GM Service Manual Online
For 1990-2009 cars only

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 provides an overview of each diagnostic category.

DTC Descriptors

DTC P0451: Fuel Tank Pressure (FTP) Sensor Performance

DTC P0454: Fuel Tank Pressure (FTP) Sensor Intermittent

Typical Scan Tool Data

FTP Sensor

Circuit

Short to Ground

Open

Short to Voltage

Operating Conditions: Engine operating in Closed Loop at idle

Parameter Normal Range: 0.2-4.8 V

5-Volt Reference Voltage

0 V

0 V

0.7 V

FTP Sensor Signal

0 V

0 V

5 V

Low Reference

--

4.2 V

--

Circuit/System Description

The evaporative emission (EVAP) system is used to store fuel vapors in order to reduce the amount of fuel vapors into the atmosphere. The fuel tank pressure (FTP) sensor is only used for EVAP system diagnostics. The FTP sensor is a transducer that varies resistance according to changes in the fuel tank pressure. The engine control module (ECM) monitors the FTP sensor signal in order to detect vacuum decay and excess vacuum during the EVAP system diagnostic test.

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

FTP Sensor Signal Voltage

Fuel Tank Pressure

High, Approximately 1.5 Volts or More

Negative Pressure/Vacuum

Low, Approximately 1.5 Volts or Less

Positive Pressure

Conditions for Running the DTC

    • The engine is running.
    • DTCs P0451 and P0454 run once an ignition cycle when the above condition is met.

Conditions for Setting the DTC

P0451

The ECM detects the FTP sensor voltage is less than 0.58 volt within 13 seconds after start up.

P0454

The ECM detects an abrupt change in the FTP sensor voltage.

Action Taken When the DTC Sets

DTC P0451 and P0454 are Type B DTCs.

Conditions for Clearing the MIL/DTC

DTC P0451 and P0454 are Type B DTCs.

Diagnostic Aids

If a shared 5-volt reference circuit is shorted to ground or shorted to a voltage, other 5-volt reference circuits may be affected.

Reference Information

Schematic Reference

Engine Controls Schematics

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Special Tools

    • J 41413-200 Evaporative Emissions System Tester (EEST)
    • GE-41415-50 Fuel Tank Cap Adapter
    • J 41413-300 EVAP Cap and Plug Kit

Circuit/System Testing

  1. If DTC P0454 is set Inspect for an intermittent and for a poor connection at the FTP sensor and the engine control module (ECM).
  2. 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 .
  3. Important: The EVAP vent solenoid valve will not remain closed when commanded ON with positive pressure applied to the EVAP system.

  4. Disconnect the EVAP vent line from the vent solenoid, and seal it, using the correct plug from the J 41413-300 .
  5. Pressurize the EVAP system with nitrogen to 5 inches H2O. Compare the Fuel Tank Pressure Sensor parameter with a scan tool to the J 41413-200 pressure/vacuum gage. The scan tool FTP sensor parameter should be within 1 inch H2O of the pressure/vacuum gage.
  6. If the FTP sensor parameter is not within 1 inch H2O of the pressure/vacuum gage, replace the FTP sensor.
  7. Command the purge solenoid valve OPEN with a scan tool.
  8. If the FTP sensor parameter is not 0 inch H2O, replace the FTP sensor.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Fuel Tank Pressure Sensor Replacement
    •  Control Module References for ECM replacement, setup, and programming