wont srtar

[Mr.RNR]

looking for help. i just did head gaskets on my 2003 silverado, i put it back together and wont star and when start its not running good, i have P0641 code open circuit a what can be?

[nocturnal92]

Probably its PCM.

[canadianVRss]

If it's not the PCM like nocturnal92 said then check for the little grounds near the back of the engine. There's one on the passenger side in the back that loves to get pinched between the head and the block when reinstalling the heads.

[1FASTBRICK]

Check the grounds, especially if the heads were rebuilt and they painted them. The TB plug wires also become brittle and it is possible that 1 of the wires broke.

 

Here is a Diagnostic Trouble tree I found.

 

DTC P0641
Circuit Description
The powertrain control module (PCM) provides a 5-volt reference to the following sensors:

The throttle position (TP) sensor 1
The accelerator pedal position (APP) sensor 2
The engine cooling fan speed sensor
The AC pressure sensor
The fuel tank pressure (FTP) sensor
The oil pressure sensor (OPS)
The PCM monitors voltage on the 5-volt reference circuit. If the voltage is higher or lower than required, DTC P0641 will set.

Conditions for Running the DTC
The ignition is ON.

Conditions for Setting the DTC
The PCM detects a voltage that is higher or lower than required on the 5-volt reference circuit.
The above condition is present for 1 second.
Action Taken When the DTC Sets
The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records.
Conditions for Clearing the MIL/DTC
The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
Clear the MIL and the DTC with a scan tool.
Step
Action
Values
Yes
No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Powertrain Control Module (PCM) Connector End Views or Engine Controls Connector End Views

1
Did you perform the Diagnostic System Check-Engine Controls?
--
Go to Step 2
Go to Diagnostic System Check - Engine Controls

2

Important
If the vehicle has a cranks but will not run condition proceed to step 3.


Observe the Freeze Frame/Failure Records for this DTC.
Turn OFF the ignition for 30 seconds.
Start the engine.
Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.
Did the DTC fail this ignition?
--
Go to Step 3
Go to Intermittent Conditions

3
Turn OFF the ignition.
Disconnect the throttle body electrical connector. Refer to Throttle Body Assembly Replacement .
Turn ON the ignition, with the engine OFF.
Measure the voltage from the 5-volt reference circuit of the throttle position (TP) sensor 1 to a good ground with a DMM.
Is the voltage within the specified range?
4.8-5.2 V
Go to Step 5
Go to Step 4

4
Is the voltage more than the specified value?
5.2 V
Go to Step 8
Go to Step 6

5
Connect the throttle body electrical connector.
Disconnect the air conditioning (A/C) pressure sensor. Refer to Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement in Heating, Ventilation, and Air Conditioning.
Measure the voltage from the 5-volt reference circuit of the A/C pressure sensor to a good ground with a DMM.
Is the voltage within the specified range?
4.8-5.2 V
Go to Step 10
Go to Step 9

6
Monitor the DMM while disconnecting all other devices connected to this 5-volt reference A circuit one at a time.
If voltage changes when one of the above components are disconnected, replace the component. Refer to the appropriate replacement procedure.
Was a component replaced?
--
Go to Step 12
Go to Step 7

7
Test the 5-volt reference A circuit for a short to ground or for any sensor low reference circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct a condition?
--
Go to Step 12
Go to Step 10

8
Turn ON the ignition, with the engine OFF.
Test each 5-volt reference circuit and the fuel tank pressure sensor signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct a condition?
--
Go to Step 12
Go to Step 10

9
Replace the throttle body assembly. Refer to Throttle Body Assembly Replacement .

Did you complete the replacement?
--
Go to Step 12
--

10
Test this 5-volt reference circuit for a short to the TAC motor control 1 or 2 circuits.

Did you find and correct a condition?
--
Go to Step 12
Go to Step 11

11
Replace the powertrain control module (PCM). Refer to Powertrain Control Module (PCM) Replacement .

Did you complete the replacement?
--
Go to Step 12
--

12
Clear the DTCs with a scan tool.
Turn OFF the ignition for 30 seconds.
Start the engine.
Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.
Did the DTC fail this ignition?
--
Go to Step 2
Go to Step 13

13
Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?
--
Go to Diagnostic Trouble Code (DTC) List
System OK

Document ID# 1252378

[Mr.RNR]

thanks for the info, Im going for step 11 because i test the connectors and,

The throttle position (TP) sensor 1 5V
The accelerator pedal position (APP) sensor 2 5V
The engine cooling fan speed sensor 5V
The AC pressure sensor 5V
The fuel tank pressure (FTP) sensor 5V
The oil pressure sensor (OPS) 5V

so next is the pcm.