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For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 1998 🢒 Firebird 🢒 DTC 🢒 DTC P0452 Fuel Tank Pressure Sensor Circuit Low Voltage

Object Number: 218697 Size: LF
Engine Controls Components
Fuel System
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

Circuit Description

The Fuel Tank Pressure sensor changes resistance based on the fuel tank pressure (or vacuum). A vacuum is considered negative pressure.

The PCM provides a 5.0 volt reference and a ground. The Fuel Tank Pressure sensor signal varies between ground and 5.0 volts as fuel tank pressure varies. The Fuel Tank Pressure sensor voltage increases as the fuel tank pressure decreases (negative pressure, or vacuum). The Fuel Tank Pressure sensor voltage decreases (positive pressure, low voltage) as the fuel tank pressure increases. The PCM uses the Fuel Tank Pressure sensor voltage for 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 0.1 volts.
    • All conditions present for greater than 5.0 seconds.

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

Conditions for Clearing the MIL/DTC
    • The PCM turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
    • A last test failed, or current DTC, clears when the diagnostic runs and does not fail.
    • A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
    • Use a scan tool in order to clear the MIL and the DTC.

Diagnostic Aids

The EVAP Pressure Sensor monitors a range from 7.5 in. H2O of pressure to -17.5 in. H2O of pressure (vacuum).

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 volt reference circuit is either shorted to ground or shorted to a voltage. The 5.0 volt reference circuit is internally connected within the PCM. The A/C Refrigerant Pressure sensor may be causing this DTC to set.

  1. This step determines if the malfunction is present.

  2. Using the Freeze Frame and/or Failure Records data may aid in locating an intermittent condition. If you cannot duplicate the DTC, the information included in the Freeze Frame and/or 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 and/or a fail. Operate the vehicle within the same freeze frame conditions (RPM, load, vehicle speed, temperature etc.) that you observed. This will isolate when the DTC failed.

    3.

  3. If the scan tool displays 5.0 volts, the Fuel Tank Pressure sensor signal, 5.0 volt reference circuit, and the PCM are OK.

    4.

  4. If the scan tool displays 5.0 volts, the Fuel Tank Pressure sensor signal circuit and the PCM are OK.

    5.

  5. Disconnecting the PCM allows using the DMM in order to test the continuity of the circuits. This aids in locating an open or a shorted circuit.

Step

Action

Value(s)

Yes

No

1

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

  1. Install a scan tool.
  2. Idle the engine.
  3. Monitor the Diagnostic trouble Code (DTC) Information using the scan tool.

Did DTC P1639 fail this ignition cycle?

--

Go to DTC P1639 5 Volt Reference 2 Circuit

Go to Step 3

3

Monitor the Fuel Tank Pressure sensor voltage using the scan tool.

Is the Fuel Tank Pressure sensor voltage below the specified value?

0.10V

Go to Step 5

Go to Step 4

4

  1. Turn ON the ignition leaving the engine OFF.
  2. Review the Freeze Frame and/or 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. Disconnect the Fuel Tank Pressure sensor jumper harness at the body pass through connector. Refer to

    Outside Left of Rear Floor Pan, Forward of Rear Axle
    Object Number: 490719 Size: MF
    (1)C405B
    (2)I/P wiring harness
    (3)C405C
    (4)Rear wheel speed sensor harness
    in Wiring Systems.
  2. Jumper the 5.0 volt reference circuit and the Fuel Tank Pressure sensor signal circuit together at the body pass through connector (PCM side of harness).
  3. Observe the Fuel Tank Pressure sensor voltage display on the scan tool.

Is the Fuel Tank Pressure sensor voltage near the specified value?

5.0V

Go to Step 11

Go to Step 6

6

  1. Connect the test lamp J 35616-200 between B+ and the Fuel Tank Pressure sensor signal circuit at the body pass through connector.
  2. Observe the Fuel Tank Pressure sensor voltage display on the scan tool.

Is the Fuel Tank Pressure sensor voltage near the specified value?

5.0V

Go to Step 7

Go to Step 9

7

  1. Turn OFF the ignition.
  2. Disconnect the PCM connector C2 located on the same side as the manufacturer's logo. Refer to Powertrain Control Module Replacement/Programming .
  3. Test the 5.0 volt reference circuit for an open or short to ground.
  4. If you find the 5.0 volt reference circuit is open or shorted to ground, repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and repair the condition?

--

Go to Step 19

Go to Step 8

8
  1. Inspect the 5.0 volt reference circuit for a poor connection at the PCM. Refer to Intermittents and Poor Connections Diagnosis in Wiring Systems.
  2. Repair the terminal as necessary. Refer to Repairing Connector Terminals in Wiring Systems.

Did you find and repair the condition?

--

Go to Step 19

Go to Step 18

9
  1. Turn OFF the ignition.
  2. Disconnect the PCM connector C2 located on the same side as the manufacturer's logo. Refer to Powertrain Control Module Replacement/Programming .
  3. Test the Fuel Tank Pressure sensor signal circuit for the following:
    4. • Open circuit
    • Short to ground
    • Short to sensor ground circuit
    • Short to another C1 circuit.
  4. If you find the Fuel Tank Pressure sensor signal circuit is open or shorted to ground, repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and repair the condition?

--

Go to Step 19

Go to Step 10

10
  1. Inspect the Fuel Tank Pressure sensor signal circuit for a poor connection at the PCM. Refer to Intermittents and Poor Connections Diagnosis .
  2. If you find a poor connection repair the terminal as necessary. Refer to Repairing Connector Terminals in Wiring Systems.

Did you find and repair the condition?

--

Go to Step 19

Go to Step 18

11
  1. Inspect for a poor connection at the body pass through connector. Refer to Intermittents and Poor Connections Diagnosis in Wiring Systems.
  2. If you find a poor connection repair the terminal as necessary. Refer to Repairing Connector Terminals in Wiring Systems.

Did you find and repair the condition?

--

Go to Step 19

Go to Step 12

12
  1. Turn OFF the ignition.
  2. Re-connect the Fuel Tank Pressure sensor jumper harness to the body pass through connector.
  3. Lower the fuel tank to gain access to the Fuel Tank Pressure sensor. Refer to Fuel Tank Replacement .
  4. Disconnect the Fuel Tank Pressure Sensor.
  5. Turn ON the ignition leaving the engine OFF.
  6. Jumper the Fuel Tank Pressure sensor 5 volt reference and signal circuit together at the Fuel Tank Pressure sensor connector.
  7. Observe the Fuel Tank Pressure sensor voltage using a scan tool.

Is the Fuel Tank Pressure sensor voltage near the specified value?

5.0V

Go to Step 16

Go to Step 13

13

Measure the Fuel Tank Pressure sensor 5.0 volt reference circuit at the Fuel Tank Pressure sensor connector using the DMM J 39200 .

Does the DMM display a voltage near the specified voltage?

5.0V

Go to Step 14

Go to Step 15

14

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 19

--

15

Repair the open or grounded Fuel Tank Pressure sensor 5.0 volt reference circuit. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

--

Go to Step 19

--

16
  1. Inspect for a poor connection at the Fuel Tank Pressure sensor harness connector.
  2. If you find a poor connection repair the terminal as necessary. Refer to Repairing Connector Terminals in Wiring Systems.

Did you find and repair the condition?

--

Go to Step 19

Go to Step 17

17

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

Is the action complete?

--

Go to Step 19

--

18

Important:: Program the replacement PCM. Refer to Powertrain Control Module Replacement/Programming .

Replace the PCM.

Is the action complete?

--

Go to Step 19

--

19
  1. Select the Diagnostic Trouble Code (DTC) option and the Clear DTC Information option using the scan tool.
  2. Idle the engine at the normal operating temperature.
  3. Select the Diagnostic Trouble Code (DTC) option and the Specific DTC option, then enter the DTC number using the scan tool.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text, if applicable.

Does the scan tool indicate that this test ran and passed?

--

Go to Step 20

Go to Step 2

20

Select the Capture Info option and the Review Info option using the scan tool.

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

--

Go to the applicable DTC

System OK