Auto Systems and Repair: P0451 - OBD-II Trouble Code
OBD II Fault Code
- OBD II P0451
Fault Code Definition
- Evaporative Control System Pressure Sensor Range/Performance
What does this mean? The Code P0451 indicates that the Evaporative Pressure Sensor is indicating pressure change values that are not within specification, during the EVAP Monitor test and/or the operation of the vehicle.
Want to learn more?
The evaporative control (EVAP) system captures any raw fuel evaporating from the fuel storage system (e.g. the fuel tank, filler neck, and fuel cap). Under precise operating conditions—dictated by engine temperature, speed, and load—the EVAP system stores and purges these captured fuel vapors back into the combustion process. The Fuel Tank Pressure Sensor is a device that tracks any positive or negative pressure changes in the Fuel Storage or Evaporative Control (EVAP) system. It constantly relays this pressure information to the Powertrain Control Module (PCM). The Fuel Tank Pressure Sensor is located on top of the Fuel Tank, or on or near the Fuel Pump and Fuel Gauge Module.
- Check Engine Light will illuminate
- In most cases, there are no adverse conditions noticed by the driver
- In some cases, there may be a noticeable fuel odor caused by the release of fuel vapors
Common Problems That Trigger the P0451 Code
- Defective Fuel Tank Sending Unit
- Defective or damaged Fuel Tank
- Defective Fuel Tank Pressure Sensor, wiring, or computer
- Defective Carbon Canister
- Defective Canister Vent Valve - in some cases
- Fuel Cap
- Evaporative Purge Valve
- Evaporative Vent Valve
Polluting Gases Expelled
- HCs (Hydrocarbons): Unburned droplets of raw fuel that smell, affect breathing, and contribute to smog
The Fuel Tank Pressure Sensor is a device that tracks any positive or negative pressure changes in the Fuel Storage or Evaporative Control (EVAP) system. It constantly relays this pressure information to the Powertrain Control Module (PCM). The Fuel Tank Pressure Sensor is located on top of the Fuel Tank, or on or near the Fuel Pump and Fuel Gauge Module.
P0451 Diagnostic Theory for Shops and Technicians
The Evaporative Control System Pressure Sensor Range/Performance code sets when the readings of the Pressure Sensor are irrational and/or out of range for ten seconds of vehicle operation after a cold start. This code uses "two trip" logic, which means that the fault condition must be present during two successive cold starts and vehicle operation.
Common Tests for the Evaluating the Fuel Tank Pressure Sensor
- Retrieve the code and write down the freeze frame information to be used as a baseline to test and verify any repair.
- Pay very close attention to the Fuel Tank Pressure readings by observing its data stream on a scan tool. Does the Fuel Tank Pressure Sensor work properly? If it doesn't, the system will think that no vacuum is being created when, in fact, there is a vacuum being created that the Fuel Tank Pressure Sensor is unable to read. The Fuel Tank Pressure Sensor is the primary feedback sensor that the Powertrain Computer relies on for the leak test data.
- Inspect and test the Fuel Pressure Sensor wiring. Verify that there is a 5-volt reference signal from the PCM, a good ground, as well as a good signal return circuit to the PCM.
- While observing the data stream change (or lack there of) on a scan tool, test the Pressure Sensor with a Vacuum Gauge while it is connected to the wiring harness.
- If all of the above test results are within spec, then the problem may reside in the PCM itself.