Circuit Description
The fuel tank pressure sensor will respond to changes in fuel tank pressure or in vacuum. The signal voltage from the fuel tank pressure sensor to the PCM varies according to changes in fuel tank pressure. The voltage signal can range from a high of over 4 volts to a low of 0.6 volts 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. |
| • | The fuel tank level is between 25 and 75 percent. |
| • | The 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 that is 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 that the diagnostic fails. This information is stored in the Freeze Frame buffer. |
Conditions for Clearing the DTC
| • | The MIL turns OFF after 3 consecutive passing trips without a fault present. |
| • | A History DTC clears after 40 consecutive warm-up cycles without a fault. |
| • | Use the Clear DTC Information function of the scan tool, or disconnect the PCM battery feed in order to clear the DTC. |
Diagnostic Aids
Check for any of the following conditions:
| • | A fuel tank pressure sensor that is shifted 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 the sensor if necessary. |
| • | If DTC P0108, P0113, P0118,P0123, and P0450 are set together, check for an open ground circuit. |
| • | If 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 electrical circuits of the EVAP control system . Inspect the wiring harness and the components for any of the following conditions:
| • | Backed out terminals |
| • | Incorrect mating of terminals |
| • | Broken electrical connector locks |
| • | Incorrectly formed terminals or damaged terminals |
| • | Faulty terminal-to-wire connections |
| • | Physical damage to the wiring harness |
| • | A broken wire inside the insulation |
| • | Corrosion of electrical connections, of splices, or of terminals |
If DTC P0451 cannot be duplicated, the Freeze Frame data can be useful in determining the vehicle operating conditions when the DTC 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 basic checks, and to store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data that was taken when the fault occurred. The information is stored in the scan tool for later reference.
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This step determines if a fault is present. With the fuel tank filler pipe open to the atmosphere, the fuel tank pressure sensor should read near zero. The reading from the fuel tank pressure sensor varies with changes in atmospheric pressure. The specified value in step 2 is typical of the atmospheric pressure near sea level.
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This step determines if the fuel tank pressure sensor is OK. A voltage that is within the specified value indicates that the fault is in the sensor input circuit or in the PCM.
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This step checks the operation of the EVAP canister vent solenoid. The output control of the EVAP canister vent solenoid is disabled if DTCs are stored, if engine speed is indicated, and until the engine reaches an operating temperature of at least 80°C (176°F).
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This step tests for an EVAP canister vent solenoid that is stuck closed or is internally blocked .
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This step checks for an EVAP canister vent solenoid that is stuck open or is leaking .
Step | Action | Value(s) | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | |||||||||
Did the scan tool display indicate fuel tank pressure within the specified value? | 0.0-0.9 mm Hg (0.0-0.5 in H2O) | |||||||||
3 |
Did the test lamp illuminate? | -- | ||||||||
4 |
Is the voltage at the specified value? | 5.0 volts | ||||||||
Was the voltage measured within the specified value? | 2.0-2.6 volts | |||||||||
6 |
Was a repair necessary? | -- | ||||||||
7 |
Was a repair necessary? | -- | ||||||||
8 |
Was a repair necessary? | -- | ||||||||
9 |
Was a repair necessary? | -- | ||||||||
10 |
Was a repair necessary? | -- | ||||||||
11 |
Was a repair necessary? | -- | ||||||||
Did the test lamp illuminate only when the solenoid was commanded ON with the scan tool? | -- | |||||||||
13 |
Was a repair necessary? | -- | ||||||||
14 |
Was a repair necessary? | -- | ||||||||
Does the EVAP canister vent solenoid hold vacuum? | 15 in. Hg | |||||||||
Does the EVAP canister vent solenoid hold vacuum? | 15 in. Hg | |||||||||
17 |
Was a repair necessary? | -- | Go to Diagnostic Aids | |||||||
18 | Replace the fuel tank pressure sensor. Refer to Fuel Tank Pressure Sensor Replacement . Is the action complete? | -- | -- | |||||||
19 | Replace the EVAP canister vent solenoid. Refer to Evaporative Emission Canister Vent Solenoid Replacement . Is the action complete? | -- | -- | |||||||
20 | Replace the PCM. Refer to Powertrain Control Module Replacement . Is the action complete? | -- | -- | |||||||
21 |
Are any DTCs displayed on the scan tool? | -- | Go to the applicable DTC table | System OK |
