C1781

What does C1781 mean?

C-code C1781 means "Engine Coolant Temperature Signal Missing/Fault". It is a manufacturer-specific diagnostic trouble code (DTC) in the chassis / braking. An abnormal temperature condition has been detected in the engine coolant temperature signal missing/fault — the system may be overheating or running too cold. This code can be monitored, but service is recommended to prevent escalation. This code applies to OBD-II compliant electric and hybrid vehicles.

Possible Causes

• Cooling system failure (low coolant, blocked radiator, or pump failure)
• Ambient temperature extremes affecting sensor calibration
• Faulty temperature sensor providing inaccurate readings
• Thermal management system component failure

Recommended Actions

1. 1 Note the alert and schedule a diagnostic appointment when convenient
2. 2 Scan for all DTCs with an OBD-II scanner — note any related codes stored alongside C1781
3. 3 Check coolant level, coolant flow, and cooling fan operation
4. 4 Inspect the temperature sensor and its wiring for damage or corrosion
5. 5 Clear the DTC, road-test the vehicle, and re-scan to confirm whether the fault returns
6. 6 If the fault persists after inspection and clearing, consult an EV-certified technician for component replacement

Related Chassis fault codes