Catalyst Temperature Sensor Low Input (Bank 2)
The engine computer detected that the catalyst temperature sensor on the right side of the engine is reading too low, like a thermometer stuck in the cold zone. This usually means the sensor is broken, disconnected, or the wiring has a problem.
The ECU monitors voltage output from the catalyst temperature sensor on Bank 2 to verify the catalytic converter is operating at the correct temperature. The sensor sends a voltage signal proportional to temperature; if voltage stays below the minimum expected threshold, the ECU logs a low input fault.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Sensor voltage output | 0.5-4.5 volts (temperature dependent) | Below 0.1 volts or continuously below minimum threshold |
| Catalyst temperature range | 200-900°C during operation | Reading consistently below 200°C or sensor voltage stuck low |
Code P0438 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, P0438 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.