GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2001 🢒 Catera 🢒 DTC 🢒 DTC P0450

Circuit Description

The fuel tank pressure (FTP) sensor is mounted to the sending unit at the top of the fuel tank. The FTP sensor measures the pressure changes within the evaporative emissions (EVAP) system. The fuel tank pressure sensor has a 5-volt reference circuit, a ground circuit, and a signal circuit.

The fuel tank pressure sensor contains a diaphragm that changes resistance as the pressure in the EVAP system changes. When the EVAP system pressure is low or in a vacuum during purge, the sensor output voltage is low. When the system pressure is high, the sensor output voltage is high.

Conditions for Running the DTC

Part 1

Test continuously.

Part 2

    • The engine is at idle.
    • The engine coolant temperature (ECT) at start is less than 33°C (91°F).
    • The engine is running between 2-10 seconds.

Conditions for Setting the DTC

Part 1

    • The tank pressure is more than 22.50 mm Hg (12.05 in. H2O).
    • The above condition is met for at least 5 seconds

OR

    • The tank vacuum is more than -22.03 mm Hg (-11.80 in. H2O).
    • The above condition is met for at least 5 seconds.

Part 2

    • The tank pressure is more than 7 mm Hg (3.76 in. H2O).
    • The above condition is met for at least 3 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
    • Use the J 35616 Connector Test Adapter Kit for any test that requires probing the ECM harness connector or a component harness connector.
    • Inspect for a condition that may cause excess pressure in the fuel tank such as a restricted vent or sticking EVAP vent solenoid.
    • Refer to Intermittent Conditions if the condition is not present at this time.

Test Description

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

  1. The FTP sensor shares the 5-volt reference with the mass air flow (MAF) sensor and accelerator pedal position (APP) sensor 1. A short to ground or to voltage on the 5-volt reference circuit will set a DTC P0100 along with the DTC P0450. These circuit conditions are diagnosed in the table for DTC P0100.

    2.

  2. The FTP sensor signal circuit is pulled up to 5 volts in the ECM.

    3.

  3. The ECM provides the reference ground for the FTP sensor. A small amount of voltage will appear on this circuit when the ECM is operational. The measured resistance of the circuit will increase when the ECM is operational. This is considered normal.

    4.

  4. Disconnecting the ECM C2 connector will prevent the engine controls power relay from operating. When testing for a short to voltage on an ECM circuit, this relay should be energized.

    5.

  5. The only circuit fault that should be present at this point is an open circuit. A short to ground or voltage on the 5-volt reference circuit should set a DTC P0100.

DTC P0450 Fuel Tank Pressure Sensor Circuit

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

With a scan tool, view the DTC information.

Is a DTC P0100 also set?

--

Go to DTC P0100

Go to Step 3

3
  1. Turn ON the ignition, with the engine OFF.
  2. Remove the fuel filler cap.
  3. Using the scan tool, monitor the fuel tank pressure volts.

Is the voltage within the specified range?

2.2-2.8 V

Go to Step 4

Go to Step 7

4

Important: Before continuing with the diagnosis, zero the EVAP pressure and vacuum gauges on the J 41750 EVAP Pressure/Purge Cart. Refer to the tool operating instructions.

  1. Connect the J 41750 to the EVAP service port.
  2. Replace the fuel filler cap.
  3. Command the vent valve closed using a scan tool.
  4. Pressurize the EVAP system to the specified value with the pressure/purge cart. Monitor the pressure with the gauge on the cart.
  5. Observe the fuel tank pressure volts with the scan tool.

Is the voltage within the specified range?

28 mm Hg (15 in H2O)

4.5-4.9 V

Go to Step 5

Go to Step 7

5
  1. Turn ON the ignition, with the engine OFF.
  2. Move the fuel tank pressure sensor electrical connector, the harness and the ECM connector (by hand only) while observing the scan tool display.

Is the fuel tank pressure volts affected by moving the harness or connectors?

--

Go to Step 18

Go to Step 6

6
  1. Turn ON the ignition, with the engine OFF.
  2. Review the Freeze Frame data for this DTC and note the parameters.
  3. Clear the DTCs.
  4. Turn OFF the ignition for 15 seconds.
  5. Start the engine.
  6. Operate the vehicle within the Conditions for Running the DTC, and close to the data observed in the Freeze Frame/Failure Records.
  7. Check for any DTCs.

Did the DTC fail this ignition?

--

Go to Step 7

Go to Diagnostic Aids

7
  1. Turn OFF the ignition.
  2. Disconnect the fuel tank wiring harness connector C400.
  3. Turn ON the ignition, with the engine OFF.
  4. Using a DMM, measure the voltage from the fuel tank pressure sensor 5-volt reference circuit to a known good ground.

Is the voltage within the specified range?

4.7-5.3 V

Go to Step 8

Go to Step 17

8

Measure the voltage from the fuel tank pressure sensor signal circuit to a known good ground.

Is the voltage within the specified range?

5.5-5.8 V

Go to Step 9

Go to Step 12

9

    Important: Make sure the ECM has shut down prior to measuring the reference ground circuit resistance. This can be verified by the loss of communication with the scan tool.

  1. Turn OFF the ignition for 30 seconds.

    2. Important: Do not use a test lamp to test the continuity of the reference ground. Damage to the ECM will result.

  2. Measure the resistance from the reference ground circuit of the FTP sensor to battery ground.

Is the resistance less than the specified value?

5 ohms

Go to Step 15

Go to Step 10

10
  1. Disconnect the ECM connector C2.
  2. Test the reference ground circuit of the FTP sensor for an open or high resistance.
  3. Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 24

Go to Step 11

11

Measure the resistance from the ECM case to battery ground.

Is the resistance less than the specified value?

5 ohms

Go to Step 21

Go to Step 19

12

Is the voltage more than the specified value?

5.8 V

Go to Step 14

Go to Step 13

13
  1. Turn OFF the ignition.
  2. Disconnect the ECM connector C2.
  3. Test the signal circuit of the FTP sensor for an open or a short to ground.
  4. Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 24

Go to Step 21

14
  1. Turn OFF the ignition.
  2. Disconnect the ECM connector C2.
  3. Turn ON the ignition, with the engine OFF.
  4. Install a fused jumper wire from the control circuit of the engine controls power relay to ground.
  5. Test the signal circuit of the FTP sensor for a short to voltage.
  6. Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 24

Go to Step 21

15
  1. Access the FTP sensor. Refer to Fuel Tank Pressure Sensor Replacement .
  2. Test each of the circuits in the fuel tank wiring harness to the FTP sensor for the following conditions:
    3. • Open
    • High resistance
    • Short to ground
    • Short to the other circuits in the fuel tank wiring harness
  3. Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 24

Go to Step 16

16

  1. Reconnect the fuel tank wiring harness connector C400.
  2. Disconnect the ECM connector C2.
  3. Turn ON the ignition, with the engine OFF.
  4. Install a fused jumper wire from the control circuit of the engine controls power relay to ground.
  5. Test the signal circuit for the FTP sensor for a short to voltage.
  6. Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 24

Go to Step 20

17

  1. Test for an open in the 5-volt reference circuit for the FTP sensor.
  2. Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 24

Go to Step 21

18

Repair the harness or connections as necessary. Refer to Connector Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 24

--

19

Repair the open or high resistance in the ECM ground circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 24

--

20

Test for a poor connection or poor terminal tension at the fuel tank pressure sensor harness connector. 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 24

Go to Step 22

21

Test for a poor connection or poor terminal tension at the ECM harness connector. 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 24

Go to Step 23

22

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

Did you complete the replacement?

--

Go to Step 24

--

23

Important: 

   • Perform the idle learn procedure when replacing the ECM or the throttle body.
   • This vehicle is equipped with a theft deterrent system which interfaces with the engine control module (ECM). Program the new ECM with the frequency code of the theft deterrent module that is currently on the vehicle.

Replace the ECM. Refer to Engine Control Module Replacement .

Did you complete the action?

--

Go to Step 24

--

24
  1. Use the 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 25

Go to Step 2

25

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