96 XLT 4.0L - Error code 401 and 420

[RedBeard]

1996 XLT 4dr 4WD 4.0L OHV - Error code 401 and 420

Long story short...

CEL is steady on. Bought a scanner, got codes 401 and 420.

401 - Insufficient EGR Flow detected
420 - Catalyst efficiency monitor and/or exhaust system fault

Code 401 is easy... clean or replace EGR valve. Code 420 is a little vague.

Is code 420 just a generic trouble that's directly related to code 401?

BTW, I've been lurking here since I bought my '96 XLT in early April '02. I am amazed at the knowledge and support in these forums! Thank you so much to ALL of you who selflessly answer newbie questions like mine!

-RB

 

[Jason_25]

Yeah I think the code 420 definitely has something to do with the EGR system. Mine did the same thing. But before you go replacing the EGR valve, check the DPFE sensor first to make sure it's still good.

 

[Stephen S]

Welcome to the boards!!!

Could it be a bad O2 sensor(s)?? I read around here that when those go bad, they can cause all kinds of problems. Only trouble is, they are a little expensive to change if they really aren't the problem.

 

[RedBeard]

Jason... The thing is, I couldn't find the DPFE! The diagrams in my Chiltons manual are dense in this area, and there are no actual pictures of this sensor.

I did take some close up pics of my engine... If anyone can point it out, I'd be forever in you debt (well, almost).

Dig this...

Dead Link Removed

I think it is the one that I circled. Or is it the "X"??

I didn't get any codes relating to HO2Sensors. I am waiting to see if the CEL stays off after I replace the EGR valve and reset the computer.

Thanks in advance!

-RB

 

[Jason_25]

The X is the DPFE sensor.

 

[RedBeard]

Jason, you're the best. Thanks a million!

Note to Chilton's: AAAAAARRRRRGGGHHHH!!!!!

Tantrum over.

-RB

 

[RedBeard]

Can't remove rusty old EGR Vavle

The EGR valve is old and rusty. The two 10mm bolts at the flange are no problem, it's the 1 inch pipe fitting that's stuck. I've used a half can of WD40 on it (does penetrating oil ever work?) and I've heated it with a torch. I don't want to crank on it too hard because I don't want to rip the pipes open.

My X's computer is throwing code 401 repeatedly. If I take it to the dealer, and they crank on it to the point of breaking something... will THEY be liable for the breakage, or me?

Any hints or ideas?

-RB

BTW, DPFE Sensor test was OK per the Chilton's manual.

 

[Robb]

I've used a half can of WD40 on it (does penetrating oil ever work?)

It's only my experience, but WD-40 is the worst. I use this stuff called Kroil. Not sure where to find it. The last couple of cans I have had, I have gotten online. The can says it 100% gaurantees to loosen anything, I don't know about that, but in the probably 200 times I have used it, it has let me down 3 times.

Just throwing 2/5 of my nickel.

Robb

 

[Jason_25]

Have you tried to get a puller tool around it?

 

[RedBeard]

Puller tool for a pipe fitting? Sounds interesting... Do tell...

-RB

 

[origairbull]

fixed my 420 code!

I have had a 420 code for about a year now. First changed the O2 sensors and is was good for about one month, then came back. Cleaned and checked everything, but it would still come back in a month or earlier. Noticed on my computer that the rear O2 sensor was acting flaky, so I reinstalled the original, but it would fail a lot more often..... Well soon after I got a bad miss, so I replaced my fairly new BOSCH Wires and Plugs with OEM Motorcraft. Now, even with the original O2 sensor installed, I haven't had a check engine light in over 3 months, and about 1500 miles!! Started thinking back and realized it was about the same time I installed the BOSCH parts, I started having the problems.. And to think I was just about to replace the CAT system!

 

[origairbull]

420 code

I forgot to tell you I have a 96 4.0L with a 5 speed, 118,000 miles

 

[Glacier991]

The EGR code and advice regarding the DPFE are right on. It doesn't HAVE to be a DPFE problem, just usually is. remember the CEL [MIL] codes are really SYSTEM codes... do not take them too literally. The Cat monitor is a non continuous (which means the computer tests it from time to time) code that says when the computer does certain things to the fuel, and watches the pre cat 02 sensor and the post cat sensor, it gets readings that are not what it expects. It can be an 02 sensor, or a cat. Go slowly, do not rush out and start replacing 0 sensors.... sure it MIGHT be the prob, but at $75 a pop let us help!

Happy Exploring

Chris

 

[origairbull]

401 & 402

I also had both 401 & 402 codes and it was the DPFE; they never returned. The EGR valve is easy to check, there's only two ways it can be bad. Either it's stuck (open or close), or the diaphram has a hole in it and it won't operate because of that. The 420 code is set because the O2 sensors before and aft of the CAT are reading too close to one another, showing the CAT is not working properly. Other things may also cause this like low ignition timing (gases don't burn properly) and as I mentioned above, spark plugs and wires. Of course te CAT could be bad or the O2 sensors. Also keep in mind that the 96 explorers have a bulletin out calling or a reprogram of the computer to help solve bogus 420 codes. That was going to be my next step, but I'm good now!

 

[drummergirl]

bulletin?

I've got a 420 code on my '96 XLT..... what is this about a bulletin calling for reprogramming of the computer to eliminate bogus 420 codes? Where can I find out about that?

I'd be really really happy if it is bogus and not the CAT, but the darn CEL light is really really annoying!

Thanks!

 

[origairbull]

service bulletin

There was a service bulletin put out to reprogram the computer, but Ford won't do it for free. My friend also has a 96 XLT and it had the 420. Ford replaced the rear O2 sensor and reprogrammed.... So far it hasn't returned. Mine is going great also, and like I said, I replaced my plugs and wires with Motorcraft.

 

[origairbull]

3000 more miles and still no 420 code!

If you read my other posts, I changed my plugs and wires from BOSCH to motorcraft and no 420 code! It's been almost 5000 miles and 8 months.