Understanding P0420 on Your 2024 Audi Q5
A P0420 code on your 2024 Audi Q5 indicates the ECM has detected reduced catalytic converter efficiency. The 2024 Q5 continues with the 2.0L TFSI turbocharged four-cylinder producing 261 horsepower with standard quattro AWD, while the SQ5 uses a 3.0L TFSI turbo V6 with 349 horsepower. On a vehicle this new, warranty coverage makes this a straightforward dealer visit.
Symptoms
- Check engine light and dashboard warning — Primary indicators
- Normal driving experience — Performance unchanged
- Slight MPG change — Minimal impact
- Possible exhaust smell — Faint sulfur odor
- Emissions failure — In testing states
Probable Causes
1. Software Calibration
ECM software refinements are common across the Audi lineup. The 2024 Q5's catalyst monitoring algorithms may need updated thresholds. A dealer software update is the simplest and most common fix for P0420 on new vehicles.
2. O2 Sensor Defect
A factory-defective downstream O2 sensor can cause false readings. The turbo engine's extreme exhaust heat can expose sensor flaws early in the vehicle's life.
3. Converter Manufacturing Issue
A catalytic converter that left the factory with insufficient catalyst coating or internal damage will underperform. This is fully covered under warranty.
4. Exhaust Connection Problem
An improperly sealed gasket or loose connection from the factory creates a leak that affects sensor accuracy. Check turbo outlet, downpipe, and converter connections.
Next Steps
- Schedule an Audi dealer visit — All repairs covered under warranty.
- Ask about TSBs and software updates — Common first-step fix.
- Drive normally — No restrictions needed.
- Keep records — Document for service history.
Cost (If Out of Warranty)
- Software update: $0 under warranty ($150 – $250 otherwise)
- O2 sensor: $0 under warranty ($180 – $420 otherwise)
- Catalytic converter: $0 under warranty ($1,600 – $3,300 otherwise)
- Exhaust repair: $0 under warranty ($150 – $500 otherwise)
Safe to Drive?
Yes, completely. Your 2024 Q5 is safe with P0420. The quattro system, pre-sense safety features, and all driving systems work normally. Schedule a dealer appointment at your convenience.
Prevention
- Use premium fuel — Required for the TFSI engines
- Follow Audi's service schedule — Regular maintenance prevents issues
- Address all codes promptly — Don't let small problems become big ones
- Use Audi-specified oil — Correct oil grade prevents engine deposits