Code P0641?

Tiny
DILLON SHUEY
  • MEMBER
  • 2007 PONTIAC G5
  • 2.2L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 122,000 MILES
The fuel pump burnt out on my car. I replaced the fuel pump with one off of Amazon. It ran fine. The connector that connected to pump was burnt but still worked. I recently bought a whole pigtail bundle from a scrap yard. I came home, dropped the tank and put the new harness in. Now all it does is crank but won't start. I tried putting the old harness back in. Still nothing. I disconnect the map sensor and it starts and runs (reduced engine power, of course) I plug the map back in and it shuts off the engine! I've replaced the MAP sensor and the CPS! Any ideas?
Tuesday, February 21st, 2023 AT 4:21 PM

1 Reply

Tiny
AL514
  • MECHANIC
  • 5,068 POSTS
Hello, so this is a pretty strange issue, but the main issue for the code p0641 is the 5vRef number 1, and there are other 5vRef circuits on this vehicle. But the MAP uses 5vRef 1 and so does the Fuel Tank Pressure sensor. And what I found is that the ECM uses the MAP for special fuel injector timing/pulse width. I'll post all this info. So, the question is why did the fuel pump harness burn up for one, and two what is happening to the 5vRef for the MAP sensor when you plug the map back in? Is it dropping off to 0volts or is the 5 volts missing altogether at the map sensor. So, unplug the MAP, turn the key to on engine off and check the 3 wires of the MAP sensor for a 5volt feed.
The grey wire on the MAP should be the 5Vreference feed.

I think you're going to find the 5volt reference circuit missing, and there might be a burned-out sensor somewhere that is shorting the 5volts out to ground. So possibly the Fuel tank pressure sensor. The P0641 is for that 5volt is missing or open circuit or is shorting to Ground and that's pulling it to 0 volts.
Definitely a weird issue though. I'm surprised it didn't set anymore codes. Hopefully the ECM didn't get damaged.

https://www.2carpros.com/articles/how-to-use-a-voltmeter
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Wednesday, February 22nd, 2023 AT 12:04 PM

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