Checks, in order
- Look for other codes firstMisfire or lean codes stored with P0420 mean you must fix those first, or the new converter will fail too.easy $ · under about $50
- Exhaust leaks upstream of the sensorsListen at cold start for ticking and inspect the manifold flanges and flex joints for soot streaks. A leak ahead of a sensor can skew its reading.medium $ · under about $50
- Oxygen sensor responseOn a scan tool, watch the rear sensor voltage. A healthy converter gives a mostly steady rear signal, while a rear sensor that mirrors the front one points to a worn converter or a lazy sensor.medium $ · under about $50
- Replace the sensor if it is agedOriginal sensors on high mileage trucks are a reasonable first replacement, since they are cheaper than a converter and often resolve the code.medium $$ · about $50 to $500
- Catalytic converterIf the sensor and exhaust are good and the code returns, replace the converter. Use a quality unit that meets your state's emission rules.hard $$$ · shop-level job, $500+
Applies to: 5th generation 4Runner, 2010 to 2024, with the 1GR-FE 4.0L V6 and the 5-speed automatic. Assumes the stock configuration; trim-specific items (KDSS, sunroof, A/C) are noted where they apply.
Tools and parts for these checks
Links below are Amazon affiliate links: as an Amazon Associate, toyotadata earns from qualifying purchases, at no extra cost to you. Confirm fitment for your exact truck before you order.
| ITEM | USED FOR | BUY |
|---|---|---|
| Bluetooth OBD2 scanner with live data | Reading and clearing codes and watching live sensor data | Shop on Amazon |
| Downstream oxygen sensor | Replacing a lazy rear O2 sensor before condemning the converter | Shop on Amazon |
More 5th Gen 4Runner problems
- Rust on the frame, flaking, or holes in the frame rails (Frame & Body)
- KDSS warning, fluid leak, or clunking and uneven ride on a KDSS truck (Steering & Suspension)
- Oil leak or oil smell from the front of the engine (Engine)
- Rough idle, shaking, or misfire with a flashing check engine light (Fuel & Ignition)
- Check engine light with P0171 or P0174, system too lean (Fuel & Ignition)
- Temperature gauge climbing, coolant loss, or overheating (Cooling)
All 16 5th Gen 4Runner symptoms in the interactive troubleshooter →
General guidance from owner experience. Confirm torque specs, fluid capacities and procedures in the factory service manual. Brakes, steering and anything structural: if in doubt, have a qualified shop inspect it before driving.