Diagnostic Instructions
| • | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
| • | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
| • | Diagnostic Procedure Instructions provide an overview of each diagnostic category. |
DTC Descriptor
DTC P0451: Fuel Tank Pressure (FTP) Sensor PerformanceDiagnostic Fault Information
Circuit | Short to Ground | High Resistance | Open | Short to Voltage | Signal Performance |
|---|---|---|---|---|---|
FTP Sensor Low Reference | -- | P0446, P0451 | P0446 | -- | P0451 |
FTP Sensor Signal | P0452 | -- | P0452 | P0453 | P0451, P0454 |
FTP Sensor 5-Volt Reference | P0452, P0530, P0641 | P0451 | P0446, P0452 | P0453, P0530, P0641 | -- |
Typical Scan Tool Data
Circuit | Normal Range | Short to Ground | Open | Short to Voltage |
|---|---|---|---|---|
FTP Sensor Low Reference | -- | 1.5 V | 4.6 V | -- |
FTP Sensor Signal | 1.5 V | 0 V | 0 V | 5 V |
FTP Sensor 5-Volt Reference | -- | 0 V | 0 V | 5 V |
¹ With EVAP system vented to atmosphere | ||||
Circuit/System Description
The fuel tank pressure (FTP) sensor measures air pressure or vacuum in the evaporative emission (EVAP) system. The control module supplies a 5-volt reference and a low reference circuit to the FTP sensor. The FTP sensor signal voltage varies depending on EVAP system pressure or vacuum. The controller also uses this FTP signal to determine atmospheric pressure for use in the engine-off small leak test, DTC P0442. Before using this signal as an atmospheric reference it must first be re-zeroed.
Conditions for Running the DTC
| • | DTC P0451 runs only when the engine-off natural vacuum small leak test, P0442, executes. |
| • | The number of times this test runs can range from 0-2 per engine-off period. The length of the test can be up to 10 minutes. |
Conditions for Setting the DTC
This DTC will set if the controller is unable to re-zero the FTP sensor voltage within a calibrated range during the engine-off small leak test, P0442.
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A current DTC, Last Test Failed, clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Clear the MIL and the DTC with a scan tool. |
Diagnostic Aids
| • | A restriction in the EVAP canister or vent lines could prevent fuel vapor pressure from bleeding off fast enough. If the vent system cannot bleed off pressure fast enough, the re-zero procedure may not complete successfully, which could cause this code to set. By using the purge solenoid command on a scan tool, vacuum can be applied to the system instead of pressure. With the EVAP canister vent solenoid valve open and the EVAP canister purge solenoid valve commanded to 100 percent, the vacuum should not increase to more than 9 inches H2O. |
| • | Ensure that the reference port on the FTP sensor is unobstructed. |
| • | An FTP sensor that is skewed or does not have a linear transition from low to high may cause this code to set. Scan Tool Output Controls, Snapshot, and Plot functions can help detect erratic sensor response. To test the sensor signal under vacuum conditions, use the Quick Snapshot and the Purge/Seal functions to capture data while commanding purge to 20 percent, then plot the data to look for erratic sensor operation. A similar test can be done for the pressure side of the sensor operation by applying pressure with the J 41413-200 Evaporative Emission System Tester (EEST) while taking a snapshot. |
| • | A full fuel tank may cause misdiagnosis. |
| • | When using the electronic EEST to apply pressure, you can regulate the amount of pressure by activating the remote switch ON and OFF while observing pressure in the EVAP system using a scan tool. |
Reference Information
Schematic Reference
Connector End View Reference
Electrical Information Reference
Scan Tool Reference
Special Tools Required
J 41413-200 Evaporative Emission System Tester (EEST)
Circuit/System Verification
Ignition ON, observe the scan tool fuel tank pressure (FTP) sensor parameter. The reading should be between 1.3-1.7 volts with the fuel cap removed, and change with fuel tank pressure.
Circuit/System Testing
- Ignition OFF, disconnect the harness connector at the FTP sensor.
- Ignition OFF, test for less than 5 ohms of resistance between the low reference circuit terminal A and ground.
- Ignition ON, test for 4.8-5.2 volts between the 5-volt reference circuit terminal C and ground.
- Verify the scan tool FTP sensor parameter is less than 0.1 volt.
- Install a 3A fused jumper wire between the signal circuit terminal B and the 5-volt reference circuit terminal C. Verify the scan tool FTP sensor parameter is greater than 4.7 volts.
- If all circuits test normal, test or replace the FTP sensor.
| ⇒ | If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the control module. |
| ⇒ | If less than the specified range, test the 5-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the control module. |
| ⇒ | If greater than the specified range, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the control module. |
| ⇒ | If greater than the specified range, test the signal circuit terminal B for a short to voltage. If the circuit tests normal, replace the control module. |
| ⇒ | If less than the specified range, test the signal circuit for short to ground or an open/high resistance. If the circuit tests normal, replace the control module. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for powertrain control module (PCM) replacement, setup, and programming |
