08 Dodge ram
I just need the truck fixed and was willing to pay to get it fixed but I find it hard to believe that everything I have change are all bad parts. I'm lost any help or guidance would be greatly appreciated thank you.
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Cheryl had suggested going for codes first, which I totally agree with. Get the truck to go into limp home mode again, and see what trouble codes are stored. Something as simple as an ELM327 Bluetooth device with your phone would work. I bought this BAFX one off Amazon , and it's worked very well.
The oil pressure gauge and code are interesting... I have to wonder if the PCM you bought is incorrect for the truck, OR the programming isn't correct. Some voltage measurements at the oil pressure sensor could help answer those questions. For reference, I looked up the wiring diagram:
Backprobing with the key on, we're looking for 5V on the pink/yellow wire, something between .5V and 4.5V on the violet/grey wire, and 0V on the dark blue/dark green. Or with the sensor disconnected and the key on, 5V on the pink/yellow, 5V on the violet/grey, and 0V on the dark blue/dark green. Let us know what you find.
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- cheryl hartkorn
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- cheryl hartkorn
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Do you still have the old PCM? Even if you end up causing a SKIM issue, I'd be interested to know if the old PCM produces the same high voltage.
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Jlr022581 wrote: From my understanding if it was a short to ground I wouldn't have a signal. But what about a high reading.
It's very unusual...Either the 5V regulator in the PCM is toast, there's a PCM ground issue, or another circuit is bleeding voltage into the reference circuit. I'll need to get home and have another look at the diagram.
Just to be clear, the oil pressure gauge weirdness wasn't there prior to the PCM replacement?
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For me, you've got two directions you can go. One would be to verify PCM grounds. The other would be to eliminate the 5V reference circuit as the source of the elevated voltage. We may end up doing both, depending on what you find.
Chrysler OE diagrams are nice, in that they condense PCM powers and grounds onto one page for easy testing. Check out the first page of this PDF:
Grounds on pins 9, 18 and 19 of C1. Use your DVOM or incandescent test light on these while the 5V reference is doing it's 5.81V thing. 100mV or less is what we want to see.
About the 5V reference circuit, there's a couple other quick tests we can do. Because it's an electronic throttle body, there's two 5V reference circuits at work. We know one is high, but knowing the health of the other would be valuable. From what I can tell, one 5V ref (coming from pin 29 of C2) feeds APP1, the crank sensor, the oil pressure sensor and the TPS. This is the one with 5.81V on it. The other (from pin 27 of C1) feeds the MAP, CMP, and APP2.
Probably the easiest place to measure both would be at the APP. It's the yellow/pink and the pink/yellow we're interested in.
Measure both with your DVOM and let us know what you find.
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No special DMM settings required for the grounds. Just connect the negative lead to battery negative, and make sure the meter reads B+ when you touch the positive lead on B+. Key on and backprobing during the checks of course.
If those check OK, then we can try disconnecting the other sensors on that 5V reference circuit. That'd be the throttle body and the CKP. If the 5.81V drops after disconnecting one or the other, then we're onto something.
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Jlr022581 wrote: And yes the oil gauge stop working at the same time the etc light came on and went into limp mode. It all happened at once. I went from no sensor light on to etc flashing and oil gauge stopped working and check gauge light and check engine light on all at once. It was crazy.
Good! :lol: That definitely makes me feel better about the replacement PCM.
While you're on the grounds, if you want to back up your DMM readings, you can also use a test light connected to B+. Should shine brightly.
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