Checks, in order
- Read and write down all codesLook for sensor heater codes or misfire codes alongside the P0420. Fix those first since they can cause the catalyst code.easy $ · under about $50
- Exhaust leaks upstream of the sensorsListen and feel for leaks at the manifold, flex joints and gaskets with the engine cold. A leak lets air in and skews readings.easy $ · under about $50
- Oxygen sensorsCheck live data for lazy or stuck readings on the upstream and downstream sensors. Replace tired upstream sensors with the correct Toyota-spec part.medium $$ · about $50 to $500
- Misfires and fuel trimFix any misfire or rich/lean condition first. Unburned fuel damages the converter and sets the code again.medium $ · under about $50
- Catalytic converterIf everything above checks out and the downstream sensor mirrors the upstream, the converter is spent. Use a compliant replacement; some states require specific parts.medium $$$ · shop-level job, $500+
Applies to: 1995.5 to 2004 Tacoma with the 2RZ-FE 2.4L, 3RZ-FE 2.7L and 5VZ-FE 3.4L V6, 2WD, PreRunner and 4WD. Code-based checks assume OBD-II (1996 and newer); earlier trucks may use a different diagnostic setup.
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 1st Gen Tacoma problems
- Frame rust: flaking, holes or a soft frame (Frame & Body)
- Loose front end, steering wander or clunk from the lower ball joint (4WD/PreRunner) (Steering & Suspension)
- Clunk, knock or rattle going over bumps (Steering & Suspension)
- Steering feels loose or the truck wanders on the highway (Steering & Suspension)
- Vibration at highway speed or under acceleration (Drivetrain)
- 4WD won't engage or front axle doesn't seem to drive (Front Axle)
All 16 1st Gen Tacoma 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.