P0420 / P0430 Fix for Chevy Silverado & GMC Sierra 5.3 V8

Check engine light on your 5.3 Vortec or EcoTec3 with a P0420 or P0430 (catalyst efficiency below threshold)? On GM V8s this usually shows up after headers, high-flow cats, an aging factory cat — or just high miles. The truck runs fine, but the light won't stay off.

The Fix: 90° O2 Sensor Spacer

The Brockett Built 90° O2 sensor spacer threads into your secondary (downstream) O2 bung and moves the sensor out of the direct exhaust stream, so the ECM stops flagging catalyst-efficiency codes. CNC-machined with the standard M18x1.5 thread — a direct fit for GM downstream sensors.

• Your 5.3 has two banks — you need two spacers. P0420 is bank 1, P0430 is bank 2. Grab the 2-Pack V8 Kit and save.
• 10-minute install per side: thread the spacer into the bung, thread the sensor into the spacer, clear codes.
• Downstream (rear) sensors only — never install on the front/upstream sensors.

Fits These Trucks

Silverado 1500 & Sierra 1500 with 4.8L, 5.3L, 6.0L, and 6.2L V8s (1999–present), plus Tahoe, Suburban, Yukon, and Avalanche with the same engines. All use M18x1.5 O2 threads.

FAQ

Will this fix my P0420 for good?
If the code comes from low catalyst efficiency (common after exhaust mods or on aging cats), yes. It won't fix a bad O2 sensor or an exhaust leak — fix those first.

One spacer or two?
Two. Every GM V8 has a downstream sensor per bank. If you only have P0420 today, P0430 usually follows.

Is it legal?
Designed for modified/off-road use — check your local emissions laws before installing.

Get the 90° O2 Sensor Spacer — $42 single / $84 V8 2-Pack →

TIG-welded and machined by Brockett Built in central Illinois. Ships same or next business day. 30-day fitment guarantee.