Catalyst Temperature Sensor Low Input (Bank 1)
The exhaust catalyst temperature sensor on Bank 1 is sending a signal that's too low, like a thermometer stuck reading ice-cold when it's actually hot. The engine computer expects this sensor to report higher temperatures to verify the catalytic converter is working properly.
The catalyst temperature sensor (CTS) monitors exhaust heat downstream of the catalytic converter to verify converter efficiency. The ECM expects the sensor voltage to stay above a minimum threshold during normal operation. If the voltage signal remains abnormally low for a set duration, the fault is triggered.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Sensor Voltage | 0.5–4.5 volts (depending on temperature) | Below 0.2 volts or stuck low |
| Catalyst Temperature | 200–800°C during operation | Reading consistently below 200°C when running |
Code P0428 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, P0428 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.