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 fuel tank pressure or vacuum. The fuel tank pressure sensor signal voltage to the PCM varies from a minimum of about 0.2 volts with pressure in the fuel tank to above 4 volts with a high vacuum situation in the fuel tank (vent solenoid stuck closed).
Conditions for Running the DTC
| • | Engine coolant temperature between 70°C (158°F) and 110°C (230°F). |
| • | Intake air temperature between -10°C (+14°F) and +50°C (+122°F). |
| • | Barometric pressure more than 75 kPa. |
| • | Fuel tank level is between 25 and 75 percent. |
Conditions for Setting the DTC
| • | Engine running at idle for at least 2 minutes. |
| • | Fuel tank pressure is lower than specified value after completion of EVAP system leakage check. |
| • | The EGR system diagnostic has run and passed. |
Action Taken When the DTC Sets
| • | The malfunction indicator lamp (MIL) will illuminate after two consecutive ignition cycles in which the diagnostic runs with the fault active. |
| • | The PCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame buffer. |
Conditions for Clearing the MIL/DTC
| • | The MIL will turn OFF after three consecutively passing cycles without a fault present. |
| • | A History DTC will clear after 40 consecutive warm-up cycles without a fault. |
| • | DTCs can be cleared by using a scan tool or by disconnecting the PCM battery feed. |
Diagnostic Aids
Check for any of the following conditions:
| • | A shifted (incorrectly calibrated) fuel tank pressure sensor may cause a 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 multiple DTCs are set, it may be possible to have an open or shorted reference voltage circuit or an open ground circuit. |
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 circuit. Inspect the wiring harness and components for an intermittent condition. Refer to Intermittent Conditions .
If you cannot duplicate a DTC P0451, the information included in the Freeze Frame data can be useful in determining 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 to 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 the 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 solenoid or a clogged EVAP canister vent solenoid inlet air hose.
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This step performs an EVAP canister vent solenoid test. The EVAP canister vent solenoid 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 an EVAP canister vent solenoid control circuit test. The EVAP canister vent solenoid 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).
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This step checks whether the conditions that caused the DTC P0451 are still present. Driving the vehicle under the following conditions can verify whether the fault is present. After performing the scan tool Clear DTC Information function, road test the vehicle while monitoring the DTC P0451 diagnostic on the scan tool under Not Ran Since Code Cleared. 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. 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 | ||
Did a DTC P0450, P0443, P0440, or P0455 set along with the P0451? | -- | Go to Step 3 | ||
3 |
Does the scan tool display the specified value? | 0.0-0.9 mm Hg (0.0-0.5 in Hg) | Go to Step 12 | Go to Step 4 |
4 |
Did you find any blockage? | -- | Go to Step 21 | Go to Step 5 |
5 |
Is the voltage at the specified value? | 5 V | Go to Step 7 | Go to Step 6 |
6 |
Was a repair necessary? | -- | Go to Step 29 | Go to Step 25 |
7 | Probe terminal 2 of the fuel tank pressure sensor, harness side, with a test lamp connected to B+. Did 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 |
9 |
Was the voltage measured within the specified value? | 2.0-2.5 V | Go to Step 10 | Go to Step 26 |
Apply a small amount of vacuum to the fuel tank pressure sensor while observing the voltage on the DMM. Did the voltage drop when the vacuum was applied? | -- | Go to Step 11 | Go to Step 27 | |
11 |
Was a repair necessary? | -- | Go to Step 29 | Go to Step 25 |
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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 fuel tank pressure 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). Did the fuel tank pressure control valve pass both checks? | 15 in Hg | Go to Step 14 | Go to Step 28 | |
Does the solenoid hold vacuum? | 15 in Hg | Go to Step 22 | Go to Step 15 | |
Did the solenoid hold vacuum? | 15 in Hg | Go to Step 16 | Go to Step 17 | |
16 | While the EVAP canister vent solenoid is still holding vacuum from Step 15, use the scan tool to command the EVAP canister vent solenoid OFF. Did the vacuum drop to the specified value? | 0 in Hg | Go to Diagnostic Aids | Go to Step 24 |
17 |
Did 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 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 passages. Is the action complete? | -- | Go to Step 29 | -- |
22 | Inspect the EVAP canister vent solenoid vacuum hoses for restrictions and repair as necessary. Was a repair necessary? | -- | Go to Step 29 | Go to Step 23 |
23 | Replace the EVAP canister vent solenoid. 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 . Is the replacement complete? | -- | Go to Step 29 | -- |
26 |
Was a repair necessary? | -- | Go to Step 29 | Go to Step 27 |
27 | Replace the fuel tank pressure sensor. Refer to Fuel Tank Pressure Sensor Replacement . Is the action complete? | -- | Go to Step 29 | -- |
28 | Replace the fuel tank pressure control valve. Refer to Fuel Tank Pressure Control Valve Replacement . Is the action complete? | -- | Go to Step 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 | |
