OBD Code P0440: Catalyst Temperature Sensor High Input (Bank 2)

Q: What does OBD code P0440 mean?

Catalyst Temperature Sensor High Input (Bank 2). 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.

Q: What are the symptoms of fault code P0440?

Check Engine Light illuminated, Reduced engine performance or limp mode, Rotten egg smell from exhaust

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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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How Your ECU Detects This

Technical sensor logic and voltage thresholds

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.

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When to See a Professional Mechanic

Not all fault codes are safe to DIY

Code P0440 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.

Safety note: OBD-II codes identify the system or circuit where a fault was detected — they do not always identify the exact failed component. A professional mechanic using live sensor data will diagnose the root cause more accurately than replacing parts based on the code alone.

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How to Clear Code P0440

What happens after you fix the fault

Once the fault is repaired, P0440 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.

✅ Safe to Clear When

Fault has been diagnosed and repaired
You want to confirm the repair worked
Code appeared after a sensor was cleaned

⚠️ Do Not Clear When

Preparing for an emissions/PUC test
Root cause is still undiagnosed
Check engine light is flashing

Emissions test note: Clearing codes resets OBD readiness monitors. Most vehicles need 50–100 km of mixed driving before monitors complete. Do not clear codes immediately before an emissions or PUC inspection.