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I've got a '03 cadillac dts 4.6L northstar in here and i…

Hey man, I've got a...
Hey man, I've got a '03 cadillac dts 4.6L northstar in here and i have a fuel level sensor code. Voltage too high. i know via wiring diagram that the purple wire is the signal wire from the sending unit to the pcm. However, i have 5 volts on said signal wire. i went straight to the pcm and cut the signal wire just before the pcm C2 connector and i still have 5 volts {reference voltage} coming out of the pcm. with the exception of the pcm being internally shorted im out of ideas.
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Answered in 1 minute by:
10/18/2017
Amedee
Amedee, Cadillac Technician
Category: Cadillac
Satisfied Customers: 27,289
Experience: ASE certified Technician advanced level specialist. Wisconsin certified emissions state inspector
Verified

Hello and welcome!

My name is ***** ***** I can assist you with your question.

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Are you saying you have 5 volts on this purple wire leaving the PCM after you cut this wire?

May I get the code you have stored in the computer?

Thank you

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Customer reply replied 4 months ago
5 volts after out of the pcm after cutting the wire.
Customer reply replied 4 months ago
p0463

Thank you.

One minute please

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Thank you for your patients.

The 5 volts coming out of the PCM is normal. This is OK. This is how the system works.

However, the sending unit should pull this voltage down depending on the fuel level in the tank.

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Customer reply replied 4 months ago
the variable resistor in the tank should pull down voltage to an acceptable value?
Customer reply replied 4 months ago
of course corresponding to the fuel level. more fuel is higher voltage?

YES sir thats correct.

I would plug everything back in, hook everything back up and recheck the voltage on this purple wire. It should move or change as the float level is changed.

The manufacturer only provides the resistance specs. If you want to ohm out the sending unit, the specification is 250 ohms when full and 40 ohms when the tank is empty.

Of course, be sure the black wire has a good ground.

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Customer reply replied 4 months ago
but i thought the voltage should cap out at 3.5 volts i dont understand what i should see on the signal wire then.

Just be sure it varies when the float goes up and down.

With the connector plugged into the sender, be sure the voltage on the purple wire is NOT 5 volts. If so, there is a problem. When the resistance goes up (when the tank is full) the voltage will be low.. because of more resistance.

When the resistance is low, the voltage will be higher.

Does that make sense?

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Customer reply replied 4 months ago
i get it that the resistance should change but i'm failing to convert that to voltage change. and it is 5 volts with everything connected
Customer reply replied 4 months ago
that's what started me on the path to the pcm.
Customer reply replied 4 months ago
how do i stop this site from sending me text messages every time you reply?

Got it!

I would check the resistance specs of the sending unit next.

Also, check the ground on the black wire. It could be a faulty ground preventing the voltage from being pulled down with everything connected. That would explain the 5 volts on the purple wire.

I am sorry, I don't know anything about text messages sent from the site.

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Amedee
Amedee, Cadillac Technician
Category: Cadillac
Satisfied Customers: 27,289
Experience: ASE certified Technician advanced level specialist. Wisconsin certified emissions state inspector
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Satisfied Customers: 27,289
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