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GM Tech (Cam)
GM Tech (Cam), Chevy Technician
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Experience:  GM Grand Master Technician 2007. 14 years experience.
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Chevrolet Tahoe LT Dave, I sent my tahoe to dealer to check

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I sent my tahoe to dealer to check all sensors that were addressed and they didn't find anything wrong. They couldn't not checked the oil pressure sensor at motor compartment...

Saturday i was running the motor and i was able to look the console and saw Oil pressure being dropped to cero and then suddenly goes up, as normally reads. On that instant, failure appear again....

It could be a security system when oil pressure drops dangerously issued by computer to demand an engine check?

Is so, problem must be located at this sensor, cable, connector or other related electrical or electronic component.

What do you think? There is a way to check this sensor (i mean conductivity test or other)

Thank you

GM Tech (Cam) :

Hello, I'm Cam. Please include all the details about your issue so I can accurately advise you. I cannot see your vehicle so please be detailed.

GM Tech (Cam) :

I see Dave is offline, can I assist you?

JACUSTOMER-nykpfw43- :

An ENGINE POWER IS REDUCED message, an illuminated Check Engine lamp and DTC P0641 may be set on some 2006-2010 Tahoe models. These conditions may be intermittent. Other DTCs that may set include: P0532, P0522, P0452, P0335, P0106, P0101 and P0068

JACUSTOMER-nykpfw43- :


P0641 CHEVROLET - 5 Volt Reference Voltage Incorrect



- Engine Light ON (or Service Engine Soon Warning Light)


Possible causes

- ECM Short circuit condition
- Shorted sensor on 5 volt circuit
- Failed ECM


P0641 CHEVROLET Description


The Service Manual says The Engine Control Module (ECM) detects a voltage out of tolerance condition on the 5V reference 1 or 2 bus for more than 0.5 seconds.


When is the code detected?


The ECM has detected the sensor 5 volt reference circuit voltage is higher or lower than expected



JACUSTOMER-nykpfw43- :

Dave's response:...

JACUSTOMER-nykpfw43- :

The 5-volt reference 1 bus provides 5 volts to the following sensors:

  • The manifold absolute pressure (MAP) sensor

  • The fuel tank pressure (FTP) sensor

  • The air conditioning (A/C) refrigerant pressure sensor

  • The accelerator pedal position (APP) sensor 2

  • The engine oil pressure (EOP) sensor

  • The camshaft position (CMP) sensor

You will need to check the wiring at each of these sensors for a short to ground or a possible short to power. A scan tool that shows live data would also be helpful. That way you can monitor the voltage readings from these sensors when the problem occurs and then unplug the sensors one at a time to determine if you have a shorted sensor.

JACUSTOMER-nykpfw43- :

Waiting on your comments...

GM Tech (Cam) :

Ok, I would like to start fresh for now, do you get a warning when the pressure drops to 0? And were there codes that you got?

JACUSTOMER-nykpfw43- :

The code is P0641. The failure is like you disconect several cylinders at a time, gearbox start to shift very rude and you can't speed up more than few km/hr. Low engine power is issued and failure remains until you erase the code with a scanner or turn off the vehicle and wait more than 15 minutes...

JACUSTOMER-nykpfw43- :

its appereance is random, so nothing to do with something that heats on, etc...

GM Tech (Cam) :

Ok, there is another bulletin you can check, it suggests there may be a clearance issue between the front drive shaft and the wiring. Look at that and reply back here to me.

JACUSTOMER-nykpfw43- :

this is the real problem. Maybe the malfuction is sudden and appear short in time but failure is holded ON by car computer, issuing a yelow engine light on and multiple several failures messages like transmission failure, motor is on reduce power, etc... until you erase it or turn off the car.

GM Tech (Cam) :

This wiring would account for those issues as the data line to the back goes past there.

JACUSTOMER-nykpfw43- :

were is the bulletin? were is located that front drive shaft, do you have pictures to show me?

GM Tech (Cam) :
#PIP3809C: SES Light - Inspect wire Harness For Short On Front Drive Shaft - (Feb 12, 2009)


Subject:SES Light - Inspect Wire Harness for Short on Front Drive Shaft


Models:2007-2009 Chevrolet Avalanche, Silverado, Suburban, Tahoe

2007-2009 Cadillac Escalade

2007-2009 GMC Sierra, Yukon

Most Recent Body Style withXXXXXand V8 Engine

This PI was superseded to update model years and DTCs. Please discard PIP3809B.

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.


Some customers may complain of an intermittent crank no start, no crank, SES light, and/or security light. Upon inspection, the technician may find low fuel pressure and/or any of the following DTCs: P0030, P0036, P0050, P0053, P0054, P0056, P0059, P0060, P069E, P0102, P0113, P0118, P0131, P0132, P0135, P0137, P0140, P0141, P0161, P0230, P0335, P0341, P0151, P0152, P0155, P0157, P0158, P0161, P0171, P0172, P0174, P0175, P0449, P0452, P0532, P0641, P069E, P1133, P1153, P1682, P2101, P2534, and/or P2544.


If the SI diagnostics do not isolate a cause for this concern, inspect the wiring harness above the front drive shaft for a potential short to ground, near the transfer case side of the front drive shaft as shown below. Repair any chaffed wires by following SI repair procedures.

The harness should be secured to a supporting bracket with a plastic clinch style clip. If the harness has contacted the front drive shaft because of a missing retaining clip, secure the harness to the metal fuel line bracket with a tie strap to prevent a reoccurrence. If the retaining clip is present but contact still occurred, relocate the inboard clip (part of the wiring harness) and tie strap the harness to prevent a reoccurrence.

Here is an example of a harness that is too close:

GM Tech (Cam) :

Full Size Image

JACUSTOMER-nykpfw43- :

ok, let me look at it. I'll be right back...

GM Tech (Cam) :


JACUSTOMER-nykpfw43- :

I check the motor vault and din't see anything wrong or cable near the drive shaft. In fact, the photo doesn't match my vehicle...

JACUSTOMER-nykpfw43- :

it is located inside the driver cabin?

GM Tech (Cam) :

No, under it behind the transmission,

JACUSTOMER-nykpfw43- :

do you mean at motor compartment or below the car?

JACUSTOMER-nykpfw43- :

my knowledges are limited with car's nomenclature

GM Tech (Cam) :

Below. the transfer case is bolted behind the transmission and the transmission behind the engine. So this area is under the vehicle somewhere at the back of the drivers seat , but under the vehicle.

JACUSTOMER-nykpfw43- :

Ok. I have to re-check it...

JACUSTOMER-nykpfw43- :

How much time do i have to do that check?

JACUSTOMER-nykpfw43- :

I need at least half hour...

GM Tech (Cam) :

Take your time, I need to go offline for an hour or so, and I can look for your reply back here then.

JACUSTOMER-nykpfw43- :

Ok.. Thank you...

JACUSTOMER-nykpfw43- :

if you have a Email, to answer you it will be awsome...

GM Tech (Cam) : I cannot see your email, nor can I give mine out, but just reply to this thread to pick up later on this issue.
JACUSTOMER-nykpfw43- :

I just checked and my Tahoe is 4X2, so that shaft doesn't exist. there're plenty of space and no cables looked damaged or broken.

GM Tech (Cam) :

Ok, then we need to test the wiring for the fuel pressure sensor to the fuel pump control module.

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