Dodge Dakota - P0420 code

My 2005 Dodge Dokota 4.7L V8 152,000 miles has an intermitent check engine light (CEL) code P0420 (‘catalylst efficiency’) that turns itself off.

  1. 151,000 CEL on, code P0420, checked, cleared at dealer.
  2. 151,948 CEL on, code P0420, checked, cleared at dealer (Cat Conv est $800).
  3. 152,200 CEL on, code P0420, checked, cleared at local auto parts store.
  4. 152,597 CEL on. No checks.
  5. 152,815 CEL turned off on its own
  6. 152,849 CEL on. No checks.
  7. 153,137 CEL turned off on its own.

Twice in this time CEL has came on soon after a fill up from near empty.

Engine runs fine, 18-19 mpg highway.

Have seen numerous on-line reports of other possible causes:
a) base engine problems (coolant or oil) – coolant temp sensor
b) Air inleakage – air systems or manifold
c) Lazy front O2 sensor
d) fuel pumps
e) timing or misfire
f) what else? - (gas cap, other…)

Anyone have ideas on what to check first or categories to eliminate?


Weak fuel pump would result in hard starting and possible lean codes
A bad gas cap would result in an evap leak code
I’m almost certain that timing is not adjustable on your truck

A misfire can damage a cat

You never had any misfire codes?

You can check backpressure for bank 1 and compare it to backpressure for bank 2

If bank 1 backpressure is noticeably higher, chances are the cat is damaged/plugged

If the front O2 sensor is lazy, it may be switching slowly enough to generate P0420

Have the signals from the O2 sensors measured with a scope.

I’ll get those checked. If its an o2 sensor I may replace on my own. Parts are available; one had this in the description — "Note: You may be required to reset the vehicle’s computer after installation of this part."
What do I need to do that?
Thinking about buying a code scanner; are these capable of ‘reset’?

I saw on Wheeler Dealers TV show, they used Cataclean. This cleaned up their catalytic converter and O2 sensors.