Circuit Description
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
| • | The barometric pressure is more than 75 kPa. |
| • | The engine coolant temperature is between -8°C and +110°C (18°F-230°F). |
| • | The intake air temperature is more than -8°C (+18°F). |
| • | The fuel tank level is between 25 and 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 change in the fuel tank pressure is less than a specified value after completion of EVAP system leak test.
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. |
| • | When DTCs P0108, P0113, P0118, P0123, and P0450 are set together, check for an open ground circuit. |
| • | When DTC P0107, P0122, and P0450 are set together, check for an open reference circuit. |
If DTC P0451 is intermittent, driving the vehicle under the following conditions can verify whether the fault is present. Perform the scan tool Clear DTC Information function. Road test the vehicle while monitoring the DTC P0451 diagnostic on the scan tool under the Not Ran Since Code Cleared selection in the DTC Information menu. If a DTC P0451 appears in the Not Ran Since Code Cleared list, the P0451 diagnostic has not yet run. When the DTC P0451 does not appear in the Not Ran Since Code Cleared list, the P0451 diagnostic has run. If the MIL is NOT illuminated, and there is no Pending DTC Status in DTC Information, the P0451 diagnostic has passed. The DTCs MUST be cleared in order to view the Current Status of the Not Ran Since Code Cleared list. DO NOT forget that the Not Ran Since Code Cleared list only indicates that the test has run, not whether the test passed or failed. The DTC Information screen must be checked for Current or Pending status in order to determine the outcome of the diagnostic test involved.
An intermittent malfunction may be caused by a fault in the fuel tank pressure sensor electrical circuit. Inspect the wiring harness and components for any of the following conditions:
| • | Any backed-out terminals |
| • | Any improper mating of terminals |
| • | Any broken electrical connector locks |
| • | Any improperly formed or damaged terminals |
| • | Any faulty terminal-to-wire connections |
| • | Any physical damage to the wiring harness |
| • | A broken wire inside the insulation |
| • | Any corrosion of the electrical connections, the splices, or the terminals |
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.
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The Powertrain OBD System Check 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.
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This step determines if a fault is present. Review Freeze Frame data in order to determine the condition of when the DTC set. Always record this information.
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This step verifies that the fuel tank pressure sensor accurately reacts to EVAP system pressure changes. This also checks the sensor signal input circuit.
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This step checks the operation of the fuel tank pressure control valve.
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This step checks the operation of the fuel tank pressure control valve.
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This step checks for a stuck EVAP canister vent valve or a clogged inlet air hose at the EVAP canister vent valve .
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This step performs an EVAP canister vent solenoid test. The EVAP canister vent valve output control is disabled by the PCM when any DTCs are stored, when engine speed is present, or when the engine operating temperature is less than 80°C (176°F).
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This step performs a control circuit test on the EVAP canister vent valve . The EVAP canister vent valve output control is disabled by the PCM when any DTCs are stored, when engine speed is present, and when the engine operating temperature is less than 80°C (176°F).
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | |||
Did DTC P0450, P0443, P0440, or P0455 set along with DTC P0451? | -- | |||
3 |
Is the pressure within the specified range? | 0.0-0.9 mm Hg (0.0-0.5 in. H2O) | ||
4 |
Was any blockage found? | -- | ||
5 |
Does the voltage equal the specified value? | 5.0 V | ||
6 | Check for an open or a short in the 5 volt reference circuit between the FTP sensor and the PCM. Repair as necessary. Was a repair necessary? | -- | ||
7 | Probe terminal 2 of the FTP sensor on the harness side with a test lamp connected to B+. Does the test lamp illuminate? | -- | ||
8 |
Was a repair necessary? | -- | ||
9 |
Is the voltage within the specified range? | 2.0 - 2.7 V | ||
Apply a small amount of vacuum to the FTP sensor while observing the voltage on the DMM. Does the voltage drop when the vacuum is applied? | -- | |||
11 |
Was a repair necessary? | -- | ||
|
Caution: Do not breathe the air through the EVAP component tubes or hoses. The fuel vapors inside the EVAP components may cause personal injury.
Important: There will be some resistance, but air should flow steadily through the valve. Did air flow through the valve to the tank port side? | -- | |||
Important: The FTP control valve will not allow air to flow from the tank side port to the canister side port until the pressure on the tank side is more than 3.5 kPa (0.5 psi). Does the FTP control valve pass both checks? | 15 in Hg | |||
Does the valve hold the vacuum? | 15 in. Hg | |||
Does the valve hold the vacuum? | 15 in. Hg | |||
16 | While the EVAP canister vent valve is still holding the vacuum from Step 15, use the scan tool to command the EVAP canister vent valve OFF. Does the vacuum decrease to the specified value? | 0.0 in. Hg | Go to Diagnostic Aids | |
17 |
Does the test lamp illuminate? | -- | ||
Did the test lamp illuminate? | -- | |||
19 | Repair the open or the short in the BLU/BLK wire between terminal 1 of EVAP canister vent valve and the main relay. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
20 |
Was a repair necessary? | -- | ||
21 | Clean the sensor air passage. Is the action complete? | -- | -- | |
22 | Inspect the vacuum hoses to the EVAP canister vent valve for restrictions and repair as necessary. Was a repair necessary? | -- | ||
23 | Replace the EVAP canister vent valve. Refer to Evaporative Emission Canister Vent Solenoid Replacement . Is the action complete? | -- | -- | |
24 |
Was a repair necessary? | -- | ||
25 |
Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the action complete? | -- | -- | |
26 |
Was a repair necessary? | -- | ||
27 | Replace the FTP sensor. Refer to Fuel Tank Pressure Sensor Replacement . Is the action complete? | -- | -- | |
28 | Replace the FTP control valve. Refer to Fuel Tank Pressure Control Valve Replacement . Is the action complete? | -- | -- | |
29 |
Are any DTCs displayed on the scan tool? | -- | System OK |
