GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2001 🢒 Savana 🢒 Engine 🢒 Engine Controls - 4.3L 🢒 DTC P0452

Circuit Description

The fuel tank pressure (FTP) sensor changes resistance based on the fuel tank pressure, or vacuum. A vacuum is considered negative pressure.

The powertrain control module (PCM) provides a 5-volt reference and a ground. The fuel tank pressure sensor signal varies between ground and 5 volts as the fuel tank pressure varies. The fuel tank pressure sensor voltage increases as the fuel tank pressure decreases, such as negative pressure, or vacuum. The fuel tank pressure sensor voltage decreases, such as positive pressure, or low voltage, as the fuel tank pressure increases. The PCM uses the fuel tank pressure sensor voltage for evaporative emission (EVAP) system leak detection. This DTC sets when the fuel tank pressure sensor signal goes below a predetermined value.

Conditions for Running the DTC

The ignition switch is in the RUN position.

Conditions for Setting the DTC
    • The fuel tank pressure sensor voltage is less than 0.1 volts.
    • All conditions are present for more than 5 seconds.

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

Important: Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM connector gaskets when diagnosing or replacing the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent water intrusion into the PCM.

For an intermittent, refer to Symptoms - Engine Controls .

The EVAP pressure sensor range is from +7.5 in H2O of pressure to -17.5  in H2O of pressure or vacuum.

Inspect for poor connections at connector C152. This connector is located under the underhood electrical center. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

The vacuum and pressure in the EVAP system is measured in inches of water (H2O). Most gauges measure vacuum in inches of mercury (Hg) and pressure in pounds per square inch (psi). The following shows how the values compare:

in H2O

in Hg

psi

1in H2O

0.07 in Hg

0.0361 psi

5 in H2O

0.36 in Hg

0.180 psi

10 in H2O

0.73 in Hg

0.361 psi

15 in H2O

1.10 in Hg

0.541 psi

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. If DTC P1639 sets at the same time, this indicates that the 5.0 voltage reference circuit is shorted to a ground. The 5-volt reference circuit is internally connected within the PCM.

  1. This step determines if the condition is present.

    2.

  2. Using the Freeze Frame/Failure Records data may aid in locating an intermittent condition. If you cannot duplicate the DTC, the information included in the Freeze Frame/Failure Records data can help determine how many miles since the DTC set. The Fail Counter and Pass Counter can also help determine how many ignition cycles the diagnostic reported a pass or a fail. Operate the vehicle within the same Freeze Frame conditions, such as RPM, load, vehicle speed, temperature etc., that you observed. This will isolate when the DTC failed.

    3.

  3. If the scan tool displays 5 volts, the fuel tank pressure sensor signal circuit and the PCM are OK.

    4.

  4. This step determines if the signal circuit is open.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

1

Did you perform the Diagnostic System Check-Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

Did DTC P1639 fail this ignition?

--

Go to DTC P1639

Go to Step 3

3

Important: The ignition must be OFF for a minimum of 15 seconds when you are instructed to turn the ignition OFF. If the ignition switch is not in the OFF position, mis-diagnosis occurs. This information applies to every step that instructs you to turn OFF the ignition.

  1. Turn OFF the ignition for 15 seconds.
  2. Turn ON the ignition, with the engine OFF.
  3. Monitor the fuel tank pressure sensor voltage on the scan tool.

Is the fuel tank pressure sensor voltage below the specified value?

0.10 V

Go to Step 5

Go to Step 4

4

  1. Turn ON the ignition, with the engine OFF.
  2. Review the Freeze Frame/Failure Records data for this DTC and observe the parameters.
  3. Turn OFF the ignition for 15 seconds.
  4. Idle the engine.
  5. Operate the vehicle within the conditions required for this diagnostic to run, and as close to the conditions recorded in the Freeze Frame/Failure Records as possible. Special operating conditions that you need to meet before the PCM will run this diagnostic, where applicable, are listed in Conditions for Running the DTC.
  6. Select the Diagnostic Trouble Code (DTC) option, the Specific DTC option, then enter the DTC number using the scan tool.

Does the scan tool indicate that this diagnostic failed this ignition?

--

Go to Step 5

Go to Diagnostic Aids

5

  1. Turn OFF the ignition for 15 seconds.
  2. Disconnect the fuel tank pressure sensor electrical connector at the fuel tank.
  3. Jumper the fuel tank pressure sensor 5-volt reference circuit to the fuel tank pressure sensor signal circuit at the harness connector.
  4. Monitor the fuel tank pressure sensor voltage using a scan tool.

Is the fuel tank pressure sensor voltage at the specified value?

5 V

Go to Step 13

Go to Step 6

6

  1. Turn OFF the ignition for 15 seconds.
  2. Turn ON the ignition.
  3. Probe the fuel tank pressure sensor signal circuit with the test lamp connected to B+. Refer to Probing Electrical Connectors in Wiring Systems.
  4. Monitor the fuel tank pressure sensor voltage using a scan tool.

Is the fuel tank pressure sensor voltage near the specified value?

5 V

Go to Step 8

Go to Step 7

7
  1. Disconnect the PCM connector C1 located on the same side as the manufacturer logo. Refer to Powertrain Control Module Replacement .
  2. Test the fuel tank pressure sensor signal circuit between the PCM and the fuel tank pressure sensor electrical connector for an open or short to ground.

Is the fuel tank pressure sensor signal circuit open or shorted to ground?

--

Go to Step 10

Go to Step 12

8
  1. Disconnect the PCM connector C1 located on the same side as the manufacturer logo. Refer to Powertrain Control Module Replacement .
  2. Test the 5-volt reference circuit between the PCM and the Fuel Tank pressure sensor electrical connector for an open.

Did you find the 5-volt reference circuit open?

--

Go to Step 9

Go to Step 11

9

Repair the open 5-volt reference circuit. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

--

Go to Step 15

--

10

Repair the open or grounded fuel tank pressure sensor signal circuit. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

--

Go to Step 15

--

11
  1. Inspect the 5-volt reference circuit for a poor connection at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
  2. If you find a poor connection, repair the terminal as necessary. Refer to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 14

12
  1. Inspect the fuel tank pressure sensor signal circuit for a poor connection at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
  2. If you find a poor connection, repair the terminal as necessary. Refer to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 14

13

Important: Inspect for poor connections at the fuel tank pressure sensor before replacing the sensor. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Replace the fuel tank pressure sensor. Refer to Fuel Tank Pressure Sensor Replacement .

Is the action complete?

--

Go to Step 15

--

14

Important: The replacement PCM must be programmed.

Replace the PCM. Refer to Powertrain Control Module Replacement .

Is the action complete?

--

Go to Step 15

--

15
  1. Use a scan tool in order to clear the DTCs.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

--

Go to Step 16

Go to Step 2

16

With a scan tool, observe the stored information, Capture Info.

Does the scan tool display any DTCs that you have not diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK