The Automotive Active Purge Pump An Essential Part of the Modern Vehicle's Emissions Control System
A key component of these systems is the active purge pump. Let's take a closer look at how this pump works and why it's so important.
The Role of the Automotive Active Purge Pump
All gasoline-powered vehicles built after 1996 are equipped with evaporative emission control systems to capture fuel vapors from the gas tank and evaporative system. These vapors are stored in a charcoal canister until purged. The active purge pump plays a vital role in purging these stored fuel vapors from the charcoal canister into the engine for combustion.
During refueling or hot vehicle soak, fuel vapors are pulled from the gas tank and evap lines into the charcoal canister for storage. The purge pump operates periodically to draw these stored fuel vapors out of the charcoal canister and into the engine's intake manifold or exhaust system where they can be burned off during the normal combustion process. This helps to prevent the release of unburnt fuel vapors into the atmosphere from the charcoal canister when the vehicle is being driven.
Construction and Operation of the Active Purge Pump
A typical Automotive Active Purge Pump consists of a brushless DC electric motor and a vacuum-generating piston pump mechanism. The electric motor receives power and ground signals from the vehicle's engine control module (ECM) or powertrain control module (PCM) to operate the pump at specific times.
Inside the pump housing is a spring-loaded pumping chamber with inlet and outlet ports. When the electric motor turns on, it drives an internal offset cam that pushes the pumping piston downward against spring pressure. This creates a vacuum in the pumping chamber and pulls vapors from the charcoal canister into the inlet port.
As the cam rotates further, it allows the spring to push the piston back up. This pressurizes the vapors trapped in the pumping chamber and forces them out the outlet port and into the engine intake manifold or exhaust system for combustion. The ECM controls the on/off cycling of the electric motor to optimize the purging of stored vapors from the charcoal canister.
Importance of an Operational Active Purge Pump
A faulty or non-functioning active purge pump can negatively impact the vehicle's emissions system in a few key ways:
- Stored fuel vapors in the charcoal canister cannot be purged and burned off regularly, causing the canister to reach vapor saturation quicker. This increases the chances of hydrocarbons escaping untreated into the atmosphere from the charcoal canister vent valve.
- With purging not occurring as designed, the ratio of air to fuel entering the engine will be upset. This can trigger trouble codes, cause driveability issues like stalling and rough running, and increase harmful emissions and fuel consumption.
- Over time, excess unburnt fuel can flood the intake manifold and oxygen sensors, affecting the vehicle's ability to maintain proper air-fuel mixture ratios and emission control. This damages catalytic converters and causes the check engine light to turn on.
- Failure of the purge pump to operate as specified means the vehicle no longer meets its EPA emissions certification. Repairs or replacement would be needed to remedy this and restore emissions legality.
Diagnosing Active Purge Pump Issues
Modern scan tools are needed to properly diagnose active purge pump problems based on stored Diagnostic Trouble Codes (DTCs). Common codes that indicate purge pump faults include P0443, P0449, P0455 and P0456. Low voltage or short circuit issues with the electric motor wiring are a typical cause of pump failure.
Symptoms a faulty purge pump can cause include prolonged or permanent check engine lights, rough idle or stalling, fuel odor emanating from the vehicle and reduced fuel economy or power. Low or no vacuum readings at the purge pump outlet port during purge cycle testing confirms a non-functional pump. Replacement of the entire purge pump assembly is usually required to resolve issues.
Proper Purge Pump Maintenance
Routine maintenance like periodic inspections for external leaks or damaged hoses connected to the purge pump helps ensure long-term reliable operation. Replacing old purge pump components at the recommended service intervals in the owner's manual also prevents premature failures from occurring down the road. Using high quality parts is important as well for meeting emissions compliance.
with an increasing focus on reducing greenhouse gas emissions globally, advanced automotive emission controls like active purge pumps will remain an important technology to help vehicles burn fuel more cleanly and efficiently well into the future. Understanding their function helps diagnosis potential problems to keep these systems performing as designed.
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