Check Gauges Light

I need help from someone knowledgeable reading this group.
2003 1500 2wd 5.7l Hemi. low mileage 48K, oil changes done at 3000 to 3500 or 6 mo which ever comes first.
Problem: Intermittent check gauges light upon starting, has no oil pressure reading on the gauge when this occurs. Shut it off wait 5 sec and start again oil pressure gauge registers pressure and no light. Hot, cold makes no difference
Could be bad sending unit but I would think bad unit would be more consistent in failure. I am leaning toward bad connection somewhere.
I have Factory Service Manual and know which pin and connector on the PCM the wire from Oil pressure sensor goes to but for the life of me can't find the output from the PCM to the instrument cluster or any of the gauges in the wiring diagrams for the instrument cluster so I can check the connectors for crud.
Any one got any other ideas and/or links to good wiring diagrams for instrument cluster?
Does Dash gauge really show Oil pressure or is it just a signal from the PCM that there is oil pressure?
I don't know if the sender is a switch or a variable resistor since it is a one wire (on a two pin connector) Diagram indicates its variable, I do know it should get 5V from the PCM. So is the PCM reading current flow or voltage drop?
I just found in the service manual that the oil pressure gauge gets its data via the PCI bus so now I know that the little 'puter in the PCM is talking to the little 'puter in the instrument cluster via the FCM. That about rules out a bad connection after the PCM since everything else seems to be working okay. (Yes I was reading while composing this, It some times helps me to sort out the solution to a problem to work that way.)
I think I'll try a meter on the sender for ohms engine off then running and see what the difference is I don't want to spent 30 bucks for a part and not have it fix the problem.
TIA
Happy Camping. snipped-for-privacy@NOPANTS.juno.com Remove NOPANTS To reply by direct E-Mail;
2003 Dodge 1500 QC SB Hemi, A/T, Tow Package, 3.92 gears (11 mpg Towing) 2001 Aerolite 21RDB 21ft TT (Scales 2900 dry)
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If you want to make this easy you could just put a new sending unit it and be done with it. You've just described a defective sending unit.
Denny
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wrote:

I lived with the problem until yesterday when I had to have my mandatory State Inspection. Well it is not the sending unit, shop did mechanical pressure gauge check, Oil pressure was good at start. They put a new sender in and problem remained. I did a Instrument Cluster self diagnoses and got an AA code so Monday 8/1 it goes to the Dodge dealer for PCM diagnoses. Happy Camping. snipped-for-privacy@NOPANTS.juno.com Remove NOPANTS To reply by direct E-Mail;
2003 Dodge 1500 QC SB Hemi, A/T, Tow Package, 3.92 gears (11 mpg Towing) 2001 Aerolite 21RDB 21ft TT (Scales 2900 dry)
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On 7/27/2011 10:19 AM, Thats Me wrote:

Silly things... My 2004 has done the same thing, but eventually it stopped doing it. It always would 'go away' if I shut down and restarted the engine. (and it always did truly have good oil pressure, so it is/was a dash-cluster/PCM problem.
But I've not had an occurrence of the problem in at least a year, so I'm thinking it won't be back.
--
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Suddenly, without warning, PeterD exclaimed (7/27/2011 1:02 PM):

Have you checked your truck for codes recently? My truck was acting fine, but a random check for codes using the on-off-on-off-on method threw a code that indicated the PCM had died.
Heh. The first shop I took it to went on and on about how hard the PCM is to get to in my truck, it would cost tons for labor, yadda yadda...
I looked it up in my service manual, in the 2001 Dakota it's right on the firewall. I could have replaced it myself, if I knew how to get a properly programmed one. Took it to Dodge, the PCM cost a lot but only took about 15 minutes to replace.
The only difference I noticed in my truck between "dead PCM" and "new PCM" was my gas mileage improved significantly.
jmc
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How much for the part?
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Suddenly, without warning, NotMe exclaimed (7/31/2011 2:30 AM):

I can't remember but I think it was around $800. Not cheap!
jmc
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wrote:

What kind of noise did it make when it died?
beekeep
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Suddenly, without warning, beekeep exclaimed (7/31/2011 7:49 AM):

No idea. I didn't even know it was dead. I just sometimes randomly check for codes when I think about it (well, it IS 10 years old). Zombie Truck for some unknown length of time - it was brain dead but still doing it's job :)
jmc
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On 7/30/2011 6:25 PM, jmc wrote:

Good thought, perhaps I was not totally clear, but the check gauges warning would come one, and the oil pressure gauge would read zero. So the check gauges warning was valid, but the oil pressure gauge was reading incorrectly.
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Just got back from the Dodge Dealer, wallet is $160 lighter. But I got oil pressure reading on the gauge upon initial start now.
PCM was good, Instrument Cluster was good, oil pressure Sender/Switch was good. Problem turned out to be a bad connector at the Oil Pressure switch. Don't know exactly how they repaired it, but its got a 12mo/12k mi warranty.
$80 bucks to diagnose the problem, (Flat fee to read the codes and the TS manual). $65 Labor and $15 for shop supplies and tax.
I'll go out later and look to see if wire was replaced and spliced or if connector was "adjusted".
Happy Camping. snipped-for-privacy@NOPANTS.juno.com Remove NOPANTS To reply by direct E-Mail;
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On 3/25/2011 12:58 AM, Thats Me wrote:

At least don't feel alone! My 2004 Hemi does exactly the same thing. Only once every few months, and not in the last six months... Did (when still under warranty) take it to the dealer, but they did nothing as it was OK then.
Same situation: start, no OP reading, and a Check Gauges light. Shut down, and restart, and all was well. I know it had oil pressure, just was not reading.
Because my problem kinda went away, I'm not trying to fix it yet.
And yes, the sender is analog, the computer interprets that and drives the OP gauge. If any gauge is out of bounds the "Check gauges" (or whatever it says...) light is turned on and it bongs to get your attention. (This happens when the battery voltage is too low, temp too high, etc.) The "check gauges" light will turn off if the gauge returns to a 'normal' reading as well. Does not require shutoff, it is dynamic.
Oh, and never had it start reading right unless I shut down either.
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