P0420 and P0306

[Cfbrenton1]

Hey everyone,

My warning lights came on and my 2007 LX470 is showing codes P0306 and P0420. The Toyota dealer, which isn't accustomed to seeing many of these vehicles quickly jumped to "it needs $2100 cats". Do you think this is the case? Or should I try other things? Note - I was recently on a trip where I was forced to put one tank of 87 octane in. The lights didn't come on when I was using that gas, but they did two days later.

Any thoughts or suggestions would be great.

Thanks!

 

[tacoduck]

Dreaded Catalytic converter fault codes

I like the idea of doing the spark plugs and making sure the thermostat is running right. My 07 with lots of dealer service had 140k miles on the spark plugs. plugs looked bad!

 

[DirtDawg]

P0306 is cylinder 6 misfire, so I would solve that issue (prob coil packs), and see if the cat code is still there. Is it misfiring?

 

[LandCruiserPhil]

Hey everyone,

My warning lights came on and my 2007 LX470 is showing codes P0306 and P0420. The Toyota dealer, which isn't accustomed to seeing many of these vehicles quickly jumped to "it needs $2100 cats". Do you think this is the case? Or should I try other things? Note - I was recently on a trip where I was forced to put one tank of 87 octane in. The lights didn't come on when I was using that gas, but they did two days later.

Any thoughts or suggestions would be great.

Thanks!

Dont see gas as the problem only because I have owned several 100 series and RARELY use anything other than 87 octane.

 

[tacoduck]

new plugs and check the coils as well.

 

[cwininger]

p0420 could be bad gas cap or o2 sensors. i would do both of those before even considering new cats. and your dealer is a moron.

 

[landylover21]

When I had the 0420 code I swapped out my downstream O2 sensors and bang, it's been gone for three years now. I also ended up putting in new upstreams for the hell of it a couple months later.

 

[99toylc]

Replace O2 sensors with Denso replacements - for some reason these trucks are super sensitive when you put German parts in them (Bosch) or other.

 

[aging fleet]

Note - I was recently on a trip where I was forced to put one tank of 87 octane in.

I wouldn't worry about 1 tank of 87, I don't think mine has ever been filled with premium.

Side note, I was in Chagrin Falls with the family over the weekend visiting friends, that's a really nice community.

 

[2001LC]

Hey everyone,

My warning lights came on and my 2007 LX470 is showing codes P0306 and P0420. The Toyota dealer, which isn't accustomed to seeing many of these vehicles quickly jumped to "it needs $2100 cats". Do you think this is the case? Or should I try other things? Note - I was recently on a trip where I was forced to put one tank of 87 octane in. The lights didn't come on when I was using that gas, but they did two days later.

Any thoughts or suggestions would be great.

Thanks!

CATs rarely fail.

A bit more info would be helpfully:
How many miles on spark plugs, and are they factory?
How does air filter look, how many miles on it?
When (miles ago) was MAF & throttle body cleaned and was battery disconnected for 30 minutes at that time?

P0306 is cylinder 6 misfire, so I would solve that issue (prob coil packs), and see if the cat code is still there. Is it misfiring?

IIRC you nailed the code.

Swapping number 6 coil (PS 3rd one back, from front) with any other one to see if code moves is SOP.

 

[Cfbrenton1]

Thanks for your help everyone. I don't know if the spark plugs have ever been replaced? I don't know if it has been misfiring since my wife usually drives it. The truck has about 110k miles. One update is that the lights were turned off, stayed off for a few days, turned back on for a few hours and now turned themselves off. Seems like if the cats were bad, it wouldn't turn off?

 

[cwininger]

Sounds like o2 sensor(s). Swap out both downsptream ones (10 minute job). A worn out gas cap can cause codes like these too.
https://amzn.com/B000C5SG8G

 

[Dwight S]

Go to AutoZone and let them check the codes since they were cleared at the dealer. The P0306 should be a coil pack, easy to replace, been there, done that. The P0420 sensor fault should also be fairly easy to replace as well.

 

[tacoduck]

The spacer fixed my check engine light, but Im bothered by my exhaust being extra stinky. Im wondering if my upstream sensor is bad, which is causing my truck to run rich. Mechanic said it was working fine, but I'm still trying to figure out this stinky exhaust!

 

[Cfbrenton1]

Update.... The lights turned themselves off and have not come on again. I have driven a couple thousand miles... Is it a ghost? Bad gas?

I keep waiting to see those lights turn on again, but they don't. I know the second I press enter on this thread, they will turn on! haha