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Need Troubleshooting Help

Old 09-24-2007, 09:35 AM
Thread Starter
Join Date: Sep 2007
Posts: 4
Default Need Troubleshooting Help

With DTC P0421 is there any chance I don't need a Cat?

140,000K miles.On occasion hesitation/miss on acceleration at low RPM (about 2000 RPM).

Trouble code indicates Right Rear O2 sensor and/orcatalytic converter. All are original.

Here is the data from the reader that lit the MIL:

DTC for which Freeze Frame was StoredP0421
Fuel System 1 StatusClosed Loop
Fuel System 2 StatusClosed Loop
Calculated LOAD Value38.82 %
Engine Coolant Temp195.80 °F
Short Term Fuel Trim - Bank 1-4.69 %
Long Term Fuel Trim - Bank 13.91 %
Short Term Fuel Trim - Bank 22.34 %
Long Term Fuel Trim - Bank 23.91 %
Engine RPM1866 rpm
Vehicle Speed Sensor38.53 mph
Old 09-24-2007, 02:36 PM
Senior Member
Join Date: Aug 2007
Posts: 1,324
Default RE: Need Troubleshooting Help

A p0421 always means converter. There is an o2 in front and behind the converter. The o2 behind the converter only monitors cat efficiency. The one in front is the input to the PCM to switch lean/rich mixture. The PCM compares the front and rear o2 sensors and if they read the same or close it means the cat is not cleaning up unburned fuel. Of course if you have 2 old o2 sensors and put 1 new one in they may read far enough apart to not kick the code but not likely.
Old 09-24-2007, 03:56 PM
Thread Starter
Join Date: Sep 2007
Posts: 4
Default RE: Need Troubleshooting Help

Thanx, hixx.

I noticed that most of the posts regarding a bad cat indicate don't describe a hesitation as part of the problem when the CAT is bad. Since I have a hesitation, is it because the CAT is clogged or is there an outside chance that something else (bad plug or wire) could be causing this DTC? Or would I have gotten additional DTCs if that was the case?
Old 09-26-2007, 06:51 PM
Senior Member
Join Date: Aug 2007
Posts: 1,324
Default RE: Need Troubleshooting Help

If you have hesitation and a cat code it would be a safe bet the converter is partially clogged. You will still need to check the tune though as something caused the converter to quit working. Only an inefficient converter can cause a p0421 code other than a PCM malfunction which is unheard of as far as i have seen. Something caused it so the P0421 code is a result of tune usually. So your not done if you simply replace the converter.
Old 12-09-2007, 09:50 PM
Join Date: Nov 2007
Posts: 6
Default RE: Need Troubleshooting Help

I have a 2001 MPV. I already replaced my MAF sensor and my IMRC. Those were the codes that it spit out. I also found a vacuum leak in the pcv hose and got that replaced. I went to Auto Zone and got the codes read again. There are no codes being displayed anymore. Nice repair job right??!! Wrong!! I still have major hesitation. It almost stalls when I sit at a light and when I hit the pedal to go, it is REALLY sluggish(kinda like bad gas). When I FINALLY hit the speed limit, it evens out somewhat. But when I try to accelerate, it does not want to go like it used to. The plugs have been replaced(with Champion plugs) and the problem still isn't fixed. Should I have used a higher end plug?? Might I have a clogged fuel filter or injector?? It also backfires a little when I do try to accelerate. Can anyone point me in the right direction before I fall into the DEALERSHIP TRAP?? I am a do-it-yerselfer so I would rather fix it myself. But with no codes, I don't know where to begin. HELP!!!
Old 12-28-2007, 08:42 AM
Join Date: May 2007
Posts: 2
Default RE: Need Troubleshooting Help

Jim, Please let me know what you find w/your problem.
I am having similar w/my '97 mpv.
Plug wires + dist + coil etc. are my next checks.
FWIW it is due back at the dealer for re-diagnosis as their first diag of "corroded fuel tank/clogged fuel pump" ($100 to tell me it needs $1K repairs) proved ~erroneous as I pulled the pump and found tank & pump looking pristine (pump was replaced in April).
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