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 P0450: Fuel Tank Pressure (FTP) Sensor Circuit
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 greater than a calibrated amount when vehicle speed is less than 30 km/h (19 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

#### P0450

• | DTC P0100, P0101, P0102, P0103, P0116, P0117, P0118, P0119, P0443, P0449, P0458, P0459, P0498, P0499, P0506, P0507, P050A, P0700, P2227, P2228, or P2229 is not set.

• | The engine is operating.

• | The ambient air temperature is greater than -7°C (+19°F).

• | The vehicle speed is less than 30 km/h (19 mph).

• | The ECM has commanded the EVAP canister vent valve open for greater than 4 seconds.

• | DTC P0450 runs continuously once the above conditions are met for approximately 25 seconds.

#### P0451 Condition 1

• | DTC P0100, P0101, P0102, P0103, P0116, P0117, P0118, P0119, P0443, P0449, P0458, P0459, P0498, P0499, P050A, P0506, P0507, P0700, P2227, P2228, or P2229 is not set.

• | The engine is operating for greater than 1 seconds.

• | The ECM has commanded the EVAP canister vent valve open for greater than 4 seconds.

• | The vehicle speed is less than 10 km/h (6 mph) for greater than 30 seconds.

• | The engine is idling.

• | The ambient air temperature is warmer than -7°C (+19°F).

• | The BARO is greater than 68 kPa.

• | The fuel level is between 11-88 percent.

• | DTC P0451 runs continuously once the above conditions are met for approximately 25 seconds.

#### P0451 Condition 2

• | DTC P0100, P0101, P0102, P0103, P0116, P0117, P0118, P0119, P0443, P0449, P0458, P0459, P0498, P0499, P050A, P0506, P0507, P0700, P2227, P2228, or P2229 is not set.

• | The ECM has commanded the EVAP canister vent valve open.

• | The ECM has commanded the EVAP canister purge solenoid OFF.

• | The BARO is greater than 68 kPa.

• | The fuel level is between 11-60 percent or the fuel level is valid for running the EVAP leak test.

• | The vehicle speed is greater than 10 km/h (6 mph) for greater than 30 seconds.

• | The calculated ambient air temperature is 4-35°C (39-95°F) for greater than 3 seconds.

• | DTC P0451 runs continuously once the above conditions are met for approximately 7 seconds.

### Conditions for Setting the DTC

#### P0450

The ECM detects that the FTP sensor signal oscillates greater than 6.09 mm/Hg (3.26 in. H2O) for 4 seconds, or for a cumulative time of 30 seconds.

#### P0451

• | The ECM detects that the FTP is less than -26.2 mm/Hg (-14.1 in. H2O) or greater than 11.0 mm/Hg (5.9 in. H2O) for 10 seconds or for a cumulative time of 30 seconds.

| OR

• | The ECM detects a change in the zero point of FTP sensor signal greater than +/-5.16 mm/Hg (2.76 in. H2O) from the zero point at start up for 10 seconds, or a cumulative time of 30 seconds.

### Action Taken When the DTC Sets

• | DTC P0450 is Type B DTC.

• | DTC P0451 is Type B DTC.

### Conditions for Clearing the MIL/DTC

• | DTC P0450 is Type B DTC.

• | DTC P0451 is Type B DTC.

### Diagnostic Aids

• | A blocked or clogged EVAP canister vent solenoid valve, or inlet tube may set these DTCs.

• | A stuck open EVAP purge solenoid valve may set these DTCs.

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

Component 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

Control Module References 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. Ignition OFF, disconnect the EVAP purge solenoid valve harness connector.
2. Engine idling, command the EVAP vent valve closed with a scan tool.
3. Increase the engine speed to 1,200-1,500 RPM. Verify the scan tool fuel tank pressure (FTP) sensor parameter is -0.9 to +0.9 mmHg (-0.5 to +0.5 in.H2O).

⇒ | If not within the specified range, replace the EVAP purge solenoid valve.

4. Ignition OFF, 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 .
5. Ignition ON, command the EVAP vent solenoid valve closed with a scan tool.
6. Pressurize the EVAP system with nitrogen to 9.33 mm/Hg (5 in/H2O). Compare the scan tool Fuel Tank Pressure Sensor parameter to the J 41413-200 pressure/vacuum gage. Verify the FTP sensor parameter is within +/-0.9 mmHg (+/-0.5 in.H2O) of the pressure/vacuum gage.

⇒ | If not within the specified range, replace the FTP sensor.

7. Command the EVAP vent solenoid valve OPEN with a scan tool. Verify the scan tool FTP sensor parameter is -0.9 to +0.9 mmHg (-0.5 to +0.5 in.H2O).

⇒ | If not within the specified range, test or replace the EVAP canister vent solenoid valve and vent pipe for a blockage or restriction.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Fuel Tank Pressure Sensor Replacement

• | Evaporative Emission Canister Purge Solenoid Valve Replacement

• | Evaporative Emission Canister Vent Solenoid Valve Replacement

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