It came back. Just once so far. I guess I need to let the boss know to expect a couple of O2 sensors this Spring?

 

Most of the time when it sets the cat failure code, you need a cat. I replace both O2 sensors when I do one. You can try replacing both O2 sensors first. Obviously it's not totally wiped out since it takes so long to set it.

 

Earlier there was mention of an exhaust leak upstream causing this, but would that be a consistent code?

 

depends on the leak, but I would assume more frequent than you are getting.

 

EPA emissions is a bunch of crap if you ask most people. i spend more time chassing EVAP and O2 sensor issues than probably anything else.

Still having the same issues with those caravans. The code will stay clear long enough to make it through emissions testing but comes back after only a short time.

Does anyone know why I only seem to have this particular reoccurence with 06 grand caravans with sto-n-go. Just a bad build year for the 3.8?

If any one has the diagnostic tree for this model it would be appreciated.

 

Symptom:
P0420-CATALYTIC 1/1 EFFICIENCY

When Monitored and Set Condition:
P0420-CATALYTIC 1/1 EFFICIENCY

When Monitored: Engine Run time greater than 90 seconds. Engine Coolant greater than
70°C (158°F) Vehicle speed greater than 20 MPH and less than 55 MPH. Engine Speed
greater than 1216 RPM and less than 1952 RPM.
Set Condition: As catalyst efficiency deteriorates, the switch rate of the downstream O2
sensor approaches that of the upstream O2 sensor. If at any point during the test the
switch ratio reaches a predetermined value a counter is incremented by one. One Trip
Fault.

POSSIBLE CAUSES

GOOD TRIP EQUAL TO ZERO
VISUALLY INSPECT CATALYTIC CONVERTER
EXHAUST LEAK
ENGINE MECHANICAL CONDITION
AGING O2 SENSOR
CATALYTIC CONVERTER

TEST ACTION APPLICABILITY

1

Ignition on, engine not running.
With the DRBIII

144

DRIVEABILITY - NGC

Inspect the Catalytic Converter for the following damage.
Damaged Catalytic Converter, dent and holes.
Severe discoloration caused by overheating the Catalytic Converter.
Catalytic Converter broke internally.
Leaking Catalytic Converter.
Were any problems found?
All
Yes

! Replace the Catalytic Converter. Repair the condition that may
have caused the failure.
Perform POWERTRAIN VERIFICATION TEST VER - 5.
No ! Go To 3
3 Start the engine.
Inspect the exhaust for leaks between the engine and the O2 Sensor.
Inspect the exhaust for leaks between the engine and the appropriate rear O2 Sensor.
Are there any exhaust leaks?
All
Yes ! Repair or replace the leaking exhaust parts as necessary.
Perform POWERTRAIN VERIFICATION TEST VER - 5.
No ! Go To 4
4 Check the exhaust for excessive smoke caused by an internal problem in the engine.
Is a engine mechanical condition present?
All
Yes ! Repair the engine mechanical condition as necessary.
Perform POWERTRAIN VERIFICATION TEST VER - 5.
No ! Go To 5
5 A new rear O2 Sensor along with an aging front O2 Sensor may cause the DTC to set.
Review the vehicles repair history.
Has the rear O2 Sensor been replaced without replacing the front O2 Sensor?
All
Yes ! Replace the Front O2 Sensor as necessary.
Perform POWERTRAIN VERIFICATION TEST VER - 5.
No ! Go To 6
6 If there are no possible causes remaining, view repair. All
Repair
Replace the Catalytic Converter.
Perform POWERTRAIN VERIFICATION TEST VER - 5.

145

DRIVEABILITY - NGC

P0420-CATALYTIC 1/1 EFFICIENCY — Continued

 

Thanks, Tiz.

I see that silicone could cause this but what about antiseize on the spark plug threads?

 

SO I have been doing some learning about O2 sensors and such. Tizzy, you probably said this before, but sometimes, it takes a different view for me to understand things.

Feel free to correct me where needed:

The precat O2 sensor (O2S1) is the closed loop of the fuel/air ratio. It reads a rich condition and tells the ECU so the ECU leans out the mixture. The O2S1 sees the lean condition and reports back to the ECU. So when watching the output of the O2S1, it will go up and down, up and down. This voltage reading will go from about .2 volts to .8 volts.

The cat is in there evening out the rich/lean conditions with the downstream O2 Sensor (O2S2) making sure that the cat is doing it's job.

So, once the cat warms up, the O2S2 should be reading a nice, steady number while the O2S1 bounces between .2-ish and .8-ish.

When I looked at the O2S1 on our Subaru (that was throwing a P0032 code) and saw that it was flatlined at 2.158, this means that the O2S1 is bad.

I think I'm missing something about how things work cold Vs, warm, but I think as far as the Sub is going, the O2S1 is bad, but I still need to watch the Dodge Van to see what exactly it is doing. Now that I have done more reading and explaining, maybe I'll be able to understand what I'm looking for better.

 

parts of your thinking is right. But not all.
Subaru and few other newer Imports like Honda and Toyota uses Air/Fuel sensor. Those sensor states flat line, it doesnt bounce around. Rich condition, it stays on Higher voltage, lean condition, it goes low voltage.

Also, Dodge/Jeep/Chrysler is the only manufacturer that runs a 5volt reference toward the signal wire of the O2 sensor, the purpose is to detect a circuit failure on the sensor. When you look at the scanner, on the same sensor, there are 2 PID, on is from 0.2-0.8v, another one is like subtract the signal from a 2.5volt reference or something like that....
you have to compare apple to apple.

for CAT effieciency code's concern, the Computer is programed to look for "Different reading" between sensor 1 and Sensor 2. If they read completely different, the CAT works fine. If they read exactly or almost the same, it will give u a Cat efficiency code. that's for chrysler...
if you getting into other make and model, they all have different set up. you look at a Super car like Corvett, it has an A/F sensor after every single cylinder. some Corvett has 8 upstream sensor, and 2 down stream sensor. It could get extremely confusing if you try to figure out exactly how it work.

 

Found the issue as to why these codes keep getting thrown after replacing the CAT and O2 sensors.

It is aftermarket O2 sensors. Put the ones from the factory in the vans and they have not been back since.

Seems that all aftermarket ones dont read the same as the factory ones. They can be same part number as the factory ones but now physically look the same or behave the same in car when looking at a graphical printout of the data being sent back to the computer.