Catalyst Temperature Sensor Failure
Your vehicle's catalyst temperature sensor isn't sending proper readings to the engine computer, like a broken thermometer that can't tell if your engine's catalytic converter is running hot enough. The ECU can't verify the converter is working efficiently to clean emissions.
The ECU monitors voltage output from the catalyst temperature sensor to verify the catalytic converter reaches and maintains optimal operating temperature (typically 400-900°C). The sensor resistance changes with temperature, and the ECU compares this signal against expected ranges to detect shorts, opens, or out-of-range values indicating sensor malfunction or converter inefficiency.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Sensor Voltage | 0.5-4.5V (proportional to temperature) | <0.1V or >4.8V, no change over 10 seconds |
| Temperature Rise Rate | Steady increase after cold start | No change or erratic fluctuations |
Code P1425 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, P1425 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.