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What P0420 means for your Toyota Tundra
Your Tundra's ECM is reporting that the catalytic converter on Bank 1 is no longer cleaning exhaust gases effectively. On the 2007-2019 5.7L 3UR-FE V8, the well-documented secondary air injection (SAI) system failure is the most common root cause - when the SAI valves leak or the pump fails, raw fuel and unmetered air reach the cats and cook them. Toyota issued multiple TSBs (T-SB-0070-12, T-SB-0193-13) and a Customer Support Program ZE7 extending warranty on the SAI system for many 2007-2013 Tundras.
🎯 Top Causes on the Toyota Tundra
55%
#1 MOST LIKELY
Secondary Air Injection (SAI) System Failure
2007-2019 Tundras with the 5.7L 3UR-FE have moisture-prone SAI valves that stick open or leak, soaking the catalytic converters with raw fuel during cold-start enrichment. When the cats degrade, P0420 sets - usually alongside P2440, P2442, P2445, or P2447. Check Toyota Customer Support Program ZE7 warranty extension before paying out of pocket.
SAI Parts
$650-$1,400
Labor
$300-$600
Total
$950-$2,000
25%
#2 COMMON
Catalytic Converter Substrate Failure
The 5.7L V8 has four cats (two close-coupled, two under-body). The Bank 1 (passenger side on 3UR-FE) cat usually fails first because it sees the hottest exhaust. OEM Toyota replacement is $1,000+; CARB-compliant aftermarket Magnaflow/Walker runs $400-$700 per cat. Federal EPA cats are cheaper but illegal in CA, NY, ME, CO, WA.
Cat
$400-$1,100
Labor
$200-$350
Total
$600-$1,450
12%
#3 POSSIBLE
Downstream O2 Sensor (Bank 1 Sensor 2) Aging
Denso downstream sensors on the Tundra start reporting sluggish at 120k+ miles, falsely indicating a bad cat. Before condemning a $1,000 catalytic converter, scope the Bank 1 Sensor 2 voltage at 2,500 RPM cruise - it should hold steady around 0.6-0.7V. Rapid switching = bad cat; flatline = bad sensor.
Sensor
$80-$160
Labor
$60-$120
Total
$140-$280
🚗 Most Affected Tundra Model Years
| Year | Engine | Primary Cause | Typical Mileage | Notes |
|---|---|---|---|---|
| 2007-2009 | 5.7L 3UR-FE | SAI system failure | 70k-130k | Eligible for CSP ZE7 in many cases |
| 2010-2013 | 5.7L 3UR-FE | SAI valves + cat damage | 90k-160k | CSP ZE7 may apply through 10yr/150k |
| 2014-2019 | 5.7L 3UR-FE | Cat substrate failure | 110k-180k | SAI improved but not eliminated |
| 2007-2014 | 4.0L 1GR-FE V6 | O2 sensor or cat aging | 130k-200k | Much lower P0420 incidence than V8 |
🔧 How to Diagnose P0420 on a Toyota Tundra
- Scan for SAI codes FIRST. On a 5.7L Tundra, P0420 alone is rare - check for P2440, P2441, P2442, P2445, P2447. If any are present, the SAI system is your real problem, not the cat. Visit a Toyota dealer with your VIN to confirm CSP ZE7 (Customer Support Program) status before spending a dime.
- Inspect SAI valves at the intake manifold. On the 5.7L, the two SAI valves sit at the rear of each cylinder head. Pull the vacuum lines and check for moisture, rust, or stuck pintles. A leaking valve sends boost-air into the exhaust and confuses the O2 sensors. Dorman 911-201/911-202 valves run about $180 each.
- Live-scope the Bank 1 downstream O2. With engine warmed up and held at 2,500 RPM, the Bank 1 Sensor 2 voltage should sit around 0.65V with minimal swing. If it mirrors the upstream sensor (rapid 0.1V-0.9V switching), the Bank 1 cat is genuinely degraded. If it pegs at 0V or 1V, replace the sensor first.
Want a step-by-step walkthrough specific to your Toyota Tundra's year and mileage? Run a $5.99 AI diagnosis report - we narrow the cause to your year, engine, and symptoms.
❓ Toyota Tundra P0420 FAQ
Does Toyota cover P0420 on my Tundra under warranty?
Toyota Customer Support Program ZE7 extended the secondary air injection system warranty on many 2007-2013 Tundras (and Sequoias/Land Cruisers/LX570s) with the 5.7L 3UR-FE to 10 years or 150,000 miles. Bring your VIN to any Toyota dealer for a free check - if you qualify, repairs (often $1,500-$2,500 worth) are free.
Can I drive my Tundra with P0420?
Short-term yes, but expect fuel economy to drop 5-10% and you will fail OBD-II emissions inspections. If P0420 is paired with P2440/P2442 (SAI codes), driving longer worsens cat damage because raw fuel keeps hitting the catalytic converter.
How much does cat replacement cost on a Tundra 5.7L?
OEM Toyota cats run $1,000-$1,400 each. CARB-compliant Magnaflow direct-fit cats are $450-$700 per side. Labor is $200-$350 per cat. The Tundra has 4 cats total, but P0420 only affects Bank 1 (passenger side on 3UR-FE).
Is the Bank 1 cat the front or rear on a Tundra?
On the 5.7L 3UR-FE V8, Bank 1 is the passenger side (cylinders 1-3-5-7). The close-coupled cat is mounted directly to the exhaust manifold on that side. Do not confuse "Bank 1" with "front of vehicle" - that is a common misdiagnosis.
Will fuel-system cleaner fix P0420 on my Tundra?
No. Cataclean and similar products can sometimes mask a borderline cat reading for a few drive cycles, but they do not repair substrate damage or SAI failure. Save your $25 for a proper diagnosis.
See all P0420 causes (all vehicles) → · Related: P0420 + SAI codes on Tundra →