Rick's Free Auto Repair Advice


P0443 Evaporative Emission Control System Purge Control Valve Circuit Malfunction

Most common cause of a P0443

The key to diagnosing a P0443 is in its definition: Evaporative Emission Control System Purge Control Valve Circuit Malfunction. That means the computer has detected a circuit issue. That can be an open in the purge valve solenoid windings, a short to ground in the valve’s windings, a bad or corroded electrical connector to the valve or a wiring harness issue.

In many cases, it’s a bad purge valve. But there are also many instances where the problem is in the electrical connector or harness. In my experience, you should always check the condition of the electrical connector first, before automatically replacing the purge valve.

I recommend checking for corrosion on the pins in the connector, bent pins or signs of rodent damage on the insulation in the wiring harness.

If the connector and harness look good, you can use a multimeter to check for good power and ground by following the test procedure in the shop manual. If power and ground check out, then replace the purge valve.

How the purge valve works

If you have P0443 Evaporative Emission Control System Purge Control Valve Circuit Malfunction, read this article. The evaporative emission control system checks to make sure there are no leaks in the lines that run from the gas tank to the charcoal canister and up to the engine. It also checks to make sure the gas cap is sealing correctly.

When you fill your car with gas, the vapors in the tank get forced into a canister filled with activated charcoal. Also, on a hot day as the gas heats up and vaporizes, those same vapors push into the canister where they’re stored. But the charcoal can only hold so much vapor. At some point it has to be emptied. The emptying process is called “canister purge.” Here’s how it works.

The computer orders a canister purge by powering open a PURGE solenoid. That opens the vacuum line between the canister and the intake manifold. At the same time, it opens a VENT solenoid. That allows fresh air into the canister. So the engine is literally sucking out the gas vapors and purging the canister with fresh air. The computer has to adapt its fuel strategy to take advantage of all the extra gas vapors coming into the engine.

The computer notices the canister is empty when it detects a leaner condition (all the vapors are used up) and it resumes normal fuel delivery. Some car manufacturers then close the VENT solenoid but leave the PURGE solenoid open. That creates a vacuum throughout the entire fuel storage system. Once the correct vacuum is reached, it closed the PURGE solenoid and waits to see if the vacuum holds. If it doesn, the system passes the test. If it detects a leak, it sets a code.


To learn more about EVAP system, read this article


© 2012 Rick Muscoplat

Posted on by Rick Muscoplat

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