Technical Description of OBD-II Trouble Code
Range/Performance Issue with Evaporative Emission Control System Pressure Sensor
What does that signify?
This diagnostic trouble code (DTC) is a generic powertrain code that is applicable to OBD-II equipped vehicles (such as Dodge, Ram, Ford, GMC, Chevrolet, VW, Audi, Toyota, etc.). While it is a generic code, the specific repair steps may vary depending on the make and model of the vehicle.
If your OBD-II vehicle is displaying a code P0451, it means that the powertrain control module (PCM) has detected a malfunction in the pressure sensor circuit of the evaporative emissions (EVAP) system.
The EVAP system uses a vented reservoir (commonly known as a canister) to store excess fuel vapors until the engine is operating under the appropriate conditions to burn them completely. Its purpose is to capture fuel vapors before they are released into the atmosphere.
The EVAP system relies on several crucial components for its operation, including the charcoal canister, EVAP pressure sensor, purge valve/solenoid, vent control valve/solenoid, and a complex network of metal tubes and rubber hoses that extend from the fuel tank to the engine compartment.
When fuel is stored, the fuel vapor pressure acts as the propellant, causing the vapors to flow through a network of metal tubes and rubber hoses until they reach the canister. The fuel storage tank vapors are then discharged through the pressure relief valve at the top of the fuel tank and forced through a complex system of metal and rubber lines to the charcoal canister, where they accumulate. The canister contains a charcoal element that absorbs fuel vapors and holds them until they are released at the appropriate time.
The purge control valve/solenoid is responsible for regulating the intake vacuum to the EVAP canister, allowing fuel vapors to be drawn into the engine when conditions are ideal for them to be burned instead of being released into the atmosphere. The PCM controls the purge control valve/solenoid electronically, making it the central component of the EVAP system.
The PCM monitors the EVAP system/fuel tank pressure using the EVAP pressure sensor, which is located in the fuel tank and integrated into the fuel pump/fuel level sending unit housing. Accessing the EVAP pressure sensor can be quite challenging. If the PCM detects that the EVAP and/or fuel tank pressure is not within the pre-programmed range over a set period of time and under certain circumstances, it will store a code P0451 and illuminate the malfunction indicator lamp (MIL).
Other related evaporative emission trouble codes include P0450, P0452, P0453, P0454, P0455, P0456, P0457, P0458, and P0459.
Symptoms
The symptoms associated with this code may include:
Causes
Possible causes for this code to be set are:
Diagnostic and Repair Procedures
When diagnosing a code P0451, you will need a diagnostic scanner, a digital volt/ohmmeter, a reliable vehicle information source like All Data DIY, and possibly a smoke machine.
Start by visually inspecting the EVAP system hoses and lines, as well as the electrical harnesses and connectors. Pay close attention to components that are routed near sharp edges or hot exhaust components. This is also a good opportunity to remove the fuel cap and inspect the seal. Ensure that you screw it back on properly.
Next, connect the scanner to the vehicle’s diagnostic port and retrieve all stored codes and freeze frame data. Take note of this information as it can be helpful later in the diagnosis. Clear the codes and test drive the vehicle until it enters OBD-II readiness mode or the code is reset. EVAP codes usually require multiple drive cycles before they are reset.
Use the diagnostic stream on the scanner to observe the EVAP pressure sensor signal. If the system pressure is within the manufacturer’s recommended specifications, it indicates that the condition has been rectified by tightening or replacing the fuel cap.
Since this is a pressure sensor circuit code, it is advisable to test the EVAP pressure sensor before conducting a smoke test. Testing the EVAP pressure sensor can be challenging as it is typically located at the top of the fuel storage tank. Gain access to the sensor and follow the manufacturer’s recommendations for testing. Replace the sensor if it fails to comply with the specifications.
If the EVAP pressure sensor appears to be functioning properly, unplug all related controllers and test individual circuits using the DVOM. Replace any open or shorted circuits as necessary.
Additional diagnostic notes:
