code p0420 after messing with horn

[ayagle]

I got the check engine light soon after replacing my horn.. I was trying to find a place to put the replacement horn, and I was shifting it around under the battery, it's just a single horn so it was easy to shift around to different areas

there are vacuum lines going to a valve of some sort under the battery there near the horn, I was curious if I may have messed up a dry rotting large vacuum hose that goes down to that module, or something else to do with that 'module' or whatever it is, (what is it??) does it have anything to do with the hubs?.. it seems I have had clicking from the hubs or a bad axle since about that same time.. but the cel code came up after I put in the replacement horn.

I've only had the explorer for about 3 months, so, Idk if its possible that the timing could be a coincidence and it has bad rings or seals or something and now I have bad cats. or something like that.,

I did replace the plugs and stuff to try to tune it up, (I read it could be because of a miss or just bad running in general). I have also recently changed the oil, before the code came up, when I first noticed the check engine light, I checked the oil and it was a bit low, I thought that might have something to do with it, but apparently not. I have also flushed/replaced the coolant. (after the cel code).. I can't seem to find a vacuum leak though if that is what caused it, from my fumbling around under the battery.

Thanks for any assistance any one can provide

sorry if this is horribly written. English IS my first language, but I'm just horribly 'slow'.. I'm not sure if I am missing vital info, or whatever, I hope it makes sense.. :scratch:

 

[2000StreetRod]

fuel vapor management valve

The module on the driver side below the battery tray is the fuel vapor management valve and I doubt has anything to do with your diagnostic trouble code.
P0420 Catalyst System Efficiency Below Threshold (Bank 1)
Here's a link to a helpful article: The Misleading Nature of the PO42O Code

 

[ayagle]

I appreciate the response, I know it has been a while. Could you possibly tell me what that hose might be called?.. it has a quick connect on either end, I am thinking that it may be the problem. especially if it has to do with emissions. from what I understand anyway. Thanks again

 

[2000StreetRod]

which engine do you have?

There were three possible Explorer engines in 1998: 4.0L OHV V6, 4.0L SOHC V6, and 5.0L V8.

Is this the "module" you're asking about?

 

[ayagle]

Yes, that is the one, just behind the fender under the battery on the drivers side.. I have the 5.0. The biggest line that goes to the intake is really dry rotted, so I figure I might have put a leak in it, or possibly messed up that module or unplugged it or something.. I just haven't had any time to take out the battery and inspect everything. I guess I'm worried I will mess it up worse before I have the parts.. Thanks

 

[lobo411]

As 2000rod says, it's probably a coincidence that the code came up when you worked on the horn. My two suspects would be the o2 sensors and the DPFE sensor. I used to get that code all the time and I replaced the above, and it hasn't been back in 5 years.

The o2 sensors are supposed to be replaced every 100k, and the original DPFE sensor design is defective so it's going to have to be replaced too at some point.

The DPFE is the easiest to replace so I'd start there. The DPFE looks like a 2" x 4" box attached to the upper intake manifold, with two vacuum lines running out the bottom and going to the metal EGR line. If the sensor is metal/aluminum, it's one of the bad ones. IIRC, the DPFE was what solved my problem. $30, 5 min job.

This is on a 4.0 OHV.

 

[chefduane]

Ditto lobo's comments on the DPFE sensor. I had to replace the EGR valve on my 4.0L SOHC and broke off one of the hose nipples on the DPFE. Bummer. Mine was about
$50. Took 10 mins to replace it. Worst part was I had to drive my wife's POS Trailblazer to Autozone to get it.

 

[ayagle]

You may be right about that, I took the battery out, and checked all the hoses and the dpfe sensor you mentioned, seems that is a hard place to fit on a vacuum hose, so the previous owner cut the end of the hose. It must have slipped off just enough to leak when I did the coolant change or something..

the cel hasn't come back on since clearing with the removal of the battery so I am assuming that must have been it..

Thanks again..