|Trouble Code||Fault Location||Probable Cause|
|P0451||Evaporative emission (EVAP) pressure sensor range/performance problem||EVAP pressure sensor|
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What Does Code P0451 Mean?
The evaporative emissions control system, typically referred to simply as “EVAP,” is a system developed to keep fuel vapors from escaping into the atmosphere. Using a system of tubes and valves, the EVAP system routes fuel vapors from the fuel tank into the charcoal canister for temporary storage. Under certain circumstances, while the engine is running, the EVAP system then routes fresh air through the charcoal canister, flushing fuel vapors into the engine to be burned.
The ECM (engine control module) controls the EVAP system. Part of the EVAP system self-test is to verify that system pressure rises and falls as expected, or that the system holds pressure when it is sealed, using a pressure sensor. If the ECM detects an unexpected pressure reading, such as still holding a vacuum when the system is purging, it will detect this as a fault, set a DTC (diagnostic trouble code) in system memory, and illuminate the MIL (malfunction indicator lamp). DTC P0451 is defined as Evaporative Emission Control System Pressure Sensor Range/Performance.
What are the common causes of code P0451 ?
Depending on year, make, and model, DTC P0451 may have number of causes. Here are some of the most common.
- Gas Cap – This is the most common fault. If the gas cap is left off or the car is refueled with the engine running, the EVAP system will not hold pressure during the self-test. Install or replace the gas cap with an OEM or Genuine part.
What are the symptoms of code P0451 ?
Aside from the MIL, you probably won’t notice any drivability symptoms. If the system is stuck open, there may also be fuel trim codes saved alongside the EVAP system codes. You may also notice excessive fuel odor at times other than refueling.
How do you troubleshoot code P0451 ?
A Range/Performance code will be set when either a sensor or other component does not perform within the range the ECM expects to see, given data from other sensors and what the ECM is expecting on certain commands. The EVAP system pressure sensor may or may not be the fault in this instance, so it is important to consider the entire EVAP system, including tubes, vents, solenoids, and valves, etc. It should be noted that EVAP systems are tedious to diagnose and repair.
- Gas Cap Check – This is usually the first thing to check.
- If the gas cap is loose or you refueled with the engine running, reset the DTCs and install the gas cap properly.
- If the gas cap gasket is not sealing, replace the gas cap and reset the DTCs. You may want to consider an OEM (original equipment manufacturer) or Genuine (Ford, Toyota, etc.) gas cap, as some aftermarket gas caps may fit but not function properly for your EVAP system.
- EVAP System Check
- Check that all EVAP system tubes and hoses are connected and intact. Repair as needed.
- Check that all EVAP connectors are fully seated. Repair as needed.
- Pressure Check – If your scan tool has live data capabilities, check the pressure sensor signal.
- Driving around, you should be able to note when the pressure rises and falls when the EVAP system holds and purges. If there is no change, an EVAP purge or canister vent valve could be stuck open or closed.
- Remove the gas cap, the pressure sensor should drop to atmospheric pressure – 0 PSIg or 14.7 PSIa (pounds / square inch gauge or absolute) or 760 mmHg (millimeters mercury). If it does not match or is very slow to react, the sensor could be blocked.
- Professional Diagnosis – If you do not have a live-data-streaming scan tool, and you’ve exhausted your other options, such as the gas cap and making sure all hoses are connected properly, your only recourse may be seeing professional assistance. In-depth analysis and smoke-machine diagnosis may reveal the fault.
Codes Related to P0451
P0450 Evaporative Emission Control System Pressure Sensor Malfunction
P0452 Evaporative Emission Control System Pressure Sensor Low Input
P0453 Evaporative Emission Control System Pressure Sensor High Input
P0454 Evaporative Emission Control System Pressure Sensor Intermittent
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