P0641-Engine power is reduced

[SAtownCAMARO]

Been getting this code for awhile now almost on a daily basis and just looking for any additional advice. I'm aware that it's a 5-volt ref fault and so far I have done the following as part of the trouble shooting:

1.) replaced accelerator pedal
2.) tried out a different throttle body
3.) had the car retuned (Dyno)- was previously only street tuned
4.) replaced MAP sensor
5.) replaced MAF sensor
6.) overlooked majority of the wire harness connections accessible from the engine bay looking for a possible softset

Couple of things to note and things I have noticed:

1.) about 2 weeks prior to this happening my oil pump went out and had to be replaced. Maybe related?
2.) seems to happen more often once the car is hot/warmed up. I drive 11 miles to work and it usually happens once I exit the freeway and usually if I have to stop and shift up through the gears again.
3.) usually happens in between shifting gears but not 100% of the time.
4.) if I turn on the AC, this will ALMOST trip the code everytime. Again, not 100% of the time but most. I hardly ever use my AC, only if on a phone call.
5.) seems like my TPMS warning light comes on for my left front tire about 30 seconds after it goes into limp mode....weird. Again not everytime but enough to get my attention.
6.) when in limp mode, about 50% of the time my oil pressure gauge starts going bonkers. If I'm sitting still, the needle bounces around almost all the way to 0 then back to around 70. Even if on the highway, sometimes if I take my foot off of the gas pedal, the needle bounces around crazy.
7.) about once a month, things get really weird and as I'm driving it will start studdering really bad. I will be giving it steady pedal but it drives like I'm bouncing my foot on and off the pedal. The first time it did this I turned it off and the car wouldn't start for 10-15 minutes. Then it went away.

I'm pretty sure the car is out of the warranty and besides, I will be putting a supercharger on it in about 1-2 weeks. My friend is going to help me during the install and see if we can find a pinched/damaged wire anywhere but any other advice would be greatly appreciated. The car is a 2010 M6 SS. Car has around 40k miles and has your usual bolt-ons: intake, exhaust, headers, cam, etc.

Thank you,

[TommyTheCat]

That's the only code you're getting? Overlooking the wire harness won't do much unless there's an obvious problem, better to pin check the harness which is very time consuming.
Also is that an L99 or LS6?

And I don't think there was any point in trying the MAF sensor, it shouldn't even be in the same circuit. This might help:

• The 5 V reference 1 circuit provides 5 V to the following sensors:
  • Manifold absolute pressure (MAP) sensor
  • Fuel tank pressure sensor
  • Accelerator pedal position (APP) sensor 2
  • Engine oil pressure sensor
  • Air conditioning (A/C) refrigerant pressure sensor
  • Camshaft position sensor

To check these sometimes it's possible to simply disconnect the sensors and see if the problem goes away one at a time, but that's not always true, and you have to do that while the problem is occurring.

Since you said the air conditioner causes the problem, you might have a problem with the pressure sensor or the harness going to it.


It's always possible your PCM is bad, too. Which in CANBUS cars can cause other electrical problems like the tire pressure light coming on... Have you checked the tire pressure manually and electronically? On the left turn signal you can press menu and scroll to the tire pressure. You shouldn't have a problem with the wrong readings since most Camaros cannot have tires rotated.

And have you actually checked the voltage when the light is on? It's supposed to only trigger above 6 volts

*EDIT*
Don't forget to check the basics first! Check all fuses and relays... Can't tell you how many times I've started working on a car that was supposedly checked for bad fuses and two hours later after scratching my head I double check the fuses and find one that's blown. And check when it's having the problem.


This probably won't help but... eh:
TSB 07-06-04-019D (Shows a different P code but with the same description)

[SAtownCAMARO]

Thanks for the advice and your time to type up that response. I'll definitely do some of the items you listed below.

I did find an exposed wire right at the Wire Harness connection for the AC pressure sensor so I temporarily taped it up but it did not eliminate the problem.

I also checked my Tire electronically like you said and it was showing low tire pressure at 27PSI but the warning light had not come on. Like I said before, the warning light will usually come on once the car has gone into limp mode. I will manually check the tire later on today once I get out of work.

The car is an LS3.

Thanks again for the advice. I'll have to do some research on finding out exactly where the Fuel pressure sensor and the crank position sensor are.

[TommyTheCat]

The fuel pressure sensor for the V8 camaros are on top of the gas tank... good luck lol
You'll have to drop the exhaust and differential. I can send you a diagram of the fuel tank and show you which sensor it is exactly

The camshaft sensor is real easy to get to I can send a diagram of that too

PM me and I can send them.

[FelipeShaw]

Did you figure it out. Mine is doing the exact same thing?

[Ryguy1188]

Is there any update to this? I am having the same issue.

[Blu Ray]

Any updates -- A friend car is throwing the same code with the same issues

[bhopp@matixcomputer.com]

Anybody figure this out. I was chatting in a parking lot yesterday and mentioned that my car goes into the "Reduced Engine Power Mode", some girl overheard me and stopped and said she got so disgusted that she finally traded her camaro in for another car (non GM). This is very frustrating for me being a computer programmer we rely on google to find solutions (and almost always do), but this problem just does not seem to have a solution.

[MrChrisLS3]

Originally Posted by TommyTheCat

That's the only code you're getting? Overlooking the wire harness won't do much unless there's an obvious problem, better to pin check the harness which is very time consuming.
Also is that an L99 or LS6?

And I don't think there was any point in trying the MAF sensor, it shouldn't even be in the same circuit. This might help:

• The 5 V reference 1 circuit provides 5 V to the following sensors:
  • Manifold absolute pressure (MAP) sensor
  • Fuel tank pressure sensor
  • Accelerator pedal position (APP) sensor 2
  • Engine oil pressure sensor
  • Air conditioning (A/C) refrigerant pressure sensor
  • Camshaft position sensor

To check these sometimes it's possible to simply disconnect the sensors and see if the problem goes away one at a time, but that's not always true, and you have to do that while the problem is occurring.

Since you said the air conditioner causes the problem, you might have a problem with the pressure sensor or the harness going to it.


It's always possible your PCM is bad, too. Which in CANBUS cars can cause other electrical problems like the tire pressure light coming on... Have you checked the tire pressure manually and electronically? On the left turn signal you can press menu and scroll to the tire pressure. You shouldn't have a problem with the wrong readings since most Camaros cannot have tires rotated.

And have you actually checked the voltage when the light is on? It's supposed to only trigger above 6 volts

*EDIT*
Don't forget to check the basics first! Check all fuses and relays... Can't tell you how many times I've started working on a car that was supposedly checked for bad fuses and two hours later after scratching my head I double check the fuses and find one that's blown. And check when it's having the problem.


This probably won't help but... eh:
TSB 07-06-04-019D (Shows a different P code but with the same description)

That's kinda funny, I read the post and read about the oil pump being replaced, then started thinking that there could be an issue with a ground. Oil pressure sending unit, Camshaft position sensor were my first thought on the faulty ground. Throw in that the A/C and the pedal sensor are on the same circuit, well there ya go.

[BandRcAMARO]

Anything on how you got this issues fixed?