P1120
CautionEngine Coolant Temperature (ECT) Sensor Circuit Intermittent High Voltage/IAT - B Circuit High Input
Is it safe to drive?
🔵 Do not use this page as drive-clearance. Monitor the alert and arrange service if it returns.
What does P1120 mean?
P-code P1120 means "Engine Coolant Temperature (ECT) Sensor Circuit Intermittent High Voltage/IAT - B Circuit High Input". It is a manufacturer-specific diagnostic trouble code (DTC) in the HVAC / climate control. The sensor or circuit is reading a voltage or signal value above its expected maximum range for the engine coolant temperature (ect) sensor circuit intermittent high voltage/iat - b circuit high input. 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
- Sensor reference voltage (V_Ref) line shorted to a higher voltage
- Faulty sensor outputting a signal above its calibrated range
- Corroded connector causing erratic high-voltage readings
- Control module failure misinterpreting the sensor signal
Recommended Actions
- 1 Note the alert and schedule a diagnostic appointment when convenient
- 2 Scan for all DTCs with an OBD-II scanner — note any related codes stored alongside P1120
- 3 Check the sensor reference voltage (should be ~5V) and signal output with a multimeter
- 4 Clean or replace the sensor connector — corrosion is a common cause of out-of-range voltage readings
- 5 Clear the DTC, road-test the vehicle, and re-scan to confirm whether the fault returns
- 6 If the fault persists after inspection and clearing, consult an EV-certified technician for component replacement