P0424 means the temperature of the heated catalyst on Bank 1 (an electrically heated e-cat used on newer Euro 6 and 6d vehicles) is not rising fast enough or not reaching the expected level during cold start. Unlike P0423 which is an efficiency code, P0424 is specifically about the heater not delivering enough thermal energy.
DTC/P0424·Audi
P0424 on Audi: Causes, Symptoms and Fix Cost
Quick Answer
Moderate SeveritySafe to drive (short-term)Audi
P0424 on a Audi means the temperature of the heated catalyst on Bank 1 (an electrically heated e-cat used on newer Euro 6 and 6d vehicles) is not rising fast enough or not reaching the expected level during cold start. Unlike P0423 which is an efficiency code, P0424 is specifically about the heater not delivering enough thermal energy.
Repair cost on Audi€156 - €3016
What does P0424 mean on a Audi?
Audi A6
2019-2024The C8 A6 3.0 TFSI (EA839) V6 mild-hybrid sets P0424 most often after winter storage when the 48V battery has self-discharged. The heater requires full 48V supply within milliseconds of start, and even slight voltage sag prevents the catalyst from hitting its temperature target. Always test the 48V battery state of health and DC-DC converter ripple before replacing the e-cat assembly.
What causes P0424 on a Audi?
Beyond the generic causes listed on the main P0424 page, these are the Audi-specific patterns we see most often:
Audi A6Winter self-discharge of 48V battery preventing heater activation
Audi A6DC-DC converter ripple at cold temperatures cutting heater current
How to diagnose P0424 on a Audi with OBD2
Follow these steps to pinpoint the root cause of P0424:
- Read freeze frame and confirm the code set during the first 60 to 90 seconds of cold start, which is the typical fault window for P0424
- Check for any heater-circuit-specific codes (manufacturer-specific) and inspect the relevant fuse, often shared with the e-cat heater relay
- Measure heater element resistance per OEM spec (typically 0.3 to 2.0 ohms). Open circuit means the element has failed
- Inspect the wiring harness from the heater relay to the catalyst connector for chafing, water ingress, or melted insulation near the exhaust
- Use a clamp meter to verify current draw at start (commonly 30 to 80 A briefly). Insufficient current points to a relay, wiring, or 48V supply fault
How much does P0424 cost to fix on a Audi? (EUR)
Estimated repair costs on a Audi (Audi parts and labour typically run 30% above the average for this code).
Prices estimated as of May 2026. Costs vary by region, vehicle, and shop.
Related codes that often appear with P0424 on Audi
These codes commonly cluster with P0424 on Audi vehicles:
FAQ: P0424 on Audi
What is the difference between P0423 and P0424?
P0423 is an efficiency code (the heated catalyst is not converting emissions well enough), while P0424 is a temperature code (the heater itself is not getting the catalyst hot enough fast enough). P0424 most often points to a wiring, relay, or heater element fault rather than the catalyst substrate.
Can a fuse cause P0424?
Yes. The e-cat heater is driven through a high-current fuse, typically 40 to 80 A. If that fuse blows, the heater never activates and P0424 will set within the first cold start after the blown fuse. Always check the e-cat heater fuse before assuming the catalyst itself has failed.
How can I test if the heater element itself is dead?
With the connector unplugged from the catalyst, measure resistance across the heater terminals with a multimeter. Compare against the manufacturer specification, which is typically between 0.3 and 2.0 ohms. An open circuit or a resistance well outside spec means the heater element has failed and the catalyst assembly needs replacement.
Will P0424 trigger limp mode?
Usually no. Most manufacturers treat P0424 as a non-driveability emissions fault and only illuminate the check engine light. The car will run normally but cold-start emissions will be elevated. Limp mode only triggers if other serious faults are present alongside the heater fault.
Looking for the full P0424 reference (all makes, full diagnosis flow, complete repair cost matrix)?
See the main P0424 guideSkanyx · Audi
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