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 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: 02 V-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 ECM supplies a 5-volt reference and a low reference circuit to the FTP sensor.

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 ignition is ON and the engine is running.

### Conditions for Setting the DTC

#### P0451

The ECM detects the FTP sensor voltage is less than 0.58 volt within 13 seconds of 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

#### Connector End View Reference

• | Engine Control Module Connector End Views

• | Engine Controls Connector End Views

#### 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 41413-200 Evaporative Emissions System Tester (EEST)

• | GE-41415-50 Fuel Tank Cap Adapter

### Circuit/System Testing

1. If DTC P0454 is set, inspect for an intermittent and for a poor connection at the FTP sensor.
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. Seal the system using the Purge Seal function with a scan tool.
4. Pressurize the EVAP system with nitrogen to 10 inches H20. 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 H20 of the pressure/vacuum gage.

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

5. 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 engine control module replacement, setup, and programming