GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2005 🢒 Century 🢒 DTC 🢒 DTC P0651

Circuit Description

The powertrain control module (PCM) provides 5 volts to the following sensors:

    • The air conditioning (A/C) pressure sensor
    • The fuel tank pressure (FTP) sensor

A circuit condition on one sensor 5-volt reference circuit may affect the other sensor 5-volt reference circuits. The PCM monitors the voltage on the 5-volt reference circuit. If the PCM detects that the voltage is out of tolerance, DTC P0651 sets.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0651 5 Volt Reference 2 Circuit

Conditions for Running the DTC

The Ignition is ON

Conditions for Setting the DTC

The 5-volt reference 1 voltage is more than 4.7 volts or less than 4.4 volts for longer than 15 seconds.

This diagnostic runs continuous.

Action Taken When the DTC Sets
    • The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
    • The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the 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.

Diagnostic Aids
    •  If any sensor using a 5-volt bias voltage, such as the intake air temperature (IAT) sensor or fuel level sensor, is shorted to voltage, DTC P0651 may set in addition to DTC P0641.
    • For an intermittent condition, refer to Testing for Intermittent Conditions and Poor Connections in Wiring System.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

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

1

Did you perform the Diagnostic System Check - Vehicle?

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Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2
  1. Observe the Freeze Frame/Failure Records for this DTC.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. 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.

Does the DTC fail this ignition cycle?

--

Go to Step 3

Go to Diagnostic Aids

3
  1. Turn OFF the ignition.
  2. Disconnect the air conditioning (A/C) pressure sensor.
  3. Turn ON the ignition, with the engine OFF.
  4. Measure the voltage from the 5-volt reference circuit of the A/C pressure sensor to a good ground with a DMM. Refer to Circuit Testing in Wiring Systems.

Is the voltage within the specified range?

4.8-5.2 V

Go to Step 4

Go to Step 5

4
  1. Connect the A/C pressure sensor.
  2. Disconnect the fuel tank pressure (FTP) sensor.
  3. Measure the voltage from the 5-volt reference circuit of the FTP sensor to a good ground with a DMM. Refer to Circuit Testing in Wiring Systems.

Is the voltage within the specified range?

4.8-5.2 V

Go to Testing for Intermittent Conditions and Poor Connections in Wiring System

Go to Step 12

5

Is the voltage measured in the previous step more than the specified value?

5.2 V

Go to Step 8

Go to Step 6

6

Monitor the DMM while disconnecting the FTP sensor.

Does the voltage return to within the specified range when the FTP sensor is disconnected?

4.8-5.2 V

Go to Step 11

Go to Step 7

7
  1. Turn OFF the ignition.
  2. Disconnect the powertrain control module (PCM).
  3. Test the 5-volt reference circuit for a short to ground or any sensor low reference circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 14

Go to Step 13

8

Monitor the DMM while disconnecting the FTP sensor.

Does the voltage return to within the specified range when the FTP sensor is disconnected?

4.8-5.2 V

Go to Step 10

Go to Step 9

9

Test all 5-volt reference circuits for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 14

Go to Step 13

10

Test the FTP sensor signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 14

Go to Step 13

11

Replace the FTP sensor. Refer to Fuel Tank Pressure Sensor Replacement .

Did you complete the replacement?

--

Go to Step 14

--

12

Replace the A/C pressure sensor. Refer to Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement in Heating, Ventilation, and Air Conditioning.

Did you complete the replacement?

--

Go to Step 14

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13

Replace the PCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the replacement?

--

Go to Step 14

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14
  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. 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 15

15

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information

System OK