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Jerry Newton
Jerry Newton, Chevy Technician
Category: Chevy
Satisfied Customers: 4412
Experience:  ASE Master Technician, L1, Master GM Technician. Over 20 years of bumper to bumper GM experience.
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I have a Hummer 2004 H2 and I am getting P0641 code and my

Customer Question

I have a Hummer 2004 H2 and I am getting P0641 code and my oilpressure gauge is reading higher than it should. At first, my truck would start and barely stay running, and it was throwing codes for Mass Air Flow out of range. Then after a few battery disconnecting attempts and restarts, now it is throwing the P0641 and the previously mentioned oil pressure thing. Is my ECU shot?
Submitted: 8 months ago.
Category: Chevy
Expert:  Jerry Newton replied 8 months ago.
Remove the connector for the oil pressure sender, turn the key on, and see if you have 5v at the gray wire.
Customer: replied 8 months ago.
I dont have 5v on the gray, but i have 5v on the yellow/tan wire to the left of it on the plug.
Expert:  Jerry Newton replied 8 months ago.
Go to the MAP sensor and see if you have 5V on the gray wire at that connector.
Customer: replied 8 months ago.
On the plug fore the Mass Airflow Sensor, I have as follows: 5v on each of the yellow wires, 12v on the pink wire, and nothing on the black and grey wires.
Expert:  Jerry Newton replied 8 months ago.
I need you to look at the MAP sensor connector, not the MAF. Do you know where it's located?
Customer: replied 8 months ago.
No, please advise.
Expert:  Jerry Newton replied 8 months ago.
It's on top of the intake manifold, toward the rear of the engine. If you remove the plastic engine cover, it's readily accessible right on top.
Customer: replied 8 months ago.
What i have on the top of the intake manifold, at the back of the engine are two plugs. One has two wire, one light blue and one dark blue. The other plug has a yellow, green, and orange wire. Which one is it?
Customer: replied 8 months ago.
The three wire plug is centered on the back of the manifold, and the two wire plug is mounted off to the driver side. The only other plug on the top of the manifold is a two wire plug at the FRONT of the manifold adjacent a hose with a green valve cap on it.
Expert:  Jerry Newton replied 8 months ago.
MAP is going to be orange/black, light green, and gray wires, 3 wire connector. I'll attach a drawing that shows the location. It's #1 in the upper left drawing in the attachment.
Customer: replied 8 months ago.
Got it, stand by...
Customer: replied 8 months ago.
I have 5v on the yellow, nothing on the grey wire in the center of the plug, and nothing on the orange.
Expert:  Jerry Newton replied 8 months ago.
5 volts should be on the gray wire, and the gray wire should be in pin C. This is not right. Disconnect the oil pressure sensor and check that voltage on the gray wire again.
Customer: replied 8 months ago.
The only place I am getting 5v at the oil pressure sensor plug is on the yellow wire to the left of the grey wire when looking at the plug with the two wires at the top and the single wire at the bottom.
Expert:  Jerry Newton replied 8 months ago.
5 volts should be at pin 2, see diagram. You don't have 5v on this gray wire at either the MAP or oil pressure sensor? But you have 5v on the light green wire at the MAP and 5v on the tan/white wire of the oil pressure sensor? Tan/white wire is in pin 3, per the drawing.
Customer: replied 8 months ago.
MAP Sensor: 5v on the yellow (or it may be tan) wire, which is the wire on the far right when looking at the plug with the securing clip on the top.Oil Pressure Plug: 5v on the yellow (or it may be tan). There is no voltage on the tan wire with the white stripe.
Expert:  Jerry Newton replied 8 months ago.
OK. There is obviously an issue with the 5v reference circuit. It's split into two on this engine, that's why we're only looking at the MAP and oil pressure sensors, those are the only two sensors that use this particular 5v reference. That wire is broken somewhere between the PCM and those sensors, or it's touching ground somewhere in that span, or the PCM is no good. Before you replace the PCM, make sure it's not just a wiring issue, I'd put a voltmeter on that grey wire and just start wiggling the harness anywhere I could to see if it makes that 5v come back to life. You can check this 5v circuit right near the PCM, too, it goes into pin 7 and 48 of the blue connector. Though these are the same circuit, the oil pressure sensor and the MAP both have their own pin for it on the PCM, the circuits are connected together within the PCM, so if the gray wire is grounded for the oil pressure sensor, it will kill the 5v reference to the MAP as well, and vice versa.

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