P0420 Fix for Jeep Wrangler 4.0

The 4.0 inline-six will outlive us all — but its catalytic converter won't. P0420 (catalyst efficiency below threshold) is one of the most common codes on TJ and XJ Jeeps, whether from an aging cat, a header swap, or an exhaust rebuild after trail damage.

The Fix: 90° O2 Sensor Spacer

The Brockett Built 90° O2 sensor spacer threads into the downstream O2 bung and moves the sensor out of the direct exhaust stream, so the PCM stops setting the catalyst code. CNC-machined, M18x1.5 thread — the standard Jeep O2 size.

• The 4.0 is a single-bank engine — one spacer does it. $42, done.
• 10-minute install: thread the spacer into the bung, sensor into the spacer, clear the code.
• Downstream (after-cat) sensor only — never the upstream sensor.
• The 90° offset tucks the sensor up and out of the way — handy for off-road clearance.

Fits

Wrangler TJ 4.0 (1997–2006), Cherokee XJ 4.0, Grand Cherokee 4.0, and JK 3.8/3.6 (V6 — two banks, needs two). All M18x1.5.

FAQ

Will it work on my JK?
Yes, but the 3.8/3.6 V6 has two banks — if you have both P0420 and P0430, grab the 2-Pack.

Will it hurt anything?
No — the downstream sensor only monitors the cat; fuel trim is unaffected.

Legal note: designed for modified/off-road use — check local emissions laws.

Get the 90° O2 Sensor Spacer — $42 →

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