P0428
Catalyst Temperature Sensor Low Input (Bank 1)
Powertrain Catalyst System Catalyst Temperature Sensor 🟡 Moderate — Fix within a week
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What This Actually Means
In plain language — no jargon

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.

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Symptoms You May Notice
3 known symptoms for this code
Check Engine Light illuminated
Possible rough idle or slight hesitation during acceleration
Reduced fuel economy
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Embedded Systems Insight
What the ECU/ECM is actually computing

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.

Voltage & Parameter Thresholds

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
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Diagnostic & DIY Fix Guide
Check these in order — from cheapest to most complex
1
Electrical connector and wiring harness
Inspect the CTS connector and wiring for corrosion, loose terminals, or damaged insulation and clean or reseat as needed.
2
Catalyst temperature sensor
Replace the faulty sensor with an OEM or quality aftermarket part, ensuring proper installation in the exhaust manifold.
3
Catalytic converter
If the converter is severely degraded or clogged, it may not reach proper operating temperature and should be replaced.