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Intermittent P0420 code


Vindictus

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This started Monday night. Out to the store and CEL came on. I rest it, went to work Tuesday (60 miles) all was good. Went out after work it came on again. reset it and came on, on my way home to night. I replaced both cat's and O2 censors about 3 years ago. O2's are motorcraft cat's are from Eastern Catalytic. Shouldn't they last longer?? Could anything else besides a bad cat cause this? Like an exhaust leak of some kind? Thanks everyone
 


Craig0320

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Break it right the first time. Fix it better the next time.
Check your rear o2 sensors on a scanner and they should be mostly solid non moving if you have a good functioning set of cats. In park at operating temperature have the engine at a constant 2000 rpms. Using a digital thermometer take the inlet cat temp and the exit cat temp. The temperature should be hotter coming out the back by at least 200 degrees even a little less won't through a code. This lets you know the cat is doing what it's supposed too.
 

Vindictus

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Location
NewBrunswick Canada
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Ford Ranger
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4.0 V6
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ReMan 4.0 SOHC
Transmission
Manual
2WD / 4WD
2WD
Tire Size
235/75/15
Check your rear o2 sensors on a scanner and they should be mostly solid non moving if you have a good functioning set of cats. In park at operating temperature have the engine at a constant 2000 rpms. Using a digital thermometer take the inlet cat temp and the exit cat temp. The temperature should be hotter coming out the back by at least 200 degrees even a little less won't through a code. This lets you know the cat is doing what it's supposed too.
I did check them with my scanner and they are not moving very much. My scanner is showing both cat's almost identical temp's. I'll bring a temp gun home from work and check this weekend. Thanks for the help
 

Vindictus

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Location
NewBrunswick Canada
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Engine Type
4.0 V6
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ReMan 4.0 SOHC
Transmission
Manual
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2WD
Tire Size
235/75/15

Vindictus

Well-Known Member
Joined
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287
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Location
NewBrunswick Canada
Vehicle Year
2011
Make / Model
Ford Ranger
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4.0 V6
Engine Size
ReMan 4.0 SOHC
Transmission
Manual
2WD / 4WD
2WD
Tire Size
235/75/15
I had a chance to look at this p0420 code some more. Code reader list these as possible causes.
Incorrect fuel grade used
fault Bank 1 Sensor 1 Oxygen sensor
Fault Bank 1 Sensor 2 Oxygen sensor
Faulty Engine Coolant Temperature (ECT) sensor
Damaged or Leaking exhaust system
Excessively retarded spark timing

Why can't it be easy o_O
 

Vindictus

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Location
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ReMan 4.0 SOHC
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2WD / 4WD
2WD
Tire Size
235/75/15
Changed O2 sensors and CEL still throws 420 code. I will check inlet and outlet temps of cat when i get to work in the morning
 

Vindictus

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Location
NewBrunswick Canada
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2011
Make / Model
Ford Ranger
Engine Type
4.0 V6
Engine Size
ReMan 4.0 SOHC
Transmission
Manual
2WD / 4WD
2WD
Tire Size
235/75/15
Check your rear o2 sensors on a scanner and they should be mostly solid non moving if you have a good functioning set of cats. In park at operating temperature have the engine at a constant 2000 rpms. Using a digital thermometer take the inlet cat temp and the exit cat temp. The temperature should be hotter coming out the back by at least 200 degrees even a little less won't through a code. This lets you know the cat is doing what it's supposed too.
I checked my cat's temp's this morning. The inlet temp is 445F the outlet temp is 285F with a difference of 160F so looks like I need a new cat :( I wonder if it's worth doing warranty through rockauto?
 

Craig0320

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Make / Model
Ford
Engine Type
V8
Engine Size
5.0
Transmission
Automatic
2WD / 4WD
4WD
My credo
Break it right the first time. Fix it better the next time.
I would reach out to them first. That is definitely not doing it's job effectively.
 

19Walt93

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My credo
If you don't have time to do it right will you have time to do it over?
First, the "rear O2", isn't an oxygen sensor, it's called a cat monitor. Ask an experienced Ford counterman for a rear O2 and he'll look at you like you're an idiot. I agree with trying the cheap stuff first but I have never seen a PO420 fixed by replacing anything but a cat. We replaced darn few, almost exclusively with OEM parts or Walker direct fit cats if the customer gasped at the OEM price.
 

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