DTC P0451 w/o ORVR
Circuit Description
The DTC 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
| • | The barometric pressure is more than 75 kPa. |
| • | The engine coolant temperature is -8 to +110°C (18F-230°F). |
| • | The intake air temperature is more than -8°C (+18°F). |
| • | The fuel tank level is 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 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. |
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.
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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.
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This step determines if a fault is present. The fuel tank pressure sensor reading indicated on the scan tool will vary with the surrounding barometric pressure.
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The FTP sensor voltage will vary with the surrounding barometric pressure.
-
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).
-
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 |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | ||
2 | Did DTC P0450, P0443, P0440, or P0455 set along with DTC P0451? | -- | Go to Step 3 | |
Is the pressure within the specified range? | 0.0-0.9 mm Hg (0.0-0.5 in H2O) | Go to Step 12 | Go to Step 4 | |
4 |
Was any blockage found? | -- | Go to Step 21 | Go to Step 5 |
5 |
Does the voltage equal the specified value? | 5 V | Go to Step 7 | Go to Step 6 |
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? | -- | Go to Step 29 | Go to Step 25 |
7 | Probe terminal 2 of the FTP sensor on the harness side with a test lamp connected to B+. Does the test lamp illuminate? | -- | Go to Step 9 | Go to Step 8 |
8 |
Was a repair necessary? | -- | Go to Step 29 | Go to Step 25 |
Is the voltage within the specified range? | 2.5-2.7 V | Go to Step 10 | Go to Step 26 | |
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? | -- | Go to Step 11 | Go to Step 27 | |
11 |
Was a repair necessary? | -- | Go to Step 29 | Go to Step 25 |
|
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? | -- | Go to Step 13 | Go to Step 28 | |
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 | Go to Step 14 | Go to Step 28 | |
Does the valve hold the vacuum? | 15 in Hg | Go to Step 22 | Go to Step 15 | |
Does the valve hold the vacuum? | 15 in Hg | Go to Step 16 | Go to Step 17 | |
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 | Go to Step 24 |
17 |
Does the test lamp illuminate? | -- | Go to Step 18 | Go to Step 19 |
Did the test lamp illuminate? | -- | Go to Step 23 | Go to Step 20 | |
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? | -- | Go to Step 29 | -- |
20 |
Was a repair necessary? | -- | Go to Step 29 | Go to Step 25 |
21 | Clean the sensor air passage. Is the action complete? | -- | Go to Step 29 | -- |
22 | Inspect the vacuum hoses to the EVAP canister vent valve for restrictions and repair as necessary. Was a repair necessary? | -- | Go to Step 29 | Go to Step 23 |
23 | Replace the EVAP canister vent valve. Refer to Evaporative Emission Canister Vent Solenoid Valve Replacement . Is the action complete? | -- | Go to Step 29 | -- |
24 |
Was a repair necessary? | -- | Go to Step 29 | Go to Step 25 |
25 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 29 | -- |
26 |
Was a repair necessary? | -- | Go to Step 29 | Go to Step 27 |
27 | Replace the FTP sensor. Refer to Fuel Tank Pressure Sensor Replacement . Is the action complete? | -- | Go to Step 29 | -- |
28 | Replace the FTP control valve. Refer to Fuel Tank Pressure Control Valve Replacement . Is the action complete? | -- | Go to Step 29 | -- |
29 |
Does the DTC run and pass? | -- | Go to Step 30 | Go to Step 2 |
30 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |
DTC P0451 w/ORVR
Circuit Description
The DTC 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
| • | The barometric pressure is more than 75 kPa. |
| • | The engine coolant temperature is -8 to +110°C (18-230°F). |
| • | The intake air temperature is -14 to +70°C (7-158°F). |
| • | The fuel tank level is 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.
-
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.
-
This step determines if a fault is present. The fuel tank pressure sensor reading indicated on the scan tool will vary with the surrounding barometric pressure.
-
The FTP sensor voltage will vary with the surrounding barometric pressure.
-
This step verifies that the fuel tank pressure sensor is able to react to EVAP system pressure changes.
-
This step checks the operation of the fuel tank pressure control valve.
-
Clearing the DTCs by removing the DOME fuse also clears the PCM long term memory. Using the scan tool to clear DTCs leaves the long term memory active. DTC emitting diagnostics may not run to completion as expected unless the long term memory is cleared. Removal of the DOME fuse also clears the time display of the radio. 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 a DTC P0451 appears in the Not Ran Since Code Cleared list, the DTC P0451 diagnostic has not yet run. When the 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. 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.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | ||
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 |
Was any problem found? | -- | Go to Step 13 | Go to Step 4 |
4 |
Does the voltage equal the specified value? | 5 V | Go to Step 6 | Go to Step 5 |
5 |
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 |
Was a repair necessary? | -- | Go to Step 18 | Go to Step 14 |
Is the voltage within the specified range? | 2.5-2.7 V | Go to Step 9 | Go to Step 15 | |
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 |
Was a repair necessary? | -- | Go to Step 18 | Go to Step 14 |
|
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. 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).
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 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 18 | -- |
15 |
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 | -- |
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? | -- | System OK | |
