jeep58

My jeep always reads 45psi on oil gauge does not matter if hot or cold and does not fluctuate when driving, always been like like this since purchasing jeep in September. A bad sending unit?

Noah911

This is an interesting topic and I will explain it how I know it best.

Your oil pressure gauge is a dummy if it goes to the same position and does not ever move. It is a dummy if the oil pressure reads at this same set level when only just turning the ignition key to run (with engine still remaining off.. Lol). It is a dummy if the gauge itself has only hashes and lines with no numbers on it. It is a dummy if the oil pressure sender unit near to the oil filter only has two wires (not three) coming from off it.

It is also a dummy if you have a 2003 or 2004 model year. The PCM interface to/with the oil sender unit is different and makes installing a three wire sender unit not backwards compatible if you were thinking to try and make your oil pressure gauge smarter...

Some 2002 model years may, and others may not have a smart oil pressure gauge.

There are rumors that some of the overlands and very few of the late model year limited editions did actually get a smart oil pressure gauge.. but, these special few will still only have the dummy hashes and lines with no real numbers to read on the gauge itself, just like the dumb ones.

Noah911

I almost forgot one of the most important things.

There is an impostor of the bunch. Some of the dumb ones fancied themselves with smart numbers on their gauges. They do not need those numbers.

In a way kind of like how maybe a non-smart human may wear glasses to try and make themselves look somewhat smarter.

Noah911

The oil pressure gauge and its sender unit was the first thing that brought me here to this forum to look up and find information on it.. just after getting into my 2004 WJ a couple of years ago. My new WJ made a dinging noise and it lost oil pressure showing zero on the gauge. It freaked me out for a second when it happened. Less than 30 seconds later it went straight back to about the mid-hash level mark. It did not do it again for a long time maybe almost a year or so.. and I had initially read all about how my 2004 model year Grand Cherokee comes with a dummy oil pressure gauge.

About a year into owning and driving my WJ it did it again. It was still kind of scary seeing zero oil pressure happen like that. It came straight back to halfway within a few seconds. From there, it began to do this several times a month. It progressed to happening several times a week. Finally, it would drop to zero several times every time I drove it...

This was how the oil pressure sender unit failed in my 2004 WJ. One day it never went back to halfway and just stuck itself at zero. I picked up a new generic oil sender unit from the parts store where I was at a few hundred miles away from home. I installed the new oil sender in my WJ in their parking lot. It has worked perfectly the same always at the same spot on the gauge for thousands of miles.

I am still shocked at myself for procrastinating such a long time to fix it. I guess I had gotten used to seeing absolutely no oil pressure all of the time?

jeep58

So the gauge is working ok? I mean it never really moves unless you shut the jeep down it will read zero and after starting the jeep back up it will a little under the line after the midway line on gauge, and it does not move when you race up the engine.

Noah911

Perfectly normal for it to behave this way how yours is doing on a 2004 WJ. It will drop to zero and make a dinging noise at a certain threshold psi. It will also drop to a zero reading and start to make a dinging noise whenever the oil pressure sender unit itself begins to fail and is malfunctioning.

It is not a true representation of the engine oil pressure in either case though...

Noah911

Oh, I almost forgot. It will also produce a visual cue for you too.

If the oil psi reaches its threshold limit to sound the alarm.. It will make a dinging noise, the gauge reading will drop to zero, and the mirror will display a message for you to check your gauges.

It does these same three things whenever the oil pressure sending unit begins to malfunction as well.

jeep58

Thank You !!

Noah911

You bet! I guess it has been awhile since I was last in the WJ, because the WJ mirror does not display information if I recall..

It is actually the little display above the mirror with the temperature, mileage, service interval, etc...This overhead is what would display a check gauges message for you if the oil psi sender senses a low oil psi (or, when the sender unit malfunctions).

dave1123

I'd like to add that the oil pressure sender in your 04 WJ is just a slide switch and not an actual pressure sensor. It will read 40 psi whenever there is oil pressure and zero if there isn't. I found this information on wjjeeps.com in the description of changes in the model years. I needed a sensor for my 00 WJ and got one from NAPA. It only read 40 psi ever. Then I got one from a dealer for my year and it read properly. Go figure. I asked the parts guy why they didn't just put an idiot light in the later models and he said Chrysler cars always sold well because they had a full set of gauges and the engineers figured they'd lose sales. Sounds stupid, but that's what he told me.

Besides that, on the WJ with the Can-Bus system, all signals from the sensors go directly to the PCM to be interpreted, then sent to the gauges. A "ding" and drop to zero with a "check gauges"light is just a loose connection. Usually. Except for when the oil pump dies! As mine did. But that's a story of another day.

jeep58

Good Information Thanks again !!