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'98 Voyager SWB 2.4

Got this code for 2nd time, each time after filling up at the same gas station.

Disconnected neg. battery cable 1st time. Lasted 3 months.

?--This gas station, can that happen? It is a service station, not a gas/minimart. The first time I felt a loss of power. But after filling up again elsewhere, got close to 24 mpg on long commutes (3 sp.).

Of course 3 months is a long time, but what a coincidence.

If I clear code again, will it still fail emissions?

So, what is the diagnostic procedure?

Has anyone heard of Maremont cat converters? Says they are a direct fit.
 

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It takes quite awhile to set a cat fault code as the PCM has to pass all the other monitors first and doesn't want any false calls as it would draw the attention of the EPA. Clearing the code also resets all the emission monitors and they have to start the tests all over again. It may not pass an emission test if the monitors haven't completed running. The cat is the last test to be run and it does so by watching the reaction of both upstream and downstream O2 sensors which have already passed their monitor.
Certain conditions must be met for the monitor to run:

Chrysler: The catalyst monitor will NOT run unless the Check Engine light is off, no fault codes are present, the fuel level is between 15 and 85 percent full, and the coolant temperature is above 70 degrees F. If these conditions have been met, the engine must have run at least 90 seconds, and the engine speed must be between 1,350 and 1,900 rpm. Idle vehicle for five minutes (to reach closed loop operation), the drive at a steady speed between 30 and 45 mph for two minutes.


There is a remote possibility that fuel quality may affect the monitor and the fault can be intermittent with a boarderline cat. A direct fit cat is the best way out as long as you don't reside in California. If the fault was erased and has returned, it is probably real.
 

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There are ways to eliminate this code but I would not endorse them unless your vehicle is exempt from emission testing and you just want to get rid of the SES light. The most common method is to move the downstream O2 sensor out of the flow stream by using an extender which is readily available in the Help section of you auto parts store. It is simply a spark plug anti-fouler and costs about $6-7. Those are easily spotted by your emissions testing agency by use of the inspection mirror when they inspect your exhaust system. The more discreet method is to put a 1.2K ohm resistor in series with the downstream O2 signal wire.

Both methods are commonly used when a US or Candian destination vehicle is moved to another Country that does not require emissions testing or for short term testing or track/racing only use.

It is reported that the P0420 code can show up when the catalyst efficiency drops as little as 5 to 10% from full efficiency.

IIRC most direct fit converters may still require some cutting, and clamping or welding because the OEM converters often come with a long section of exhaust pipe meant to interface directly with the muffler, and the downstream O2 sensor port is part of that assembly. That is not necessarily true on many imported cars.
 
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