P0440
Catalyst Temperature Sensor High Input (Bank 2)
Powertrain Catalyst System Catalyst temperature monitoring 🟡 Moderate — Fix within a week
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What This Actually Means
In plain language — no jargon

The exhaust temperature sensor on Bank 2 is reading too hot, like a thermometer stuck on a high reading when the actual temperature is normal. The ECU thinks the catalytic converter is overheating when it probably isn't.

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Symptoms You May Notice
3 known symptoms for this code
Check Engine Light illuminated
Reduced engine performance or limp mode
Rotten egg smell from exhaust
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Embedded Systems Insight
What the ECU/ECM is actually computing

The catalyst temperature sensor (upstream of the converter on Bank 2) sends a voltage signal proportional to exhaust temperature. The ECM monitors this signal during warm-up and steady-state operation, comparing it against expected temperature curves. If the voltage exceeds the maximum threshold for too long, the fault is triggered.

Voltage & Parameter Thresholds

Parameter Normal Range Fault Condition
Sensor Voltage 0.2-4.8V proportional to 200-900°C >4.8V or sustained high reading
Temperature Rise Rate Gradual increase during acceleration Rapid spike or sustained >850°C
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Diagnostic & DIY Fix Guide
Check these in order — from cheapest to most complex
1
Engine air filter
Replace clogged filter to restore proper combustion and reduce excess heat generation.
2
Catalyst temperature sensor (Bank 2)
Disconnect and inspect connector for corrosion; clean with electrical contact cleaner or replace sensor if damaged.
3
Spark plugs and ignition coils
Replace worn plugs or faulty coils causing misfire, which overheats the catalyst.