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post #1 of (permalink) Old 10-01-2019 Thread Starter
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fellow 2000 - 2005 Impalas, can you do me a favor

Hello 2000 - 2005 Impala owners, on the key ignition switch, there is Off, Accessory, On, Start positions,

1. Can you tell me, if you turn your key from Off position to Accessory position, does it turn on the fuel pump?

2. And then from On position to Accessory position, does it turn on the fuel pump?

I thought only when the key is turn to the On position is when the fuel pump turns on.
But my ignition switch seems to be turning on the fuel pump from the Off position to Accessory position and On position to Accessory position. So in short, seems the Accessory position is turning on the fuel pump also.

Thank You
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post #2 of (permalink) Old 10-01-2019
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'05 ls with 3.8
The fuel pump primes from off to accessory, accessory to on and from on to accessory. My pump seems to be functioning the same as yours. Does seem strange it would prime in accessory.
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post #3 of (permalink) Old 10-02-2019 Thread Starter
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Originally Posted by Bill58 View Post
'05 ls with 3.8
The fuel pump primes from off to accessory, accessory to on and from on to accessory. My pump seems to be functioning the same as yours. Does seem strange it would prime in accessory.
Thanks Bill58, yes it does seem strange the accessory position would prime the fuel pump. Other automotive makes i have know to only prime the fuel pump from the ON position. I have an 05 3.4 that is a having a CRANK NO START issue. I thought this would have been the cause of no start.
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post #4 of (permalink) Old 10-02-2019
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Quote:
Originally Posted by Nacho View Post
Thanks Bill58, yes it does seem strange the accessory position would prime the fuel pump. Other automotive makes i have know to only prime the fuel pump from the ON position. I have an 05 3.4 that is a having a CRANK NO START issue. I thought this would have been the cause of no start.
Do you have fuel pressure (key on engine off should be 52-59 psi)?
Do you have spark?
Will it start using starting fluid?
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post #5 of (permalink) Old 10-02-2019
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Originally Posted by Nacho View Post
Thanks Bill58, yes it does seem strange the accessory position would prime the fuel pump. Other automotive makes i have know to only prime the fuel pump from the ON position. I have an 05 3.4 that is a having a CRANK NO START issue. I thought this would have been the cause of no start.
I too think it's kind of weird to send power to the fuel pump on ACC.

Starting at the pump, the PCM controls it via the fuel pump relay.

Looking farther upstream, using the drawings I have access to, I can't find one focused on the ignition switch, but, from what I pieced together, it works as follows:

START and ON both send +12V to the pink wire which goes to both the PCM and BCM.

START and ON also both send +12V to the dark green wire which also goes to both the PCM and BCM.

START also sends +12V to the yellow wire which goes to the PCM.

ACC and ON both send +12V to the brown wire, which goes to the BCM.

(Keep in mind, these connections are sending signals as much as they are sending power.)

START and ON go to the PCM via 3 different wires, but ACC only goes to the BCM. So, for ACC to cause the fuel pump to run, the BCM would have to signal the PCM over the serial link to turn the fuel pump relay on.

So it takes a very roundabout path, which leaves me shaking my head on this one

Doug

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Attached Files
File Type: pdf 2003_impala_fuel_pump_784627.pdf (20.6 KB, 5 views)
File Type: pdf 2003_impala_ign3_1194126.pdf (33.2 KB, 5 views)
File Type: pdf 2003_impala_ign2_885110.pdf (26.1 KB, 6 views)
File Type: pdf 2003_impala_ign1_885107.pdf (25.0 KB, 7 views)
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Last edited by plano-doug; 10-02-2019 at 11:43 AM.
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post #6 of (permalink) Old 10-03-2019 Thread Starter
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Quote:
Originally Posted by plano-doug View Post
I too think it's kind of weird to send power to the fuel pump on ACC.

Starting at the pump, the PCM controls it via the fuel pump relay.

Looking farther upstream, using the drawings I have access to, I can't find one focused on the ignition switch, but, from what I pieced together, it works as follows:

START and ON both send +12V to the pink wire which goes to both the PCM and BCM.

START and ON also both send +12V to the dark green wire which also goes to both the PCM and BCM.

START also sends +12V to the yellow wire which goes to the PCM.

ACC and ON both send +12V to the brown wire, which goes to the BCM.

(Keep in mind, these connections are sending signals as much as they are sending power.)

START and ON go to the PCM via 3 different wires, but ACC only goes to the BCM. So, for ACC to cause the fuel pump to run, the BCM would have to signal the PCM over the serial link to turn the fuel pump relay on.

So it takes a very roundabout path, which leaves me shaking my head on this one

Doug

.
Thanks Doug, sounds like whenever the BCM gets power from the ignition switch either through ACC or ON, BCM will signal PCM to prime fuel pump, yeah an unusual design that had me confuse.
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