Hi folks, I'm a mechanic that is banging my head against a wall with two 2006 minivans. Both with 3.8L one a Grand Caravan and the other a Town and County. Replaced Catalytic Converter on both and replaced both (upstream and downstream) O2 sensors with NGK O2 sensors on both vans. I'm stumped with this one. Code comes back on both vans all the time. So much so that the Grand Caravan has the code set on the scanner but check engine light has become randomly on and off.


Anyone else out there seen this with the 06? or at all? I have no idea what to do on these and the dealer is being no help at all.

Thank you in advance,
ajcasper

 

a P0240 means Catalytic Converter is below threshold.

I have learned in my experience, there is nothing you can do when this code pops up EXCEPT to replace the CAT, I just went through the exact samething in my Honda, did you put a new cat on each or did you go to the jy and pick one up?

 

The PCM determines the cat is bad by the rate of cycle of the downstream O2 sensor. When the downstream O2 mirrors the upstream O2 it sets the code. How does the O2 sensors compare when the vehicle is warm?

 

cats are only about 2 months old. o2 sensor graphs look fine according to snap-on solus scanner

 

an exhaust leak before the cat can also cause that issue

 

I'll have to smoke the vans to see if there is a leak but no audible sound of a leak. and i normally here those right away when i drive the cars.

 

Try OEM CAT? I know they are expensive, but there really nothing else you can do.
or waranty another aftermarket Cat. it is 2 months old doesn't mean it can't be bad. I have a lot of experience with Aftermarket Cat going out in less than a yr.

 

Tizzy, our 05 GC popped a p420 this morning. It cleared and didn't come back while idling or revving the engine. I looked at 1/1 O2 V and 1/2 O2 V and 1/2 at idle was steady at 3.28, but 1/1 would bounce between 2.62ish (same as req. O2) and 3.28ish. Revving it would go higher. I'm new to all of this emissions and spark stuff because I'm a John Deere Tech for many years and we ain't got no sparks. Or O2 sensors.

So, since the 1/1 was bouncing, can I guess that the upstream O2 sensor is in the outhouse?

 

1/1 is the upsteam O2 sensor and it should fluctuate up and down. When the cat it warmed up and doing it's thing, the 1/2 sensor will kinda go to one side and be real lazy. That's what it should do. When the cat is bad, the 1/2 sensor will basically play follow the leader with the 1/1 sensor. Sometimes replacing just the downstream O2 sensor will cause the code because the old upsteam will have slowed down and with a fresh downsteam, the PCM gets faked out.

 

So until it becomes a problem, we can just let 'er buck and at that time it would be best to replace both. is that what I'm understanding.