Hello All - I've got a 99 Dakota with the 5.2 4x4 quadcab and just under 100k miles.
Let me put my question first so it doesn't get mixed in with the description of my problem.

My question is as to what the instrument cluster does with input readings...does it only take in readings from the rest of the truck to show them on the gauges, or does it then OUTPUT any of these readings to the main computer or indicator lights (meaning the check engine light)?

About a week ago I noticed the oil pressure riding very high (almost pegging to the right) while pulling into a parking lot. All the other readings were fine (tach/temp/etc) and continued to read ok while I sat with the engine idling. Pressure was still reading very high though. I keep a OBD scanner in the truck, and even though I know it won't show oil pressure, I hooked it up to see if I could see anything unusual. Everything was ok. So, stopped the engine, went and picked up some stuff I needed and came out about an hour later. When I came back and started the engine back up, everything read fine. Took it easy the couple miles home and no problems. The next day when I started up, oil pressure reading was way up again....
Anyways, this has gone on and off for the last week, but I don't drive it very much. Sometimes the pressure gauge reads high, sometimes not. Funny enough, it seems to read ok early in the morning when the cab is cooler, but in the late day when it's hot inside the cab it always seems to read high.
In the meantime I looked around and found the service manual links here in these forums (thanks!) for the 00 model and discovered you can do a diagnostic test on the instrument cluster.
The test gives two codes. 100, and 999. The 999 is a very generic ("something is broken") code, and the 100 indicates a problem with the CPU/EEPROM and the recommended action is replacement of the cluster.
I may hook a mech pressure gauge up to the engine just to make sure it's not also the sensor, but since I'm not getting any warning lights, scanner readings ok, and the cluster tests bad, I'm betting the sensor is good.

Ok, oil pressure is nice to know, but not life or death to me at the moment so I'd rather wait until a convenient time to change out the cluster. But if the cluster is sending this info out to the rest of the truck, and because of this I might eventually get some check engine/oil lights, I might be forced to do this quicker. So I'm trying to figure out if a bad cluster will lead to other problems because it's then spitting out bad info to the rest of the truck.

Guess I should throw out some final thoughts on the cluster....from reading here and other forums/locations, changing a cluster yourself may not always be a simple job? Not from the physical swap (that looks pretty easy), but first is, the mileage would have to be reprogrammed. My understanding is miles is not only stored in the cluster itself, but also (up to) two other location (computers) in the truck itself. Second, I read some references that the cluster has to (or should be) programmed with a DRBIII to match it with the options of the truck it's now in.

Bit of a long post...sorry. I tend to go into too much detail I guess. But many thanks for any comments and advice anyone can add.

 

The cluster is driven by inputs from the PCM. It does have an output the "check gauges" light.

It would be far more likely for the sender to be failing than it would the cluster. I'd check pressure with a gauge to be sure but in the meantime just change out the sensor. It's an easy test.

 

Ah, I see, so you're saying a bad input from the sensor itself could be throwing the cluster test itself? That seems a bit opposite from what the service manual states, but I agree that putting the mech gauge on won't take long. I just need to find mine now (or just go buy another one).

Good to know about the engine light possibility. I'm surprised it hasn't lit up yet. I can deal with that...just didn't want the reading going out to the truck computer and it shutting down the engine. Think I read somewhere that's a possibility if the sensor sends a low pressure signal out (lower than 7psi?). Not sure if it'd do the same with a high pressure sensor signal.

Thanks!

 

110 is the code for a bad eeprom/cpu/ram.

I wouldn't worry about that code unless you're having other issues. Check the pressure and go with the sensor first. It's mechanical and they can fail. How did the gauge sweep test work out?

I've never heard of a a low pressure signal shutting the engine down. That could be dangerous for one thing. It will trip the check gauges though. Not sure on the high.

 

Ah, sorry...I forgot to mention the dials when I did the test!

This probably sounds strange, but as I mentioned in my earlier post, the gauge seems to behave when it's cooler in the cab....and the same with the self test. If I do it early in the morning the pressure dial will stop at the correct locations (the low/high lines) but if it's warm/hot in the afternoon, the dial will stop at the middle, then again above the upper line....like the entire reading has been shifted over. Suppose back in the old days there'd be a coil spring of some sort that went bad but doubt with these new systems.

Guess I could just try putting a meat thermometer in the cab and see if I notice a relation to the inside temp and how much the gauge is off...

 

It sounds like you do have a cluster problem.

Yes another cluster will need to be programmed for your options. It's quick with the DRB. The odometer will read the new cluster mileage.