GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2001 🢒 Tracker - 4WD 🢒 Engine 🢒 Engine Controls - 2.5L (LE8) 🢒 DTC P0451

Circuit Description

The DCT P0451 Fuel Tank Pressure (FTP) Sensor Performance diagnostic checks the accuracy of the FTP sensor signal. The fuel tank pressure sensor responds to changes in the fuel tank pressure or vacuum. The fuel tank pressure sensor signal voltage to the powertrain control module (PCM) varies from a minimum of about 0.2 volts with pressure in the fuel tank to a maximum of more than 4 volts with low pressure in the fuel tank.

Conditions for Running the DTC
    • DTC P1450 and DTC P1451 is not set.
    • The barometric pressure is more than 75 kPa.
    • The engine coolant temperature is between -8°C to +110°C (18°F to 230°F).
    • The intake air temperature is between -14°C to +70°C (7°F to 158°F).
    • The fuel tank level is between 25-75  percent.
    • The fuel tank pressure is more than or less than the atmospheric pressure.
    • The engine has been running at idle for at least 2 minutes.

Conditions for Setting the DTC

The fuel tank pressure is less than -40 mm Hg (-21.41 in H2O) or more than 40 mm Hg (21.41 in H2O) for 5 seconds.

Action Taken When the DTC Sets
    • The PCM illuminates the malfunction indicator lamp (MIL) after 2 consecutive ignition cycles in which the diagnostic runs with the fault active.
    • The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame buffer.

Conditions for Clearing the MIL/DTC
    • The MIL turns OFF after 3 consecutively passing trips without a fault present.
    • A history DTC clears after 40 consecutive warm-up cycles without a fault.
    • Perform the scan tool Clear DTC Information function in order to clear the DTC.

Diagnostic Aids

Check for any of the following conditions:

    • A skewed fuel tank pressure sensor may cause DTC P0451 to set. Compare voltage readings with a known good sensor.
    • A plugged sensor air vent hole. Inspect the sensor and clean if necessary.
    • If a DTC P0451 is intermittent, driving the vehicle under the conditions outlined in the Inspection/Maintenance (I/M) section can verify whether the fault is present. Refer to Inspection/Maintenance Evaporative Emission System Set .

An intermittent malfunction may be caused by a fault in the fuel tank pressure sensor electrical circuit. Inspect the wiring harness and components for an intermittent condition. Refer to Intermittent Conditions .

If a DTC P0451 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining the vehicle operating conditions when the DTC was first set.

Test Description

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

  1. The Diagnostic System Check-Engine Controls prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.

    2.

  2. The fuel tank pressure sensor reading indicated on the scan tool will vary with the surrounding barometric pressure.

    3.

  3. The FTP sensor voltage will vary with the surrounding barometric pressure.

    4.

  4. This step verifies that the fuel tank pressure sensor is able to react to EVAP system pressure changes.

    5.

  5. This step checks the operation of the fuel tank pressure control valve.

    6.

  6. This step determines whether or not the malfunction that caused DTC P0451 is still present. Driving the vehicle under these conditions will verify whether the fault is present. After performing the scan tool Clear DTC Information function, the DTC P0451 diagnostic can be monitored on the scan tool under the Not Ran Since Code Cleared selection in the DTC Information menu. If DTC P0451 appears in the Not Ran Since Code Cleared list, the DTC P0451 diagnostic has not yet run. When DTC P0451 does not appear in the Not Ran Since Code Cleared list, the DTC P0451 diagnostic has run. If the MIL is NOT illuminated and there is no Pending DTC Status in DTC Information, the DTC P0451 diagnostic has passed. The DTCs MUST be cleared in order to view the Current Status of the Not Ran Since Code Cleared list. The DTC Information screen must be checked for Current or Pending status in order to determine the outcome of the diagnostic test involved.

Step

Action

Value(s)

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. Turn OFF the ignition.
  2. Remove the fuel filler cap.
  3. Turn ON the ignition, leaving the engine OFF.
  4. Select the fuel tank pressure (FTP) sensor parameter on the scan tool.

Is the pressure within the specified range?

0.0-0.9 mm Hg (0.0-0.5 in. H2O)

Go to Step 11

Go to Step 3

3
  1. Remove the fuel tank. Refer to Fuel Tank Replacement .
  2. Remove the fuel tank pressure sensor from the fuel tank. Refer to Fuel Tank Pressure Sensor Replacement .
  3. Visually inspect the sensor air vent hole and the air pressure inlet passage for clogging.

Was any problem found?

--

Go to Step 13

Go to Step 4

4
  1. Turn ON the ignition, leaving the engine OFF.
  2. Disconnect the FTP sensor electrical connector.
  3. Measure the voltage on the harness side of terminal 3 of the FTP sensor connector using a DMM.

Does the voltage equal the specified value?

5.0 V

Go to Step 6

Go to Step 5

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

Was a repair necessary?

--

Go to Step 18

Go to Step 14

6

Probe the terminal 2 of the FTP sensor connector on the harness side using a test lamp connected to B+.

Does the test lamp illuminate?

--

Go to Step 8

Go to Step 7

7
  1. Check for an open in the sensor ground circuit between the FTP sensor and the PCM.
  2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 18

Go to Step 14

8

  1. Connect the FTP sensor electrical connector.
  2. Backprobe the connector terminal 1 with the positive lead and connect the negative lead to ground using the DMM.
  3. Measure the voltage with the DMM set to the DC scale.

Is the voltage within the specified range?

2.5-2.7 V

Go to Step 9

Go to Step 15

9

Apply a small amount of vacuum to the FTP sensor while observing the DMM.

Does the voltage decrease when the vacuum is applied?

--

Go to Step 10

Go to Step 16

10
  1. Check for an open in the FTP sensor signal circuit between the sensor and the PCM.
  2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 18

Go to Step 14

11

Caution: Do not breathe the air through the EVAP component tubes or hoses. The fuel vapors inside the EVAP components may cause personal injury.

  1. Remove the fuel tank pressure (FTP) control valve. Refer to Fuel Tank Pressure Control Valve Replacement .
  2. Connect a vacuum hose to the canister side port of the FTP control valve.

    3. Important: There will be some resistance, but air should flow steadily.

  3. Blow air into the hose on the FTP control valve.

Does air flow through the valve to the tank port side?

--

Go to Step 12

Go to Step 17

12

Important: The FTP control valve allows vapor to flow from fuel tank to the canister when the fuel tank pressure is greater than canister pressure by more than 3.5 kPa (0.5 psi).

  1. Connect a hose to the fuel tank port of the FTP control valve.
  2. From the tank side port, blow hard through the valve. Air should flow through the valve out of the canister port.

Does the FTP control valve pass this test?

--

Go to Diagnostic Aids

Go to Step 17

13

Clean the sensor orifice.

Is the action complete?

--

Go to Step 18

--

14

Important: The replacement PCM must be programmed.

Replace the PCM. Refer to Powertrain Control Module Replacement .

Is the action complete?

--

Go to Step 18

--

15
  1. Check for a short in the signal circuit between the FTP sensor and the PCM.
  2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 18

Go to Step 16

16

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

Is the action complete?

--

Go to Step 18

--

17

Replace the FTP control valve. Refer to Fuel Tank Pressure Control Valve Replacement .

Is the action complete?

--

Go to Step 18

--

18

  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 vehicle within the Freeze Frame conditions that set the DTC or until the P0451 diagnostic test has run. Refer to the test description.

Does the DTC run and pass?

--

Go to Step 19

Go to Step 2

19

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