Fault code No. | 21 |
| Symptom | Open or short circuit of coolant temperature sensor lead |
| Fail-safe action | Engine startup: Possible |
| Riding: Possible | |
| Diagnostic monitoring code No. | D:06 |
| Meter display | Displays the coolant temperature. |
| Checking method | Compare the actually measured coolant temperature with the meter display value. |
| Item/components and probable cause | Check or maintenance job | Sensor inspection procedure | |
| 1 | Connection of coolant temperature sensor coupler. Check the connection of the coupler is secure. Remove the coupler, and check each pin (for bending, wear, or locking). | Poor connection → Connect it securely, or repair/replace the wire harness. | Place the main switch to the ON position, and check the fault code indication. No fault code indicated. → Recovered. Fault code indicated. → Check the next step. |
| 2 | Connection of main harness ECU coupler. Check the connection of the coupler is secure. Remove the coupler, and check each pin (for bending, wear, or locking). | Poor connection → Connect it securely, or repair/replace the wire harness. | Place the main switch to the ON position, and check the fault code indication. No fault code indicated. → Recovered. Fault code indicated. → Check the next step. |
| 3 | Continuity of wire harness | Open or short circuit → Replace the wire harness Black/Blue-Black/Blue Green/White-Green/White | Place the main switch to the ON position, and check the fault code indication. No fault code indicated. → Recovered. Fault code indicated. → Check the next step. |
| 4 | Installation status of coolant temperature sensor | Check the mounting section for a loose or pinched mounting. Make sure that the mounting position is correct. | Place the main switch to the ON position, and check the fault code indication. No fault code indicated. → Recovered. Fault code indicated. → Check the next step. |
| 5 | Coolant temperature sensor malfunction | Check in the diagnostic mode (Code No. 06). During cold starting: A temperature close to the ambient temperature is indicated. Indication is incorrect. → Replace the coolant temperature sensor. | Place the main switch to the ON position, and check the fault code indication. No fault code indicated → Recovered. Fault code indicated. → Check the next step. |
| 6 | ECU malfunction | Replace the ECU. |
*Check the sensor only when the engine is cold.