GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2001 🢒 Savana 🢒 Engine 🢒 Engine Controls - 8.1L 🢒 DTC P0452

Circuit Description

The powertrain control module (PCM) monitors the fuel tank pressure (FTP) sensor signal in order to detect vacuum decay and excess vacuum during the enhanced evaporative emission (EVAP) diagnostic test. The PCM supplies a 5-volt reference and ground to the sensor. The FTP sensor signal voltage increases as the FTP decreases, with negative pressure or vacuum, and high voltage. The FTP sensor signal voltage decreases as the FTP increases , with positive pressure, and low voltage. This diagnostic trouble code. (DTC) sets when the FTP sensor signal goes below a predetermined value.

Conditions for Running the DTC

The engine is running.

Conditions for Setting the DTC
    • The FTP sensor voltage is less than 0.1 volt.
    • All conditions are present for greater 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.

Test Description

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

  1. If DTC P1639 sets, the 5-volt reference may be shorted to ground.

    2.

  2. If the FTP sensor voltage is near 5 volts, the FTP sensor signal and 5-volt reference circuits are OK from the fuel tank harness connector to the PCM.

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

  1. Idle the engine for 1 minute.
  2. Monitor the DTC information with a scan tool.

Did DTC P1639 fail this ignition?

--

Go to DTC P1639

Go to Step 3

3

With the scan tool, observe the FTP sensor voltage.

Does the scan tool indicate that the FTP sensor voltage is less than the specified value?

0.1 V

Go to Step 5

Go to Step 4

4
  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, or within the parameters observed in the Freeze Frame/Failure Records .

Does the DTC fail this ignition?

--

Go to Step 5

Go to Intermittent Conditions

5

  1. Turn OFF the ignition.
  2. Raise the vehicle. Refer to Lifting and Jacking the Vehicle in General information.
  3. Disconnect the fuel tank wiring harness at the fuel tank harness connector. Refer to

    Fuel Pump Wiring
    Object Number: 375609 Size: MF
    (1)C301
    (2)Electronic Brake Control Module (EBCM)
    (3)Fuel Lift Pump
    and Connector End View .
  4. Connect a 3-amp fused jumper wire between the 5-volt reference circuit and the signal circuit of the FTP sensor at the fuel tank harness connector.
  5. Turn ON the ignition, with the engine OFF.
  6. With a scan tool, observe the FTP sensor voltage.

Does the scan tool indicate that the FTP sensor voltage is near the specified value?

5 V

Go to Step 8

Go to Step 6

6

Test the 5-volt reference circuit of the FTP sensor for an open, between the fuel tank harness connector and the PCM. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 12

Go to Step 7

7

Test the signal circuit of the FTP sensor for a short to ground, or an open between the fuel tank harness connector and the PCM. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 12

Go to Step 9

8
  1. Remove the fuel tank. Refer to Fuel Tank Replacement .
  2. Disconnect the EVAP vent valve harness connector.
  3. Inspect the fuel tank wiring harness for the following conditions:
    4. • Damaged wiring
    • Poor connections
    • Broken wires inside the insulation
  4. Repair conditions as necessary. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 12

Go to Step 10

9

Inspect for poor connections at the harness connector of the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 12

Go to Step 11

10

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

Did you complete the replacement?

--

Go to Step 12

--

11

Replace the PCM. Refer to Powertrain Control Module Replacement .

Did you complete the replacement?

--

Go to Step 12

--

12
  1. Use the scan tool in order to clear the DTCs.
  2. Turn OFF the ignition for 30 seconds.
  3. Operate the vehicle within the Conditions for Running the DTC.

Does the DTC run, and pass?

--

Go to Step 13

Go to Step 2

13

Use a scan tool in order to 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