P20EC–P20F0 SCR NOx Catalyst - Over Temperature Bank 1
The ECU has logged a fault on P20EC. The definition below is the exact wording the standard uses for this code.
Can you drive it? The engine light will stay on and the car may run in a reduced-power mode. Read the freeze-frame data to see the conditions the fault was logged under.
Which code is which
Same fault, different cylinder or bank — diagnosed the same way. Several set together usually means one shared cause.
| Code | Definition | Severity |
|---|---|---|
P20EC | SCR NOx Catalyst - Over Temperature Bank 1 | Investigate soon |
P20F0 | SCR NOx Catalyst - Over Temperature Bank 2 | Investigate soon |
The definition
P20EC: SCR NOx Catalyst - Over Temperature Bank 1.
P20EC is a manufacturer-specific powertrain code (the engine or gearbox). Its meaning is set by the carmaker rather than by the SAE standard, so a generic OBD-II reader will often show it as an unknown code or misread it.
What to check first
Cheapest and fastest checks first:
- Read the freeze-frame data stored with the fault - engine speed, load and temperature at the moment it logged tell you whether this happens cold, hot or under load.
- Check the connector at the part for corrosion, and that it is fully seated.
- Clear the code and see whether it returns, and under what conditions.
What actually causes this on a VAG
SCR is the AdBlue part of the exhaust - a catalyst that uses AdBlue to turn NOx into harmless nitrogen and water. This code means the exhaust temperature sensors reported that catalyst running hotter than it is designed to tolerate on bank 1. Almost every VAG car with AdBlue is a four-cylinder, so 'bank 1' simply means the exhaust. It matters because an SCR catalyst is permanently degraded by sustained overheating: the coating sinters and does not recover when it cools down. Almost always the heat is arriving from something happening further forward in the exhaust rather than from a fault in the SCR itself. Note that VW and Audi equipment may show the same event under its own wording - catalyst temperature too high, or exhaust gas temperature too high on bank 1 - and that is the same investigation, not a different fault.
Most likely causes, in order
- Exhaust gas temperature sensor reading high. These sensors drift with age, and a sensor reporting a temperature the exhaust never actually reached will trigger this code on a perfectly healthy catalyst. It is the cheapest thing to rule out: with the engine stone cold, compare all the exhaust temperature sensors in live data - they should all sit close to ambient and close to each other.
- A regeneration that ran too hot. Burning soot out of the particulate filter is deliberately hot, and on a VAG that heat comes from extra late injections inside the cylinder. An injector that dribbles or closes slowly, or a post-injection that runs long, puts more fuel into the exhaust than intended and the temperature runs away downstream. Look for stored injector or regeneration codes and read the freeze-frame data captured when this code set.
- A very heavily loaded particulate filter burning fiercely. Lots of short cold journeys and repeatedly interrupted regenerations leave a filter so full that when it finally does regenerate it burns far hotter than intended. Have the soot loading and the regeneration history read out rather than guessed at.
- Genuinely extreme running conditions. Sustained full load - towing up a long climb, or a hard motorway run while a regeneration happens to be running - can occasionally record a legitimate one-off. Worth considering if it set once, matches what you were doing at the time, and everything else checks out clean.
Worth knowing: Find out what made it hot before you clear it, and do not let anyone replace the SCR catalyst on the strength of this code alone. If it is setting repeatedly, or it set while you were driving normally, stop and investigate rather than carrying on - the same over-fuelling that cooks an SCR catalyst can melt a particulate filter in one journey. If the catalyst really has been cooked, expect NOx efficiency or AdBlue conversion codes to appear later; those are the consequence of this event, not a separate new fault.
Reading the code is the easy part
A code names the circuit that complained. What tells you why is watching the sensor behind it while the engine runs — and that is where a code reader stops and a diagnostic tool starts.
VAGPULSE reads every module in a VW, Audi, Skoda or SEAT — not just the engine — shows the live measuring blocks behind this fault, gives you the freeze-frame conditions it was logged under, and clears it once you have fixed it. It also does what a generic OBD reader cannot on a VAG: service resets, coding, adaptations, and Stage 1–3 flashing with your original file saved first.
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Common questions
What does P20EC mean?
P20EC means SCR NOx Catalyst - Over Temperature Bank 1. It is logged when the ECU sees this circuit outside its expected operating window.
Can I drive with P20EC?
The engine light will stay on and the car may run in a reduced-power mode. Read the freeze-frame data to see the conditions the fault was logged under.