Engine Coolant Sensor intermittent/ECT Sensor Intermittent
Your engine's coolant temperature sensor is sending inconsistent signals to the computer, like a flickering light switch. The ECU can't reliably read how hot the coolant is, which confuses engine performance and emissions control.
The ECM monitors the Engine Coolant Temperature (ECT) sensor voltage signal, which should vary smoothly between 0.2V (hot) and 4.8V (cold) as coolant temperature changes. An intermittent fault occurs when the signal drops out, spikes erratically, or becomes inconsistent, preventing the ECU from calculating proper fuel trim and ignition timing.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| ECT Sensor Voltage | 0.2V to 4.8V (smooth variation) | Signal dropout, spikes, or erratic changes |
| Coolant Temperature Reading | -40°C to 125°C continuous | Jumps >10°C in short time or signal loss |
Code P1122 is a moderate fault. You can generally drive to a workshop, but avoid long trips or high-load driving (motorway, uphill towing) until it is diagnosed. If the code keeps returning after clearing, or if you notice the symptoms listed above worsening, do not delay professional diagnosis. Many moderate codes have multiple possible root causes — a mechanic with live OBD data can identify the exact fault more efficiently than part-by-part trial and error.
Once the fault is repaired, P1122 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.
The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.