For 1990-2009 cars

### 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 Descriptor

DTC P0451: Fuel Tank Pressure (FTP) Sensor Performance

### 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 | 5 V
FTP Sensor Signal | 0 V | 0 V | 5 V
Low Reference | -- | 4.2 V | --

### 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 more 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.

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

• | DTCs P0100, P0101, P0102, P0103, P0116, P0117, P0118, P0119, P0125, P0449, P0498, P0506, P0507, P0721, P0722, P2227, P2228, and P2229 are 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 more 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 more 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

#### Connector End View Reference

• | Engine Control Module Connector End Views

• | Engine Controls Connector End Views

#### Description and Operation

Fuel System Description

#### 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

• | Scan Tool Data List

• | Scan Tool Data Definitions

• | Scan Tool Output Controls

#### Special Tools Required

• | 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 after completing the diagnostic procedure.

• | Fuel Tank Pressure Sensor Replacement

• | Control Module References for ECM replacement, setup, and programming