Downstream O2 Sensor (Rear, Post‑Cat) for Toyota exhaust systems

This rear oxygen sensor sits after the catalytic converter and tells the ECU if the catalyst is doing its job. It keeps fuel trims balanced, protects the converter, improves fuel economy, and helps your vehicle pass emissions tests. A healthy post‑cat sensor means stable cruising, clean exhaust, and no warning lights .

How it works

Inside is a zirconia ceramic cell that generates a small voltage based on oxygen content in the exhaust. A fast heater brings it up to temperature quickly. The ECU compares upstream vs. downstream signals: the rear sensor should show a steady, low‑activity waveform when the catalyst stores oxygen correctly.

If it fails ⚠️

Expect Check Engine Light, richer or leaner trims, poor MPG, failed inspection, and codes such as P0136/P0141 or catalyst efficiency codes (P0420/P0430). Misreads can lead to unnecessary converter replacement and increased emissions.

Tech notes

OEM‑grade element, stainless body, correct connector and lead length for plug‑and‑play. Install on a cold exhaust with an O2 socket, avoid twisting the harness, seal threads per spec, check for leaks, clear codes, and run a drive cycle ✅.

Compatibility

• 4Runner
• Fj Cruiser
• Hilux Surf
• Land Cruiser Prado