5v ref issue

[allisonw79]

I have 07 tahoe, it's giving a 5v ref. Backstory: engine oil pressure light kept coming on, replaces oil press sensor, it began making a knocking noise, I replaced engine w crate motor. At times when I would crank it, the starter would spin...turn it off then bake on and it cranks. After engine replacement, it kept doing it so I had starter replaced. I also replaced fuel pump in the event that was causing starter to spin over. Lastly, the stabiltrak light came on., reduced power engine, gas pedal not working. I've checked all wires and replaced cam shaft, crankshaft, ac high pressure, fuel pressure sensor. Still getting 5v ref issue. Crazy thing is I have no rpms when camshaft sensor is plugged in, if I unplug it I have rpms. Pls help.

 

[Fless]

Welcome to TYF from Colorado!

When you say it's giving a 5v ref., where is that measured, on what circuit? Lots of the components and sensors use a 5v reference voltage.

 

[allisonw79]

Welcome to TYF from Colorado!

When you say it's giving a 5v ref., where is that measured, on what circuit? Lots of the components and sensors use a 5v reference voltage.

Well that's the thing...we have a code reader, the sensors as we read each one says (ac high pressure)
5v 1 5.5,
5v 2 5.5
Sensor reading is around 0.231 or 0.265
The code that keeps coming up is p0641 and p0651

 

[allisonw79]

Well that's the thing...we have a code reader, the sensors as we read each one says (ac high pressure)
5v 1 5.5,
5v 2 5.5
Sensor reading is around 0.231 or 0.265
The code that keeps coming up is p0641 and p0651

We are tracking all those sensors
Camshaft
Crankshaft
Fuel pressure
Oil pressure
MAF
MAP
AC High pressure
Accelerate pedal

 

[j91z28d1]

this is a curious one I've not heard of? seems your 5v output from the ecm is a half volt to high? interesting. I'll attach what I found. I read it as unhook every sensor on line 1 and 2 then test the 5v at the sensor plugs and see if it's still wrong. at that point I'd personally unpin that pin at the ecm and test it there before replacing the ecm. it's so rare that a ecm actually fails and 2 outputs at a time would seem to be more rare.

but good luck. sounds like a lot of digging around under the hood wiring. a shop will probably throw an ecm at it first because that's the least labor for them and most money out of you.

 

[mikez71]

Am I reading it right, that the starter will self crank after turning off the motor?

That does seem odd that there are no RPMs with the cam sensor disconnected. Definately check the wiring to cam sensor! (sounds like you may have already)

Also, looking at J91z28d1's attachment, it seems like accelerator pedal position can set both of those codes, whereas the other sensors will only set one code.. AC Pressure supposed to be Accelerator position in your scanner? idk

 

[allisonw79]

Out of curiosity when I'm reading the code reader on any given sensor, I check the box for 5v1 and 5v2 and then the specific sensor....the reading displayed should be:
5v1 5v or near that amt
5v2 5v or near that amt
Sensor should be what?
We disagree on the readout for this line item...I say that 0.265 or whatever is OK for the truck being off, my husband says it shld say 5v also.

 

[mikez71]

5V ref should be 5V. Sensor signal would be a different wire that could be anything (less than 5V ref)

 

[j91z28d1]

yes, the sensor voltage is going to be less than 5v. that the output the ecm turns into a useful number. it will vary depending on the kinda of sensor thou. like say cam and crank should put out a sign wave of some sort, usually a square wave and the frequency is counted by the ecm.

for the starter I'm taking it you mean the starter electric motor would spin but did not engage the flywheel to turn the engine over. that isn't the most common way they fail, but most likely not part if this issue.


the 5v reference code sounds to me like it's being set because it's reading to high from the ecm, not about what reading is coming back from the sensor. the first thing I would do was test the 5v at the sensor plug under the hood with a volt meter and see if it matches your scanner.

for the rpm not working on when you plug in the cam sensor. is that scanner rpm or dash tach? I hate to just throw parts at it. but that sensor might be bad. I'm not sure of a eazy way to test it without a way to back prob the sensor plug and know what you're looking for.

 

[Joseph Garcia]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

You are already receiving clarifying questions from the knowledgeable folks on this Forum.