Engine Temperature Light Monitor Failure
Your engine's temperature monitoring system isn't working properly, like a broken thermometer that can't tell if water is hot or cold. The ECU can't verify that the coolant temperature sensor is functioning correctly during self-tests.
The ECU monitors the coolant temperature sensor (CTS) signal during engine startup and operation to ensure it's responding correctly within expected ranges. The sensor should show a gradual temperature change as the engine warms up. If the signal stays static, spikes unexpectedly, or fails to respond to actual temperature changes, the monitor fails.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| CTS Signal Voltage | 0.2-4.8V (varies with temperature) | Static voltage, no response, or out-of-range values |
| Temperature Rise Rate | Gradual increase from cold to operating temperature | No change or implausible rate during warm-up cycle |
Code P1374 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, P1374 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.