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Old 08-12-2017, 04:56 PM   #1
ScarTissue48
 
Drives: 2010 SS
Join Date: Mar 2013
Location: Arkansaw
Posts: 48
p0641

Ok, so I'm having trouble with a p0641 code that is also throwing codes for each sensor on that 5v reference circuit.

I did a cam swap about a year ago and haven't driven the car just a whole lot, but have put several thousand miles on it and have done an oil change. BTR stage 4, putting down about 472 RWHP. After getting tuned, it's ran like a dream with no problems.

But the other day, coming back home from a trip to town, I happened upon a motorcycle that wanted to go fast, so I did a little high rpm driving and shifting to keep up with him, just normal hard driving. I got to my turn off and let off maybe a couple hundred yards ahead of it, and coasted into it, and maybe 50 feet off the main road I kicked into Engine Power Reduced(limp mode). Gauges all looked fine, just a CEL, Service Stabilitrack, and limp mode. Car ran and idled fine, just really limited acceleration....could still get up to speed it just took forever.

Made it back to the house just fine, gauges still fine. Hooked up the HP Tuners and checked the codes, and it's p0641 along with several other codes for sensors on that 5v reference circuit. So after clearing and checking again several times, and starting the car a couple times also to clear and re check, over a day or 2, now the oil pressure gauge shows 0, while the car still starts and runs fine. I believe I still have oil pressure, i just think that 5v reference is making all those sensors read weird or not at all.

So it's sat there a bit as I've stewed and I finally tore into it and checked all the fuses and relays, replaced the battery that had been on the decline for a while, and located and unplugged each sensor and inspected while I was there. Each time I would go and check the codes again, and the p0641 is constant with it seems random combos of other codes for those 5 sensors on that 5v reference. I read somewhere that if you unplug the problem sensor, if that's the issue, and clear the codes it may keep the p0641 code from throwing, but that didn't work, and as of right now I've got all 5 sensors unplugged and that p0641 is still throwing.

Current state of the car:

A/C Refrigerant Pressure Sensor unplugged
Manifold Absolute Pressure/BARO Sensor unplugged
Fuel Pressure Sensor unplugged
Cam Position Sensor unplugged
Oil Pressure sensor unplugged
Coil packs unplugged and pulled
Intake and all of it's plugs unplugged and pulled

So with all of that unplugged and the intake off, here is my current batch of codes:

0x7E8: P0107 - Manifold Absolute Pressure/BARO Sensor Low (Pending, Current, Permanent)
0x7E8: P0122 - Throttle/Pedal Position Sensor A Circuit Low (Pending, Current, Old)
0x7E8: P0223 - Throttle/Pedal Position Sensor/Switch B Circuit High (Pending, Current, Old)
0x7E8: P0443 - Evaporative Emission System Purge Control Valve Circuit (Pending, Current)
0x7E8: P0452 - Evaporative Emission System Pressure Sensor/Switch Low (Permanent)
0x7E8: P0532 - A/C Refrigerant Pressure Sensor A Circuit Low (Current, Old, History)
0x7E8: P0641 - Sensor Reference Voltage A Circuit/Open (Permanent)
0x7E8: P069E - Fuel Pump Control Module Requested MIL Illumination (SES, Pending, Current, History)
0x7E8: P1682 (Permanent)
0x7EB: P018C - Fuel Pressure Sensor B Circuit Low (Pending, Current)

I also went through and checked grounds on both heads, all seem stable and tight, wires look fine.


So I'm kind of stuck on what to do next. I have a digital voltmeter and checked voltage on each sensor. I did this by just sticking the positive end of the voltmeter into the holes on the sensors, and the majority of them read very low voltage, while i believe 2 of what I assume to be the 5v reference holes read right around 5v or a little less...4.8 range. I have never used a voltmeter before and have next to no idea what I'm doing outside of a few youtube vids.

Only other thing of note is when I checked the cam position sensor, it was dirty from a pre-cam oil leak I had that I was able to fix during the cam swap--front main seal. It was also jammed right up against the ac line bracket that bolts to the front of the oil pan, which was not bolted back to the pan after the cam swap. After getting that readjusted and unplugging the sensor, on inspection I noticed some wire showing on the 5v reference wire on the cam position sensor plug. It looks like it could have definitely been touching that metal AC bracket, and I assumed that was my problem. However, that is one of the few 5v reference wire holes that read 4.8v, and after moving the ac bracket and making sure no contact is being made, there is no change in my DTCs, same as before. So i think that wire showing isnt causing any problems, but do plan to rewrap it and clean it up before reinstalling.

So......
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I guess I'm just looking for any insight or guesses as to what caused/is my problem, and what my next steps should be. At this point I'm wondering if the PCM may have shorted out when the cam position 5v wire touched that metal AC bracket. Other than that I have no idea outside of some minor thing that I just haven't found. Thanks for any feedback!
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Old 08-14-2017, 11:52 AM   #2
ScarTissue48
 
Drives: 2010 SS
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Looks like I may have posted this on the wrong board... Can a mod move this over to the Issues/Problems board?
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Old 08-16-2017, 06:43 PM   #3
ScarTissue48
 
Drives: 2010 SS
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Ok so with all the sensors unplugged, the 5V reference wires are reading 4.8 for the map and camshaft position sensor, but the rest I can only get a reading of 0.1 to 0.12 volts. Sound like a shot pcm?
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Old 09-25-2017, 04:00 PM   #4
TheInfamouSS
 
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Drives: 2014 Chevy Camaro 2SS 1LE
Join Date: Jan 2017
Location: North Jersey
Posts: 87
What ever happened? I am having this same issue with my car now
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Old 10-19-2017, 03:42 PM   #5
ScarTissue48
 
Drives: 2010 SS
Join Date: Mar 2013
Location: Arkansaw
Posts: 48
I decided to swap out the pcm, so went ahead and put the car back together. Went ahead and tried to start it and see how it did before ordering the pcm, and the dang thing ran fine, no check engine lights. I think it was either a ground that I had taken off and reinstalled to reroute the wiring harness, or a 5v reference wire on the cam position sensor I taped up. I did a read entire with hptuners to read the tune, so that may have reset something and fixed whatever the issue was. I really have no idea, but my radio display did quit working right when the car went to running fine again, and the fuse for that is fine, so Im kind of at a loss right now as to what is causing that and if it's related to my 5v problem. Surely not but it makes me wonder!
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