Inverter Coolant Temp Sensor Out of Range
Code C1774 indicates that the hybrid inverter ECU has detected an inverter coolant temperature sensor signal outside the allowable calibration range (voltage too high or low). This sensor is critical for thermal management of the inverter and motor-generator; an incorrect reading can lead to overheating of high-voltage components or a protection strategy that limits vehicle power.
1. Commonly Affected Makes
2. Most Common Causes
- Faulty inverter coolant temperature sensor (open or short circuit)
- Damaged, corroded, or shorted wiring or connector to the sensor
- Low coolant level or air pockets in the inverter cooling circuit
- Internal failure of the inverter ECU (Hybrid Vehicle Control ECU / Inverter ECU)
- Stuck thermostat in the inverter cooling circuit
3. Symptoms You Will Notice
- Check engine or hybrid system warning light illuminated
- Reduced vehicle power or limp mode
- Possible overheating of inverter components
4. Step-by-Step Diagnosis
Scan for additional codes and check freeze frame data
Inspect coolant level and condition in the inverter reservoir
Test sensor resistance and compare to specifications
Check wiring and connectors for damage, corrosion, or shorts
If sensor and wiring are OK, suspect inverter ECU failure
5. Frequently Asked Questions
Is it safe to drive?▼
No, driving with this code can lead to inverter overheating and potential damage to high-voltage components. Have the vehicle towed to a repair shop.
How much does it cost to fix?▼
Repair costs typically range from $200 to $800, depending on whether the sensor, wiring, or ECU needs replacement.