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Which OBD codes to work on first, and how?


rmasteller

New Member
Joined
Aug 1, 2020
Messages
6
Location
Central Ohio
Getting my LJ back on the road after it sat for a year waiting on a transmission rebuild. Finally did that last week and it's driving great. But, I've got a slew of OBD codes and I'd like some advice on what I should address first and how. Here's what my OBD reader says, in order:

2 Codes
P0440
P0440pd
MIL ON
Monitors
2 Inc
Evap
02 Htr
5 Ready
Misfire
Fuel
Comp
Catalyst
02 Snsr

Thanks in advance, TJ Forums!
 
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OP
rmasteller

rmasteller

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Central Ohio
Nice trick! I didn't know that procedure. It only shows P0440 then 'done'. So, I should just track down my evap issue? I believe the gas cap is a common issue causing that code, right? I think I bought one a year or two ago from a dealership for this same error code with no benefit. I'll search the garage and see if I still have it. I know some people have purchased a smoke generator so find cracks in lines, but the cap test will be first.
 
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pagrey

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Apr 10, 2018
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3,275
Location
Los Angeles, CA, USA
Ya, probably just an evap leak. You might check the vacuum lines around the intake manifold and the area around the purge solenoid. It think it's bolted on the driver fender somewhere on yours. Also take a look at the lines under the Jeep down by the gas tank on the drivers side. They sometimes leak there too.

Just so you know the evap code will clear by itself with one successful cold start. That's when it does the click click click pressure test you can hear by the rear passenger tire. So if the cap is the problem, let it sit overnight and then start it and let it idle for a minute or two. The light should clear if the leak is plugged.
 
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rmasteller

rmasteller

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I had P0440 a lot since purchasing the LJ back 4 - 5 years ago. No sign of a Mopar cap in the garage, but I know I've tried a different cap than came with it (cap that came with it had a tether, this one doesn't). Existing cap on it has an S logo.
20200801_192408.jpg
 

pagrey

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Location
Los Angeles, CA, USA
Stant locking cap. Plenty of people use them but it could be the problem. You can get a factory cap on ebay for under $20 shipped these days if you want to try that.
 
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rmasteller

rmasteller

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This may be a Mopar part! This one shows the same logo.

As does my local dealership's link to the Mopar catalog.

Well, here's a Stant one too that looks the same.

I'll get a genuine Mopar one, if that's the "go to" cap on these Jeeps for P0440.
 
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rmasteller

rmasteller

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Aug 1, 2020
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Location
Central Ohio
(y)

Why would the OBD reader give so much information compared to the technique using the odometer to display codes?
 
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rmasteller

rmasteller

New Member
Joined
Aug 1, 2020
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Central Ohio
So, that locking cap is Mopar. I thought I bought one to address an evap code. The gray noodle isn't total mush just yet!

20200802_090102.jpg
20200802_090109.jpg

My hood still has the emissions schematic sticker, so I traced lines and I see where all my evap devices are and how they're connected. Now it's just troubleshooting.

One more thing. My fuel filler neck has that problem where the flapper doesn't work right and the gas pump will overfill and spill fuel. Is that issue in any way related to evap codes?

Thanks!