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07:41:01 - 04/24/2024
V6 Dakotas
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andrew grant
Dodge Dakota
JOIN HERE
3/28/2008
11:21:12
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 Subject: P0420 code
IP: Logged
Message:
first of all, i have a 99 dakota, 3.9, 5 speed, 4x4.the check engine light came on and i scanned it and got code P0420, which, according to my book is "catalyst system efficiency below threshold(bank 1)" Now, does that mean the cat is bad, or maybe an o2 sensor, if it is a sensor, is it front or back?
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modain
GenIII
3/28/2008
13:14:41
|  RE: P0420 code
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Message:
It means the readings on the post-cat O2 sensor is too close to th readings of the pre-cat O2 sensor. So the PCM "thinks" the cat isn't cleaning up the exhaust as well as it should be doing.
The usual causes are:
. the cat is bad - needs replacement (expensive, do last)
. if you have changed the rear O2 sensor, but not the front one this code can easily pop up - the fix/solution is to replace the front O2 sensor whenever you change the rear O2 sensor. The PCM reacts badly when a new rear OS2 sensor is paired with an aging front O2 sensor.
I had this code pop up on my Toyota Avalon some time ago. It turned out from a sniff test that there was a lot of unburned HCs being measured. The first course of correction is a tune-up (new plugs, wires, etc.) It turns out these hadn't been changed in many-many miles. After I did a tune-up the HC number returned to good levels on the sniff test and the MIL code stayed off.
How old are your ignition components?
What's your left foot doing?
==============
2002 Graphite QC SLT Plus, 4.7L, NV3500, Superchips 3715, 3.92 LSD, R/T rear swaybar, no chrome, loads o'fun...
2001 Patriot Blue Durango SLT, 4.7L, 45RFE, Superchips 3715, 3.55 Open (for now)
1999 Forest Green Dakota RC Sport, 2.5L, NV1500, 3.55 Open
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andrew grant
Dodge Dakota
JOIN HERE
3/28/2008
13:26:52
| RE: P0420 code
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Message:
coil is brand new, wires look new, but i dont know that for sure, i havent checked the plugs, i'll do that soon. i pulled out the rear o2 sensor behind the cat, and it was very dirty, carbonish looking, i cleaned it and put it back in.the light stayed off for a day or so then came back on.
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modain
GenIII
3/29/2008
13:49:47
| RE: P0420 code
IP: Logged
Message:
The diagnostics procedures list the possible causes as: exhaust leak, engine mechanical problem, catalytic converter, upstream O2 sensor is older than downstream sensor.
You haven't stated how many miles are on the truck, but I would presume it's well over 100K. If these are the original sensors they should be replaced, as they are well past their expiration date. That way you know you have fresh/good sensors to work with.
What's your left foot doing?
==============
2002 Graphite QC SLT Plus, 4.7L, NV3500, Superchips 3715, 3.92 LSD, R/T rear swaybar, no chrome, loads o'fun...
2001 Patriot Blue Durango SLT, 4.7L, 45RFE, Superchips 3715, 3.55 Open (for now)
1999 Forest Green Dakota RC Sport, 2.5L, NV1500, 3.55 Open
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J and J Auto
GenII
4/02/2008
00:40:16
| RE: P0420 code
IP: Logged
Message:
o2 sensors gett lazy over time
converter has a 80,000 mile replacement dealer
go to ngk.com and get a good sensor same as
factory half the price
stay away from other sensors and if it does not
look the same as stock design do not use it
most parts houses sell sensors that are not
designed for the vehicle they will sell the
same sensor to cover a 1000 diff vehicles
do it right the first time with the right sensor
and you won't be doing it again in 20,000 miles
Larry
J&J Auto
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