JeepGirl42

Hello,
i have a 2001 Jeep Cherokee. I've been having Jeep troubles and I don't know what to do.
First: My check engine light is on (Code P0455)
And when I'm stopped at a light my check gauges light comes on and my oil pressure goes down.
I've changed my fuel cap and I changed the canister purge valve solenoid. Im assuming this is not something that I could fix myself since I'm not handy. But before I take her in . I want to have an idea what's wrong so I'm not charged for stuff i don't need.

4.3L XJ

Welcome Jeep Girl

OK, you got the large leak code. Was your gas cap loose? If so, eve for a short time, it will cause that code to appear. Another possibility is a cracked or loose hose on the fuel system. Take your battery cables off, touch them together and put them back. See if your code reappears.

JeepGirl42

Thank you. When it first came on, I went to O'Riley and the guy suggested I replace the gas cap. I bought one from th dealership. It's still on. I bought a obd scanner and I turned it off but it keeps coming back on.

CurrySoSpicy

You wouldn’t happen to be running low on coolant every once in while and having to add more?

extrashaky

This:

And this:

Are two different problems.

The P0455 code is telling you that you have a vacuum leak somewhere in the evap system. It has nothing to do with the oil pressure gauge. If the leak can't be found through visual inspection, it may need to be located using a smoke test, where smoke is pumped into the vacuum lines to see where it escapes.

The oil pressure light coming on is unrelated to the evap leak and means one of two things. Either you actually have low oil pressure, or your oil pressure is fine and you have a bad sending unit (AKA sensor, sender). The way you test this is to put a mechanical gauge on the motor and see what it says the pressure is. If the pressure is good when tested with the mechanical gauge, you replace the sending unit.

If the mechanical gauge reads low oil pressure, then you know you have an engine problem. It could be as simple as needing a new oil pump. However, your year has the 0331 cylinder head that has a known issue of cracking and leaking coolant into the oil. Once coolant gets into the oil, it starts eating the bearings. When the cam bearings go, your real oil pressure will drop to zero at hot idle. That's why Curry asked you up above if you were having to top off your coolant periodically, because disappearing coolant is a potential sign of the head crack, and disappearing coolant for a while followed by low oil pressure can be a sign that the cam bearings are trashed.

So unfortunately it's not as simple as I suspect you were hoping. Your repair could range from just swapping a sensor to an engine overhaul or replacement, and unless you're willing to dig into it and diagnose it yourself, you're going to be at the mercy of your mechanic to determine what it actually needs.

Checking the oil pressure with a mechanical gauge and changing the sending unit (if it's bad) is something you can do fairly easily yourself if you want to learn. You can actually borrow the oil pressure test kit from Auto Zone for free. All you do is unscrew the sender, screw the manual gauge in its place and read off the number to see if it's dropping to zero. Here's a video showing how to replace the sender, but you can also see where you would screw in the mechanical gauge to test the pressure first.