P0420 on a Toyota Tacoma
P0420 means catalyst System Efficiency Below Threshold (Bank 1). On the Tacoma, a few causes come up far more than others.
What P0420 usually means on a Tacoma
P0420 on a Tacoma is a bank 1 catalyst-efficiency code that shows up as the original converter wears out on higher-mileage trucks. The downstream oxygen sensor stops seeing the exhaust cleaned up and the ECU flags the cat. On the four-cylinder 2TR-FE it's a single-bank system, while the V6s use a converter per bank. It's a slow, mileage-driven fault rather than a breakdown, and the light stays on steady with no real change in how the truck drives.
Most common causes on the Tacoma
- Aged original converter
High-mileage Tacomas simply wear out the factory cat, and efficiency declines with heat cycles and time.
- Slow downstream O2 sensor
A tired Denso rear sensor can imitate a bad cat; verify it before condemning the converter.
- Exhaust leak ahead of the cat
Tacomas see plenty of rust, and a leaking manifold or flex pipe skews the readings.
- Unresolved misfire or lean run
Raw fuel from a weak coil or lean condition overheats the cat; clear those codes first.
What P0420 costs to fix on a Tacoma
A four-cylinder Tacoma cat is a moderate part and reasonably accessible under the truck. The V6s cost more because they run two converters, and stolen-cat replacements on trucks add up quickly. Because Tacomas are theft targets for converters, always confirm the cat is actually inefficient — not just a lazy O2 sensor — before buying one.
Year, engine and mileage change the answer. Start a case and Redline weighs these causes against what your car shows, then names the check that would settle it.
Other codes on the Toyota Tacoma
Related symptoms
Toyota Tacoma problems & recalls by year
Based on widely reported patterns for this model; individual causes vary by year, engine and history. Generic P0420 behavior is covered on the main P0420 page. Confirm with a scan tool before buying parts.
P0420 on your Tacoma?
Every problem becomes a Case. Tell Redline what your Tacoma is doing: it shows what the evidence supports, what’s still missing, and what to check next, before you approve a repair.
“Inner pad ~1 mm. Outer pad 3 mm.”
Next: check the slide pins move freely before buying parts.