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P0402 and P0420 Now what?

9

96SEBlack

CEG'er
Joined
Oct 20, 2003
Messages
55
Location
KS
OK, this project has been long overdue and the CEL has been on way too long and sorry this thread is so long-winded. I started out with 7 codes:

P0171 Too Lean Bank 1
P0153 Bank 2 Sensor 1 Slow
P0401 EGR Insufficient Flow
P1150 O2 Sensor Bank 2
P1151 O2 Sensor Lean Bank 2
P0151 Bank 2 Sensor 1 Low Voltage
P0174 Too Lean Bank 2

What I've done so far:
Seafoam gas, oil, intake through brake booster line, let set 30min
(Some smoke, but not as much as I expected)
Replaced both upstream O2 sensors (pain in the a$$)
PCV Valve
Fuel Filter
Oil/Filter, Air Filter
Cleaned MAF Sensor
Reset Codes

Got rid of 7, now have 2 new codes:
P0402 EGR Excessive Flow
P0420 Catalyst System Efficiency Below Threshold (Bank 1)

The DPFE is the original metal and I plan on replacing soon with the updated plastic sensor. This should get rid of P0402 I think, but why did the code change from Insufficient P0401 to Excessive P0402? And why P0420 now out of the blue?

What I did tonight:
Did the suck test on the EGR valve and it idles rough, but I can't make it die
Added 3/4 can of seafoam to 1/4 tank of gas
More seafoam through BOTH intake lines, let set 1hr
Reset Codes
A LOT more smoke this time from seafoam

My thought is this might clean up the precats and get rid of P0420.

BUT, If P0420 comes back, which it probably will, what would you do next?
Downstream O2 sensors?
Clean UIM and LIM?
Replace cats? (rather not)
Gut precats?
MIL eliminators (rather not as it's gone 198K just fine without them so far)
Reprogram at a dealer so P0420/P0430 faults aren't so sensitive?

Thanks for any suggestions.
 
Less than 10miles after reset and both codes are back.

Thinking about swapping rear sensors to see if the P0420 turns to P0430 then I know it's a bad sensor...sounds easy enough.

P0420 is the one that worries me, any suggestions? Anyone?
 
The 420 is a such a vague code that a lot of things can trigger it. Running seafoam through the cats isnt going to do anything good for your precats so I'd just add a anti-fouler to each lower sensor and see what happens. Also when you say you reset the codes what exactly do you mean?
 
IMO, MIL eliminators are a last resort . start with swapping the sensors and see if the code follows, even if it doesnt i would be tempted to replace both O2 sensors anyways. then if your still getting the code with new sensors either gut the manifolds or install headers, and install MIL eliminators then.
 
Yeah, from what I've searched here P0420 is vague and any one of the things I've listed have fixed it for some. "Anti-fouler"? Is that the same as MIL eliminator?

Reset....clearing the codes with a code scanner so the CEL goes off. Same thing as disconnecting the negative battery terminal for 10min or so.

The downstream sensors are soaking in PB Blaster right now. I'll try to swap them later tonight or tomorrow and see what happens.

Thanks for the input!
 
Anti-foulers are spark plug anti-foulers that you use as a spacer for the sensor and usually it moves it just enough to fake the signal out enough to stop the codes.
 
Like pretty much everyone else that owns a V6 i too had a P0420 on/off for a couple of years. Replacing the O2 sensor did nothing and a UIM / LIM , TB cleaning also did nothing. Installing $3 dollar O2 extender got rid of the code for good.

You can get 2 extenders on ebay for about $10 delivered. I'd do that first before wasting money replacing 02 sensors that may still be perfectly good.
 
0420

0420

Before taking the time to swap O2 sensors look at what Ford has to say about the P0420 code. People tend to think the 0420 code means the O2 sensor is shot. Not typically the case. First items on the trouble shoot list is to check the engine coolant temp sensor. This tells the comp how the hot the coolant is. (this is not the sensor for the dash gauge) The temp is very important to fuel trim ect. Although installing the anti fouler may take care of the code it may not be the best for engine performance. The ECT is cheap and easy to change. Follow the trouble shooting guide will hopefully cure the problem and improve performance of your engine. If the trouble shooting items are explored but do not correct the problem then look at the anti fouler fix. Good Luck Dan PS. It is not recommended to try and clean O2 sensors. Not sure if manufacture wants to sell sensors or it truly is not good for the sensor.

CATALYST EFFICIENCY MONITOR
Diagnostic Trouble Code Description Possible Causes
P0420 - Catalyst System Efficiency Below Threshold (Bank 1) Indicates Bank 1 catalyst system efficiency is below the acceptable threshold. ·
Malfunctioning Engine Coolant temp sensor
· High fuel pressure
· Damaged exhaust manifold
· Cylinder misfiring
· HO2S wiring concerns (shorted or chafed, bent pins, etc.)
· Damaged exhaust system pipe
· Damaged muffler/tailpipe assembly
· Retarded spark timing
Damaged Catalytic Converter:
· Use of leaded fuel
· Oil contamination/consumption
· Silicone contamination (sealants/cleaners
 
I don't think I'd be putting an O2 sensor in anything to clean it, once it gets hot whatever on it will bake on.
 
"· HO2S wiring concerns (shorted or chafed, bent pins, etc.)"

I started to swap sensors and noticed the rear downstream connector had brittle missing insulation around the 4 wires and was kinked. More fell off as I moved it around. This is the connector that stays with the car, not the sensor side. So a little electrical tape and a dab of silicone and I put it all back together.

CEL came on with both codes again about 25mi later.

Where is the ECT (engine coolant temperature) sensor and is there a way to test it? I'm assuming by the firewall, but I don't really know what I'm looking for.
Thanks
 
Thanks Tony.

P0420 may be gone...
I swapped downstream sensors for kicks. This time I cleared codes, drove it, checked pending codes, P0402 and P0420. Shut it off, cleared codes again, drove it, shut if off a few more times, let it idle, etc and now have P0402 and P0136/P0156 - Bank 1 and 2 Sensor 2 O2 Circuit Malfunction.

Even though I cleared codes with the scanner, maybe I wasn't letting it warm up enough and get clear through the OBDII drive cycle before? IDK

Anyway, I'll keep driving it and checking codes to see if they change or throw new codes.

Checked #13 fuse for the HEGO sensor circuit and it wasn't blown, but changed it anyway...don't think that's the problem.
 
96SEBlack said:
...P0136/P0156 - Bank 1 and 2 Sensor 2 O2 Circuit Malfunction.

...
Click to expand...
If you have electronic mileliminators, maybe the connection or connectors are broken. If not, then you have a wiring harness problem relating to the Lower O2 sensor.
 
No MIL eliminators here and P0420 is back along with P0136, P0156 and P0402. Downstream O2 sensors have 100K+ on them and may be originals for all I know. An O2 sensor and catalyst recall work was done soon after we bought it at 50K miles to get rid of CEL, but I don't know exactly what was done then.

Another round of parts will hopefully get rid of codes and the engine/emissions should be in good shape except for oil leaks...a project for later. I plan on ordering DPFE sensor for P0402, ECT sensor and downstream O2 sensors with antifoulers/extenders for P0136, P0156, P0420. Unrelated, but will also need serpentine belt and cabin air filter.

Thanks for all the input, I'll let you know how it turns out.

PS: Before any of this, I was consistantly getting 22-24mpg. Haven't gone through a full tank yet, but so far it looks to be getting the best mpg ever with what I've done to this point (seafoam, upstream O2's, fuel filter, air filter, PCV, oil and filter, cleaned MAF sensor).
 
A quick question about antifoulers on ebay. Some have a compression washer, most have a tapered seat. Some are 318 or 304 stainless which I think would be good, but dont know if it's necessary or just hype since the exhaust it's going into is not stainless. Most are zinc plated.

Does it really matter?
 
The only ones I've ever used were the washer type just like the sensor that it replaces but I think most people just use the standard 42002 package.
 
All my parts should finally be delivered tomorrow...DPFE sensor, downstream O2 sensors, ect sensor and anti-foulers.

My first thought was to install all parts including anti-foulers and be done, thinking they might give an added bonus of better mpg and protecting O2 sensors by moving them out of the airstream, whether they are needed or not.

But I'm having second thoughts on the anti-foulers. Should I install them or leave them off and see if the other parts get rid of codes first?

Put another way, is there any benefit (or potential harm) from installing anti-foulers on a stock car with no CEL?
 
199K no CEL!

199K no CEL!

To put an end to this thread...tonight I put in a new DPFE sensor, ECT sensor and 2 downstream O2 sensors with anti-foulers. Drove it through the drive cycle, let it idle, turned the key off and on several times...etc, checked with my scanner...no codes, pending codes or CEL and lights up the "green check mark" on the scanner!

This site is great, there's a ton of valuable info here, keep it up and thanks again for everyone's input!
 
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