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What P0420 means for your Sienna
Your catalytic converter is no longer cleaning exhaust gases effectively. On 2007-2016 Siennas with the 3.5L 2GR-FE V6, a known VVT-i oil supply line leak (rubber section) dumps oil onto the exhaust and into the cat. Toyota TSB T-SB-0017-08 addresses this. AWD models also see front-cat theft. The ECM detects this by comparing upstream and downstream oxygen sensor readings. You will fail emissions but the car is generally drivable short-term.
Top Causes on the Toyota Sienna 3.5L V6
50%
#1 CAUSE
VVT-i Oil Supply Line Leak Onto Exhaust
The 2GR-FE VVT-i oil line has a rubber middle section that cracks and leaks oil directly onto the exhaust manifold. Oil entering the exhaust burns and coats the catalyst with phosphorus and zinc deposits. Toyota TSB T-SB-0017-08 recalled the rubber line and replaced it with a fully metal unit. Many high-mileage Siennas have been retrofit but some still leak.
Parts
$80-$160
Labor
$200-$400
Total
$280-$560 (oil line only)
32%
#2 CAUSE
Catalyst Substrate Wear / Cat Theft
After oil contamination or natural aging past 150k miles, the cat substrate degrades. The Sienna has two cats (one per bank). AWD Siennas (2004-2010) are increasingly targeted for cat theft - check for cut sections under the car.
Parts
$700-$1,400
Labor
$300-$500
Total
$1,000-$1,900
18%
#3 CAUSE
Downstream O2 Sensor Failure
Each bank has its own pre and post-cat O2 sensor. Sluggish downstream sensors are common after 130k miles on the Sienna and trigger false P0420.
Parts
$60-$160
Labor
$60-$120
Total
$120-$280
Most Affected Sienna Model Years
| Year | Engine | Trim | Typical Mileage | Notes |
|---|---|---|---|---|
| 2007-2010 | 3.5L 2GR-FE V6 | CE, LE, XLE, Limited | 110k-170k | VVT-i oil line; TSB T-SB-0017-08 |
| 2011-2016 | 3.5L 2GR-FE V6 | L, LE, SE, XLE, Limited | 100k-160k | Updated line; still aging |
| 2007-2010 AWD | 3.5L 2GR-FE V6 | AWD LE, XLE | Any | Front cat theft target |
| 2017+ | 3.5L 2GR-FKS DI V6 | L, LE, SE, XLE, Limited | 70k-130k | DI carbon issues; new pattern emerging |
Is It Safe to Drive Your Sienna with P0420?
Short answer: If oil is leaking onto the exhaust, you have a fire risk - get the VVT-i line replaced quickly. P0420 alone is short-term drivable but will fail emissions.
How to Diagnose P0420 on a Toyota Sienna
- Inspect the VVT-i oil line. Look at the rubber section of the VVT-i oil supply line on the front of the engine. Any seepage, swelling, or smell of burning oil from the exhaust = leaking line. Toyota TSB T-SB-0017-08 specifies a fully metal replacement.
- Check for cat theft on AWD. AWD Siennas have an exposed front cat that thieves target. Look under the front of the vehicle. Loud exhaust on startup confirms theft.
- Verify downstream O2 with live data. Sluggish or flat-lined downstream O2 = sensor fault. Rapid switching matching the upstream = bad cat. The Sienna has two cats so isolate which bank set the code (P0420 = bank 1, P0430 = bank 2).
Want a full step-by-step diagnosis specific to your Sienna's year and mileage? Run a $5.99 AI diagnosis report with a printable summary you can show any mechanic.
Toyota Sienna P0420 FAQ
Is the Toyota Sienna VVT-i oil line covered under a recall?
Toyota TSB T-SB-0017-08 (technical service bulletin, not a recall) extends warranty coverage on the rubber VVT-i line for many 2007-2010 models. Bring your VIN to a Toyota dealer for current status.
How much to replace the Sienna catalytic converters?
Both cats with quality aftermarket parts and labor: $1,400 to $2,500. Toyota OEM cats run $2,200 to $3,500.
Why is my AWD Sienna a cat theft target?
The AWD Sienna has an exposed front catalytic converter that is easy to access from underneath. Thieves cut it out in 90 seconds. Install a cat shield with replacement.
Will fixing the VVT-i oil line fix the P0420?
Only if the cat is not already contaminated. If oil has been entering the exhaust for thousands of miles, the cat is likely permanently fouled and must be replaced along with the line fix.
See all P0420 causes and vehicles → · Related Sienna issue: VVT P0011 →