2006 Toyota Highlander 3.3 V6 Check Engine Light and Oil Issue
I have a 2006 Toyota Highlander (3.3 v6) with 243k miles on it. Bought it a few months ago. Previous owner had changed catalytic converter for Bank 2 before selling it. So the issues were like this. I made like 4k miles on it. Check engine light appeared. I then noticed it was quite low on oil. Had to put over half a gallon to top it off. After few miles light went off. It now appeared again and it’s not going. Oil is still full. I checked with a scanner and those two codes appear. My question is, could both codes be related? I read that P0021 can come when low on oil / dirty oil because of the vvt valve. So hopefully not a big deal. Could that also trigger the P0420 or that is unrelated and it is because the catalytic converter is dead? So what I think of doing is changing the oil (it is time) and the vvt valve (easy fix) and clearing the codes. So my hope is that will fix P0021 and I want to know if it is possible for that change to make P0420 not appear again at least for a while.
You’ve got two codes: P0021 (VVT performance Bank 2) and P0420 (Catalyst efficiency Bank 2). The VVT code can absolutely be triggered by low or dirty oil, and sometimes a sticky VVT solenoid. The catalyst code is usually about the cat itself or the downstream O2 sensor, but a VVT issue can cause poor combustion and temporarily mess with catalyst readings.
Most likely culprits
- Dirty or old engine oil — VVT system needs clean oil; dirty oil can stick the solenoid and trigger P0021.
- Sticky Bank 2 VVT solenoid — If oil change doesn’t clear P0021, solenoid is a common failure.
- Catalytic converter efficiency issue — If P0420 persists after VVT is fixed, cat or downstream O2 sensor is suspect.
How to narrow it down
- Change the oil and filter — Use the correct viscosity. Clear codes. If P0021 stays gone, oil was the root cause.
- Drive 50-100 miles — Let monitors reset. If P0420 returns, VVT wasn’t the only issue.
- If P0021 returns after oil change — Swap Bank 2 VVT solenoid (easy, cheap). Clear codes and retest.
- If P0420 returns after VVT is fixed — Check downstream O2 sensor readings with scanner. If switching like the upstream, cat is likely bad.
- Check for exhaust leaks near Bank 2 — Small leaks can trigger P0420.
- If both codes return after all above — You’re looking at a deeper engine issue (burning oil, worn rings) or a bad replacement cat.
Possible parts (if needed)
- Bank 2 VVT solenoid (only if oil change doesn’t clear P0021)
- Bank 2 catalytic converter (only if P0420 returns after VVT issue is resolved)
- Downstream O2 sensor (only if sensor is lazy or stuck, confirmed by scan data)
A few questions
- How long did the oil stay low before you topped it off? (Long-term low oil can damage VVT and cat.)
- Was the replacement cat OEM or aftermarket? (Aftermarket cats often trigger P0420.)
- Any signs of oil consumption or blue smoke from the exhaust lately?
Change the oil first, clear the codes, and see what comes back. Don’t throw parts at it until you know which code is persistent after the oil and VVT are sorted.