2009 Tahoe..P0641 code appearing ONLY when it rains - SOLVED

[Kervin]

I’ve got an 09 Tahoe LTZ 4x4 with 216,000 miles. This has happen a few times and I thought I had found this issue but I have not. Every time it rains I will get a P0641 code and the truck will go into limp mode and usually will stall out. Pretty hard to get it to crank back up and even if I do it keeps wanting to die intermittently as I drive. You can feel when something is shorting out as the truck will buck and want to die but it’ll stop and just drive in low power mode when it’s not shorting. Any help on where I can start. P0641 is the code that keeps appearing. Also when it’s shorting my engine oil pressure gage will go crazy.

 

[Geotrash]

I’ve got an 09 Tahoe LTZ 4x4 with 216,000 miles. This has happen a few times and I thought I had found this issue but I have not. Every time it rains I will get a P0641 code and the truck will go into limp mode and usually will stall out. Pretty hard to get it to crank back up and even if I do it keeps wanting to die intermittently as I drive. You can feel when something is shorting out as the truck will buck and want to die but it’ll stop and just drive in low power mode when it’s not shorting. Any help on where I can start. P0641 is the code that keeps appearing. Also when it’s shorting my engine oil pressure gage will go crazy.

My guess is that there's a short/fault in the wiring to the oil pressure sender. It requires a reference current supplied by the ECM that it may not be receiving all of the time. Check to make sure the connector is tight (a little hard to reach behind the intake) and check to make sure the wires aren't pinched cut between the sender and the harness.

 

[Kervin]

My guess is that there's a short/fault in the wiring to the oil pressure sender. It requires a reference current supplied by the ECM that it may not be receiving all of the time. Check to make sure the connector is tight (a little hard to reach behind the intake) and check to make sure the wires aren't pinched cut between the sender and the harness.

Alright I appreciate that. I’ll give that a shot tomorrow and see if I can see any out of the norm.

 

[wsteele]

Here is an interesting article on the code:

https://www.carparts.com/blog/p0641-code-sensor-reference-voltage-a-circuitopen/

 

[OR VietVet]

If you can get a flexible mirror with an extension, you can look back there and see what you want to lay your hand on when you check it. Any recent work on the rig? Since this only happens when it rains, I would check all ground connections for clean, tight and in tact, as well.

 

[Kervin]

Alright it’s been a min since I’ve fixed it but I wanna conclude this invade anyone ever had a similar problem. Before I go further thank y’all for the help. So I ended replacing every sensor in the 5volt reference circuit: oil pressure, a/c line sensor, map sensor, camshaft position sensor, and fuel tank pressure sensor. Nothing worked. I replaced my entire engine harness. Didn’t work. Swapped computers (ended up being a bad replacement) but found out my original computer was fine. I had brought it to a electrical shop before I replaced the harness as the problem was occurring and was told they couldn’t find it and they even sprayed the truck to try to get it to happen again and didn’t work. Was told by them that this problem is only possible in the engine harness and couldn’t be in the body control module or body harness. Wrong. I decided to spray every electrical connection underneath the truck and isolated it to a section of body harness under the drivers side inbetween the front door and the rear fender. Pulled my entire body harness out of the truck to where it runs down from the front wheel well to where I found a single nick in a blue wire that had corroded. This spot had a rubber section that went around the harness to protect it from the body mount for the cab to the frame. The rubber was on backwards where the opening was touching the mount allowing the wires to rub the cab mount and eventually led to the blue wire stripping and grounding out. I cut, spliced, soldered, and heat shrinked it back up and I’m good to go now. Zero issues.

 

[swathdiver]

Kervin, that code references a short to either the ECM or FPCM. You found the short and it seems like it was to the FPCM if I read your post right.

Access to the shop manual would have saved you a lot of time and money. AllDataDIY.

 

[Geotrash]

Alright it’s been a min since I’ve fixed it but I wanna conclude this invade anyone ever had a similar problem. Before I go further thank y’all for the help. So I ended replacing every sensor in the 5volt reference circuit: oil pressure, a/c line sensor, map sensor, camshaft position sensor, and fuel tank pressure sensor. Nothing worked. I replaced my entire engine harness. Didn’t work. Swapped computers (ended up being a bad replacement) but found out my original computer was fine. I had brought it to a electrical shop before I replaced the harness as the problem was occurring and was told they couldn’t find it and they even sprayed the truck to try to get it to happen again and didn’t work. Was told by them that this problem is only possible in the engine harness and couldn’t be in the body control module or body harness. Wrong. I decided to spray every electrical connection underneath the truck and isolated it to a section of body harness under the drivers side inbetween the front door and the rear fender. Pulled my entire body harness out of the truck to where it runs down from the front wheel well to where I found a single nick in a blue wire that had corroded. This spot had a rubber section that went around the harness to protect it from the body mount for the cab to the frame. The rubber was on backwards where the opening was touching the mount allowing the wires to rub the cab mount and eventually led to the blue wire stripping and grounding out. I cut, spliced, soldered, and heat shrinked it back up and I’m good to go now. Zero issues.

Thank you for following up!!

 

[89Suburban]

Alright it’s been a min since I’ve fixed it but I wanna conclude this invade anyone ever had a similar problem. Before I go further thank y’all for the help. So I ended replacing every sensor in the 5volt reference circuit: oil pressure, a/c line sensor, map sensor, camshaft position sensor, and fuel tank pressure sensor. Nothing worked. I replaced my entire engine harness. Didn’t work. Swapped computers (ended up being a bad replacement) but found out my original computer was fine. I had brought it to a electrical shop before I replaced the harness as the problem was occurring and was told they couldn’t find it and they even sprayed the truck to try to get it to happen again and didn’t work. Was told by them that this problem is only possible in the engine harness and couldn’t be in the body control module or body harness. Wrong. I decided to spray every electrical connection underneath the truck and isolated it to a section of body harness under the drivers side inbetween the front door and the rear fender. Pulled my entire body harness out of the truck to where it runs down from the front wheel well to where I found a single nick in a blue wire that had corroded. This spot had a rubber section that went around the harness to protect it from the body mount for the cab to the frame. The rubber was on backwards where the opening was touching the mount allowing the wires to rub the cab mount and eventually led to the blue wire stripping and grounding out. I cut, spliced, soldered, and heat shrinked it back up and I’m good to go now. Zero issues.

Holy crap good job dude thanks for letting us know.

 

[petethepug]

Nice work, good follow up AND follow through. Usually this level of diagnostic is from someone in the Armed Services or Airline tech.

I have one vehicle I handle like that I purchased in ‘90. It has a sticker on the fan shroud cover stating OBD EXEMPT