What P0420 means for your Q50
Your Q50's catalyst efficiency monitor has detected the converter is no longer cleaning exhaust effectively. The cause depends on your engine. On 2014-2015 VQ37VHR cars, the timing chain tensioner noise is a known precursor to combustion irregularities feeding the cat. On 2016+ VR30 twin-turbo cars, oil consumption from turbo seals leads the list.
🎯 Top Causes on the Infiniti Q50 (3.0L VR30DDTT / 3.7L VQ37VHR)
🚗 Most Affected Infiniti Q50 Model Years
| Year | Engine | Trim | Typical Mileage | Notes |
|---|---|---|---|---|
| 2014-2015 | VQ37VHR 3.7L V6 | Base, Premium, Sport | 90k-130k | Timing chain tensioner noise precedes cat issues |
| 2016-2017 | VR30DDTT 3.0T (300hp) | 3.0t Premium, Sport | 70k-110k | Twin-turbo seal wear; cat heat soak |
| 2016-2022 | VR30DDTT 3.0T (400hp) | Red Sport 400 | 60k-100k | Higher boost = higher exhaust temps, faster cat aging |
| 2014-2015 | 2.0L Turbo (Mercedes M274) | 2.0t | 80k-120k | Same M274 issues as Mercedes C300 |
⚠️ Is It Safe to Drive Your Infiniti Q50 with P0420?
If you own a Red Sport 400 and the cat is aging at 70k miles, do not just replace the cat. Document oil consumption first. If consumption exceeds 1 quart per 2,000 miles, Infiniti technical service may cover the turbos under powertrain warranty (6 yr/70k mi). After warranty, factor turbo seal repair into the budget.
🔧 How to Diagnose P0420 on a Infiniti Q50
- Check for active misfires. VR30 ignition coils have a recall (Infiniti Voluntary Service Campaign P9219) for misfire risk. Misfires destroy cats. Have all 6 coils inspected and replaced under campaign before any cat work.
- Run an oil consumption test. Fill to the full line, drive 1,000 miles under mixed conditions, recheck. If consumption exceeds 1 quart per 1,000 miles on a VR30, the turbo seals are likely the source. Address that before the cat or expect the new cat to fail within 30k miles.
- Pull O2 sensor live data with CONSULT-III or capable scanner. Watch B1S2 (Bank 1 downstream) at 2,500 RPM warm. Healthy: steady at 0.6-0.7V. Failed cat: switching like B1S1. Failed sensor: stuck at one voltage.
❓ P0420 Infiniti Q50 FAQs
Is P0420 covered under Infiniti warranty?
Federal emissions warranty covers the cat for 8 years/80,000 miles. Infiniti powertrain warranty is 6 years/70,000 miles. CPO Infiniti adds another 1 year/15,000 miles. Check VIN-specific coverage at infinitiusa.com.
How much to fix P0420 on a Q50?
Cat replacement alone: $1,000-$2,000. If turbo seals also need attention (VR30 models): add $2,200-$4,300. Most cases are cat-only at $1,200-$1,800.
Does the Q50 Red Sport eat cats faster?
Yes. The 400hp tune produces higher exhaust temperatures than the 300hp 3.0t. Red Sport owners commonly see P0420 around 60k-100k miles compared to 90k-130k on the standard 3.0t.
Can I use an aftermarket cat on my Q50?
Yes for federal emissions states. California, New York, Colorado, and Maine require CARB-EO compliant direct-fit cats - typically Magnaflow, Walker, or Eastern with EO number printed on the cat.
Will an aftermarket downpipe solve P0420?
Catless or high-flow downpipes are not street legal in any US state and will set P0420 immediately. They are track-use only.