P0443 Code: Evaporative Emission Control System Purge Control Valve Circuit

What the P0443 code means

The purge valve is a solenoid: a coil that, when it receives current, opens the path for the canister vapors to reach the intake. The computer powers it and monitors that circuit electrically.

The P0443 code is stored when the measured current does not match what was expected. It can be an open circuit, when nothing flows, or a short circuit, when more than the right amount flows.

It is important to tell it apart from P0441: that one is a performance code (the vapor does not flow as it should) and this one is a circuit code (the problem is electrical). In practice a faulty valve can set both, but the starting point of the diagnosis is different: here you start with the multimeter, not with the smoke test.

It helps to know how the computer controls this valve, because it affects the measurement. It does not power it continuously but with a modulated signal: it opens and closes many times per second, changing the share of time it stays open, which lets it meter the vapor flow precisely instead of having only two states.

That means measuring voltage with an ordinary multimeter on the control wire gives an average value that can mislead you. To see what is really going on you need an oscilloscope or, as an approximation, the opening percentage the scan tool reports in live data.

P0443 code symptoms

• Check engine light on.
• Rough idle if the valve has stuck open mechanically.
• Gas smell in some cases.
• No click at all when you command the valve with the scan tool.
• The EVAP monitor never reaches ready status.
• A purge percentage that never changes in live data even as engine conditions change.
• Missing click when you command the valve in an active test.

Likely causes of the P0443 code

1. Purge valve coil open internally. The most frequent cause.
2. Connector that is corroded, has backed-out pins or has moisture in it.
3. Power or control wire that is cut or chafed.
4. Blown fuse in the circuit.
5. Short to ground on the control wire.
6. Failed output driver in the computer. Uncommon, and always checked last.
7. Failed internal protection diode in the coil, which alters the measured current without opening the circuit.
8. Control wire with high resistance from internal corrosion under the insulation.
9. Replacement valve not compatible with the vehicle modulated signal.

How to diagnose the P0443 code step by step

1. Unplug the valve and measure its resistance. An infinite reading confirms an open coil. A very low reading points to an internal short.
2. Check that 12 volts reach the power pin with the ignition on.
3. Verify the continuity of the control wire between the valve and the computer.
4. Look for a short to ground by measuring between the control wire and the chassis with the computer connector unplugged.
5. Inspect the connector for green corrosion, moisture and backed-out pins.
6. Wiggle the harness with the engine running and watch whether the code appears intermittently.
7. Check the matching fuse in the engine compartment fuse box.
8. Watch the purge percentage in live data. It should change with load and temperature. A fixed value means the command is not getting through.
9. Measure the signal with an oscilloscope if you can, because a multimeter only shows an average of the modulated signal.
10. Check the voltage drop on the control wire with the valve activated, not just its continuity at rest.

How to fix the P0443 code

• Replace the purge valve when the resistance is out of specification.
• Clean the connector with contact cleaner and apply dielectric grease.
• Repair damaged wiring with solder and heat shrink tubing, routing it away from hot areas and from edges that could chafe it.
• Replace the fuse and find out why it blew before you call the job done.
• Replace the connector if the pins are backed out or corroded beyond saving.
• Replace the whole valve if the internal protection diode has failed, because it cannot be repaired separately.
• Replace the section of wire with internal corrosion instead of splicing it, because the leftover resistance brings the code back.
• Use a replacement that is compatible with the vehicle modulated control, not a generic simple on-off valve.

After the repair, command the valve with the scan tool: you should hear the click clearly. Then clear the P0443 code and confirm it does not return.

Technical reference data

• Typical coil resistance: 20 to 35 ohms. Infinite indicates an open circuit.
• Supply: 12 volts with the ignition on, ground controlled by the computer.
• Acceptable voltage drop on the control wire: below 0.2 volts.
• The valve should make an audible click when it is activated.
• Typical control signal frequency: 10 to 100 Hz depending on the manufacturer.
• Opening percentage in normal operation: from 0 percent at cold idle up to 60 or 80 percent under steady load.

Brand-specific notes

On many vehicles the purge valve is mounted close to the intake manifold, exposed to constant heat. The insulation on its wiring hardens and cracks over the years, and that is the real origin of quite a few codes that get blamed on the valve.

A generic simple on-off purge valve does not properly replace a modulated one. Even if it fits physically and seems to work, the computer will keep detecting a current different from the one it expects.

Frequently asked questions about P0443