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P0451 Code – What Does It Mean & How To Fix It

This is one of the most frequent OBD2 trouble codes. Read the full article below to know what it means, how to fix it, and what other codes may show related to it.

Definition

P0451 is an OBD-II Code that refers to Evaporative Emission Control System Pressure Sensor Range/Performance

Meaning

A P0451 code is a manufacturer specific code usually found either in Audi, GMC Toyota, Dodge, Ram, Ford and VW vehicles. The EVAP system includes a venter reservoir called “canister,” which is used to collect excessive gas vapors until the engine is operated in the proper circumstances. This reservoir keeps gasoline vapors from seeping into the air.

It means that the pressure is outside the parameters specified by the manufacturer during vehicle operation or an EVAP monitor test and thus the Error Code P0451 is set and will activate the Check Engine light.

Causes

Common causes for this code include:

  • A charcoal canister that is cracked or damaged
  • Faulty EVAP pressure sensor 
  • Fuel Tank is Clogged 
  • Fuel cap is missing or loose
  • Collapsed, or burned EVAP hoses/lines

Symptoms

The symptoms of a P0451  code are:

  • MIL (malfunction indicator lamp) illumination
  • In most cases, there will be no symptoms
  • There may be a slight decrease in fuel efficiency

Diagnosis

To diagnose a P0451 DTC code, a technician would:

  1. Scan for codes in the ECM and look at the freeze frame data for failure. 
  2. Check if fuel cap is loose or missing.
  3. If a code is being set, clear it and recheck to see if the code returns
  4. If not clear check for poor connection or wiring
  5. Inspect all EVAP hoses/lines for damage and leaks 
  6. Remove canister and inspect for cracks 
  7. Replace sensor if readings are not within manufacturer specifications 
  8. Replace canister if it is damaged

Common mistakes

The following are some of the most common mistakes that a technician may make when diagnosing a P0451 code:

  • Not properly identifying the cause of the problem when using Freeze Frame Data 
  • Using an incorrect scan tool when checking for codes 
  • Not checking the vent system thoroughly to identify problems 
  • Leaving the gas cap loose or off, after replacing parts in the emission system can cause a P0451 code to return. 
  • Replacing parts without diagnosing the cause of the P0451 code, will cause return visits to garages for the same problem

How serious is this?

A P0451 code is not a very serious problem. It should not cause a vehicle to be inoperative, but if left ignored for a long time it can cause the Evaporative Emission Control System pressure sensor to wear out and need replacement and the Check Engine Light will remain on.

What repairs can fix the code?

The following are solutions that may fix this problem:

  • Replace damaged or leaking hoses/lines 
  • Canister replacement if it is cracked, broken or defective.
  • Replacing defective or damaged wiring or connectors to the sensors in tank
  • Replace the Evaporative Emission Control System pressure sensor if readings are not within manufacturer specifications. 
  • Replace fuel cap to ensure tightness of the gas cap

Related codes

A P0451 is related to and may be accompanied by the following codes:

P0459, P0450, P0452, P0453, P0454, P0455, P0456, P0457 and P0458.

Conclusion

In conclusion, the P0451 code is a manufacturer specific trouble code that means the pressure in the Evaporative Emission Control System is outside of specifications. It should not be a very serious problem and should be easily fixed with a little diagnosis and some replacement parts.