Circuit Description
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 according to changes in fuel tank pressure. The voltage signal can range from a high of over 4 volts (pressure in the tank) to a low of 0.6 volts (high vacuum condition in the tank) when the vent solenoid is closed.
Conditions for Running the DTC
| • | Engine coolant temperature is 70°C to 110°C (158°F to 230°F). |
| • | Intake air temperature is -10°C to 50°C (14°F to 122°F). |
| • | Barometric pressure is greater than 75kPa. |
| • | Fuel tank level is between 25 and 75%. |
| • | Engine has been running at idle for at least 2 minutes. |
| • | Fuel tank pressure is lower than a specified value after the completion of the EVAP system leakage check. |
Conditions for Setting the DTC
The fuel tank pressure indicated is lower than a specified value after the completion of the EVAP system leakage check.
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL) after two 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 three consecutively passing trips without a fault present. |
| • | A History DTC clears after 40 consecutive warm-up cycles without a fault. |
| • | Use the scan tool Clear DTC Information function or disconnect the PCM battery feed in order to clear the DTC. |
Diagnostic Aids
Check for any of the following conditions:
| • | A shifted (incorrectly calibrated) fuel tank pressure sensor may cause a DTCP0451 to set. Compare voltage readings with a known good sensor. |
| • | A plugged sensor air vent hole. Inspect the sensor and clean if necessary. |
| • | When a DTC P0108, P0113, P0118, P0123 and P0450 are set together check for an open ground circuit. |
| • | When a DTC P0107, P0122 and P0450 are set together check for an open reference circuit. |
| • | A faulty electrical connection at the PCM. |
For functional checks of the EVAP control system components, refer to Evaporative Emission Control System Diagnosis .
An intermittent malfunction may be caused by a fault in the EVAP control system electrical circuits. Inspect the wiring harness and components for any of the following conditions:
| • | Backed out terminals. |
| • | Improper mating of terminals. |
| • | Broken electrical connector locks. |
| • | Improperly formed or damaged terminals. |
| • | Faulty terminal to wire connections. |
| • | Physical damage to the wiring harness. |
| • | A broken wire inside the insulation. |
| • | Corrosion of electrical connections, splices, or terminals. |
If a DTC P0451 cannot be duplicated, 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 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 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, and 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 DTC(s) 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 a DTC P0440, P0450, or P0455 set along with the P0451? | -- | Go to the Applicable DTC Table first | ||
3 |
Does the scan tool display the specified value? | 0.0-0.9 mmHg (0.0-0.5 in. H2O) | ||
4 |
Was any blockage found? | -- | ||
5 |
Is the voltage at the specified value? | 5.0 volts | ||
6 |
Was a repair necessary? | -- | ||
7 | Probe terminal 2 of the fuel tank pressure sensor (harness side) with a test lamp connected to B+. Did the test lamp illuminate? | -- | ||
8 |
Was a repair necessary? | -- | ||
9 |
Was the voltage measured within the specified value? | 2.0 to 2.6 volts | ||
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? | -- | |||
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 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 greater than 3.5 kPa (0.5 psi). Did the fuel tank pressure control valve pass both checks? | 15 in. Hg | |||
Does the solenoid hold vacuum? | 15 in. Hg | |||
Did the solenoid hold vacuum? | 15 in. Hg | |||
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? | 0.0 in. Hg | Go to Diagnostic Aids | |
17 |
Did the test lamp illuminate? | -- | ||
Did the test lamp illuminate? | -- | |||
19 | Repair the open or the short in the WHT/BLU wire between terminal 2 and the main relay. Is the action complete? | -- | -- | |
20 |
Was a repair necessary? | -- | ||
21 | Clean the sensor air passage(s). Is the action complete? | -- | -- | |
22 |
Was a repair necessary? | -- | ||
23 | Replace the EVAP canister vent solenoid. Refer to Evaporative Emission Canister Vent Solenoid Replacement . Is the action complete? | -- | -- | |
24 |
Was a repair necessary? | -- | ||
25 | Replace the PCM. Refer to Powertrain Control Module Replacement . Is the action complete? | -- | -- | |
26 |
Was a repair necessary? | -- | ||
27 | Replace the fuel tank pressure sensor. Refer to Fuel Tank Pressure Sensor Replacement . Is the action complete? | -- | -- | |
28 | Replace the fuel tank pressure control valve. Refer to Fuel Tank Pressure Control Valve Replacement . Is the action complete? | -- | -- | |
29 |
Are any DTCs displayed on the scan tool? | -- | Go to the Applicable DTC Table | System OK |
