P0451

DTC P0451

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) provides an overview of each diagnostic category.



DTC Descriptor
DTC P0451
- Fuel Tank Pressure (FTP) Sensor Performance




Typical Scan Tool Data






Circuit/System Description

The control module monitors the fuel tank pressure (FTP) sensor signal in order to detect vacuum decay and excess vacuum during the evaporative emission (EVAP) diagnostic test. The control module supplies a 5-volt reference and a low reference circuit to the FTP sensor. This DTC sets if the engine control module (ECM) detects one of the following conditions:

* The FTP sensor signal voltage is not within a calibrated range on a cold start-up.
* The FTP sensor signal oscillates greater than a calibrated amount when vehicle speed is less than 30 km/h (50 mph).


The following table illustrates the relationship between FTP sensor signal voltage and the EVAP system pressure/vacuum.






Conditions for Running the DTC

* DTC P0100, P0101, P0102, P0103, P0116, P0117, P0118, P0119, P0125, P0449, P0498, P0506, P0507, P0700, P2227, P2228, or P2229 is not set.
* The engine is operating for greater than 1 second.
* The ambient air temperature is greater than -7°C (19°F).
* The vehicle speed is between 10-30 km/h (6-19 mph).
* The ECM has commanded the EVAP canister vent valve open for greater than 3 seconds.
* DTC P0451 runs continuously once the above conditions are met for approximately 25 seconds.



Conditions for Setting the DTC

* The ECM detects that the FTP is less than -11.9 inches H2O (-22.2 mm Hg) or greater than 6 inches H2O (11.2 mm Hg) for 4 seconds or for a cumulative of 50 seconds.
* The ECM detects that the FTP sensor signal oscillates greater than 3.26 inches H20 (6.09 mm Hg) from a zero point for 4 seconds, or for a cumulative of 50 seconds. The zero point may vary and the vehicle speed must be between 10-30 km/h (6-19 mph) for this test.



Action Taken When the DTC Sets

DTC P0451 is Type B DTC.


Conditions for Clearing the MIL/DTC

DTC P0451 is Type B DTC.


Diagnostic Aids

* A blocked or clogged EVAP canister vent may set this DTC.
* A large leak in the EVAP system could cause this DTC to set.



Reference Information
Schematic Reference

Engine Controls Schematics (Electrical Diagrams)
Connector End View Reference

Component Connector End Views (Connector Views)
Description and Operation

Fuel System Description (Fuel System Description)
Electrical Information Reference

* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions (Diagnostic Trouble Code Descriptions)
Scan Tool Reference

Control Module References (Programming and Relearning) for scan tool information
Special Tools

* J 41413-SPT High Intensity White Light
* J 41413-VLV EVAP Port Vent Fitting Tool
* J 41413-200 Evaporative Emissions System Tester (EEST)
* J 41413-300 EVAP Cap and Plug Kit
* CH-48096 EVAP Service Port Access Tool
* GE-41415-50 Fuel Tank Cap Adapter



Circuit/System Testing

1. Remove the fuel fill cap. Connect the GE-41415-50 to the fuel tank filler neck. Connect the J 41413-200 to the GE-41415-50 .
2. Seal the system using the Purge Seal function with a scan tool.
3. Pressurize the EVAP system with nitrogen to 5 inches H20. Compare the Fuel Tank Pressure Sensor parameter to the J 41413-200 pressure/vacuum gage. The FTP sensor should be within 1 inch H20 of the pressure/vacuum gage.

• If the FTP is not within 1 inch H20 of the pressure/vacuum gage, replace the FTP sensor.

4. Command the vent solenoid valve OPEN with a scan tool.

• If the FTP sensor parameter is not 0 inch H20, replace the FTP sensor.




Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

* Fuel Tank Pressure Sensor Replacement (Service and Repair)
* Control Module References (Programming and Relearning) for ECM replacement, setup, and programming