****5V sensors question for the experts GMCODE P0641*****

[firefly9r68]

ok what i have in the shop is a 2004 GTO. i have replaced the Oil pressure sensor cause the oil warning keeps coming on, and the pressure is fine. then it is throwing the p0641. so after checking all the sensors they all read a little low. so i replace the computer still get the code. now i go and check the wires and they are all over the board. map is 9V OP is 7.8 AIR CON is 4.2 makes no scene. put the other computer back in and it doing the same thing.

ok so the car will act fine for the first few ins and then all of a sudden the oil pressure will go from 70 PSI to - readings. then just slowly count up and up and up. also another issue we are heaving is the coolant is always going off that its low.....LOL..there is more bugs in this car than i have ever seen.

so to try to fix this we have
checked all the volts at all the sensors, and tried to narrow it down to one of them
replaced the computer
banged head on wall.........

im out of ideas. and the grounds are all on too. and throwing no other codes


and the scans look good...so any ideas?

[Whiterhino]

Don't know if this will help... I ran into a similiar problem, but on my 06 1500hd. Everything was going nuts from sensors to the gauge clustor. I also have dual batteries in it. After tinkering a little bit on and off for a couple off days, chasing every ground, wire, unplugging harnesses. It ended up being a shorted battery. Even though it would start fine and register the correct voltage on the gauges. One off the batteries had a dead short/dead cells and was freaking out my whole setup. Threw in a new battery and all of the problems went away.

[angrygoat]

A short in the battery should show no voltage in the system. I would try unplugging all of the senors that you can and start plugging them back in one by one. I assume you have alldata or something of the like. It says they are all bussed together inside the ECM which Im assuming is why you replaced it. Seems like something is shorted to batt voltage affecting all of the sensors that rely of that 5v ref

[T-Bones Goat]

Steven, what did you get figured out on this? I went to the track last night and everything was fine. I warmed the car up and went to the staging lanes. I went to fire the car up and it went into safety mode. I didn't even get to make a pass. I'm now getting the P0641 and a P0690. Check out my oil pressure in the log file attached along with other readings. Keep in mind it was all I could do to keep the damn thing running in safe mode. Also, the oil pressure would read like 33psi with the key on and motor off.

[T-Bones Goat]

Another tidbit. I did a write entire for kicks and suddenly the oil pressure read correctly but I blew the fuse for the driver side coil packs. I replaced that and restarted the car and went back to reading crazy. I am going to try the battery just to see if that fixes the issue. I have a yellow top and the first one I had went out after only 6 months. The one that's in there now is only a month old.

[firefly9r68]

ours was a wiring issue.one of my mech just tapped into the wrong 5 volt wire. it was 5 volts but the one he used made the computer go haywire. we just bought a converter for it and fixed everything...ill have to think on yours..........

[Throttle]

i dont know if this helps but i have had five optima batteries in my car and they are junk nothing but problems from going dead in a day for no reason to just not working after sitting for a month,i put a cheap autozone battery in my car and problems went away

[T-Bones Goat]

ours was a wiring issue.one of my mech just tapped into the wrong 5 volt wire. it was 5 volts but the one he used made the computer go haywire. we just bought a converter for it and fixed everything...ill have to think on yours..........

I haven't tapped any 5v wires so that's not it for me. We did install an electric water pump so I will have to track the wiring for that.

i dont know if this helps but i have had five optima batteries in my car and they are junk nothing but problems from going dead in a day for no reason to just not working after sitting for a month,i put a cheap autozone battery in my car and problems went away

I am on number 3 myself. Swapping this one out will be my first step. If this POS is causing my problems, I will be one angry sob. On the other hand, an easy fix is always nice.

[T-Bones Goat]

Another tidbit. I did a write entire for kicks and suddenly the oil pressure read correctly but I blew the fuse for the driver side coil packs. I replaced that and restarted the car and went back to reading crazy. I am going to try the battery just to see if that fixes the issue. I have a yellow top and the first one I had went out after only 6 months. The one that's in there now is only a month old.

The battery is not the issue. A little more info. The fuse that I blew is the inj/ign fuse in the under hood fuse block. It is the first one of two in that block. Here is what is crazy about that fuse. When I pull it my oil pressure reads correctly. The only problem with that is the motor will not run without it. I got my mm out and checked voltage at that fuse. One leg reads like it should and has battery voltage. The problem is the other leg should read zero but it reads 4.92 volts. When I unplug the coil packs it goes up to 5.01. I am more confused now than I was before. HELP!!!

[wheelerman420]

Sounds as if your coil packs were using some of whatever voltage is bleeding thru to that circuit. from the looks of it there isnt really that much on that circuit. Do you have alldata or anything? Heres a few diagrams. Maybe they will help you out. Maybe a coil pack? Ign module? Lemme know if you need any other diags if you dont already have them.

[T-Bones Goat]

Sounds as if your coil packs were using some of whatever voltage is bleeding thru to that circuit. from the looks of it there isnt really that much on that circuit. Do you have alldata or anything? Heres a few diagrams. Maybe they will help you out. Maybe a coil pack? Ign module? Lemme know if you need any other diags if you dont already have them.

Thanks. I have a complete wiring diagram for the car and got some help from a friend with alldata. So far though I am still at a loss. I checked the voltage going to the oil pressure sensor and it is 10.58v. The high range is 5.02. Also the 4.92v at the fuse in question goes to zero v when I disconnect the harness from the ecm. I am leaning towards a bad ecm but want to make sure before I buy an expensive part. I still have to test the tank pressure sensor but that is about the extent of it. I'm running out of tests.