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Codes P0651 and P0449

Tiny
LOUIS W NAGY
  • MEMBER
  • 2003 CHEVROLET SILVERADO
  • 4.3L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 150,000 MILES
5 volt reference #2 circuit short to ground. 5 volt reference circuit FTP shorted to voltage. Symptoms, not getting fire to plugs, intermittently, A/C compressor not getting power. I need a pin out of PCM, a wiring diagram of ignition system, fuel system and A/C system. Fuel pump has been replaced, injectors have been replaced, timing chain replaced. Also new distributor and module. Any suggestions on where to start first? I don’t have a bidirectional scanner or a decent manual.
And when I do find a diagram the font is so small it is hard to read (hard getting old).
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Wednesday, October 9th, 2019 AT 8:07 AM

14 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Good afternoon,

The 651 could either be the AC pressure sensor, if the AC does not work or a failed PCM.

Does the engine run normally?

The 449 is a vent valve in the back of the truck. I posted pictures and a procedure.

Roy

P0651
Descriptor
Probable Causes
Air Conditioning (A/C) Pressure Sensor
Fuel Tank Pressure (FTP) Sensor
Powertrain Control Module (PCM)

P0449
Descriptor
Probable Causes
Evaporative Canister Vent Solenoid
Powertrain Control Module (PCM)

REMOVAL PROCEDURE

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1. Raise and suitably support the vehicle. Refer to Vehicle Lifting.
2. Disconnect the evaporative emission (EVAP) canister vent valve electrical connector (1).

ImageOpen In New TabZoom/Print

3. Remove the EVAP canister vent valve bracket bolt.
4. Remove the EVAP pipe from the clips (1).
5. Disconnect the EVAP vent pipe (4) from the EVAP canister.
6. Remove the EVAP canister vent valve and pipe from the vehicle.
7. If necessary, disconnect the EVAP vent pipe (3) from the EVAP canister vent valve (2).
8. If necessary, detach the EVAP canister vent valve (2) from the bracket.
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Wednesday, October 9th, 2019 AT 9:26 AM
Tiny
LOUIS W NAGY
  • MEMBER
  • 55 POSTS
At this point I have found the throttle position sensor wiring. Signal wire is shorted to 12 volts. What I need is pin out of PCM. This is my second attempt to reply not sure if it went through the first time.
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Thursday, October 10th, 2019 AT 6:14 AM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Cannot have 12 volts. It is a 5 volt sensor. Can you retest.

Do you have a actuator motor on the throttle body

Roy
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Thursday, October 10th, 2019 AT 6:19 AM
Tiny
LOUIS W NAGY
  • MEMBER
  • 55 POSTS
An engine management wiring diagram would be helpful. Also, with this I am sure I could ring out wires and bypass this short, with this and pin out of PCM. Thanks
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Thursday, October 10th, 2019 AT 6:22 AM
Tiny
LOUIS W NAGY
  • MEMBER
  • 55 POSTS
Roy, my reading is correct this is problem: Circuit two is shorted out to positive 12 volts this is my problem., If you could please send me a pin out of the PCM I could ring out the wires and bypass where it is shorting out at. I know what to do I just need the pin out.
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Thursday, October 10th, 2019 AT 8:00 AM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Here are the pin outs for the PCM.

Roy
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Thursday, October 10th, 2019 AT 9:07 AM
Tiny
LOUIS W NAGY
  • MEMBER
  • 55 POSTS
Thanks, now if you could send me the wiring diagram of the engine management system hopefully I’ll have enough to go on to bypass the wires to the necessary sensors according to info I pulled up trouble codes. Net circuit 2 is serving the following sensors, accelerator petal sensor #1, throttle position sensor #1 and 2 and crank sensor. Could you please take a look at the engine diagram to see if this would give me the diagrams I need to follow through from these sensors to
PCM. Thanks for all your help.
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Thursday, October 10th, 2019 AT 11:04 AM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Wiring diagram attached.

Roy
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Saturday, October 12th, 2019 AT 12:29 AM
Tiny
LOUIS W NAGY
  • MEMBER
  • 55 POSTS
Roy you're the greatest. Really appreciate all your help. Told my friends in our Corvette Club, they were impressed. Thanks again
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Saturday, October 12th, 2019 AT 2:13 PM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
You are welcome.

Always glad to help.

Roy
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Saturday, October 12th, 2019 AT 4:59 PM
Tiny
LOUIS W NAGY
  • MEMBER
  • 55 POSTS
Could you send as separate pages as pdf I could print? Thanks
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Sunday, October 13th, 2019 AT 11:38 AM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
I sent you the pin out of the PCM that had pin numbers and wire colors.

They are ready to print.

What exactly do you need for the rest?

Roy
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Sunday, October 13th, 2019 AT 2:14 PM
Tiny
LOUIS W NAGY
  • MEMBER
  • 55 POSTS
The last diagrams you sent where what I needed, but I could not make the font large enough when I printed it out. Could you maybe brake it down into 2 pages as pdf and let’s see if that works? My wife struggled with it and had no luck. Thanks
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Monday, October 14th, 2019 AT 3:57 AM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Okay, I enlarged the diagrams and attached them.

Roy
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Monday, October 14th, 2019 AT 5:29 PM

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