Purge valve, how it works, symptoms, problems, testing

Purge valve, how it works, symptoms, problems, testing

What the P0443 code means

P0443 is an OBD-II generic code that the engine control module (ECM) has detected a malfunction with the purge control valve or its control circuit. This could mean an open or short in the valve or circuit.


Vapor Canister Purge Valve Location

Depending on what you drive, there are two typical

Depending on what you drive, there are two typical locations for the vapor canister purge valve.

The Canister purge control valve is most often located in the engine bay on a hose going from the intake to the canister. It can also be located near the fuel tank.

The component won’t look like much. Typically, it’s nothing more than a little black plastic component with an electrical connector and a vacuum line on each end. While it can be hard to identify, it’s usually pretty easy to access once you’ve found it.

Location Of The Purge Valve

Hello, Could Someone Give Me The Location Of The Purge Valve On This Truck? It Has The 4.9 Inline 6 Motor And It Is A 5 Speed Manual

How Much Does It Cost To Fix?

The good news is that having your purge valve fixed won’t break the bank. All in, the cost to repair a broken purge valve will be somewhere between $100 and $200. Most of that cost is in parts, where the average price of a replacement valve can run up to $100.

Connecting the lab scope

Correct functioning of the canister purge valve can be checked by measuring the following signal voltages, see figure 1:

Channel Probe Voltage Range
1 Signal voltage at negative side of canister purge Signal voltage at negative side of canister purge valve 80 V
Ground at battery Ground at battery
2 Power supply at canister purge valve Power supply at canister purge valve 20 V
Ground at battery Ground at battery
Figure 1: Measuring diagram
Figure 1: Measuring diagram

Figure 2: Measuring a working canister purge valve

The lab scope is connected to the canister purge valve via a Measure lead TP-C1812B and Back Probe TP-BP85 and is set to normal scope mode.

Faulty Canister Purge Valve Issues and Symptoms

Be sure to check the symptoms listed below before replacing the canister purge valve. Some of the symptoms can also be related to other faulty vehicle components, though. Therefore, if you aren’t sure the problem actually comes from the purge valve, seeking help from a certified mechanic is always the thing to do.

The Engine has Trouble Starting

A solenoid stuck open might open the way for more air to enter the combustion chamber. When the engine is overflown with air, it might have trouble starting, or it won’t start at all.

Increased Fuel Consumption

When the canister purge valve isn’t functioning correctly, you might notice increased fuel consumption. This happens because the gasoline or diesel fuel simply evaporates, instead of going into the engine. In other words, you will be losing fuel without even burning it.

Rough Idling

Another issue that might arise with a faulty canister purge valve is rough idling. A defective or damaged solenoid might create a vacuum leak. When that happens, more air can enter the combustion chamber, which changes the air-to-fuel ratio.

On older cars, the engine might choke when idling, and sometimes it won’t start at all. On newer vehicles, the engine computer might try to compensate by injecting more fuel, usually causing black smoke to come out of the exhaust system. Nonetheless, the most common symptom will still be rough idle. Instead of choking, though, you might experience a change in engine RPMs.

Worse Performance

On most modern vehicles, the ECU should take care of adjusting the air-to-fuel ratio to keep your engine running. However, you might still experience worse acceleration or at least inconsistent performance.

Check Engine Light

The canister purge valve is directly related to the proper functioning of the motor. Therefore, every time it fails, the ECU will light up the “Check Engine Light” on the dashboard. That said, this light is not always related to the solenoid. The “Check Engine Light” refers to any issue inside the motor that will hinder its performance in some way.

Check Engine Lights can show a minor problem or in
Check Engine Lights can show a minor problem or indicate a larger issue.

On most vehicles, a faulty canister purge valve can trigger any of these codes:

  • P0440: Evaporative Emission Control System Malfunction
  • P0441: Evaporative Emission Control System Incorrect Purge Flow
  • P0443: Evaporative Emission Control System Purge Control Valve Circuit
  • P0444: Evaporative Emission Control System Purge Control Valve Circuit Open
  • P0445: Evaporative Emission Control System Purge Control Valve Circuit Shorted

However, a P0442: Evaporative Emission Control System Leak Detected will usually let you know that one of the vapor hoses is cracked and is leaking instead. In that case, replacing the purge valve would have no effect. Such a problem is fairly common in recent vehicles because of the purge valve being placed to close to the exhaust manifold. Excessive heat will slowly dry out rubber hoses and lead them to crack prematurely. To correct this problem, some car manufacturers have created re-routing components that will relocate the purge valve elsewhere.

For example, this problem was so frequent on older Hyundai Accent that the manufacturers came up with a re-routing kit consisting of longer hoses, a new bracket, and a longer connector allowing mechanics to place the purge valve near the front of the engine instead. If you have such a problem in your car, calling your dealer’s part department might be a good idea before trying to buy new hoses and fix everything up yourself.

Failing Emission Tests

The canister purger valve is linked with vehicle emissions, both directly and indirectly. The direct part is the fuel vapors coming out of the tank. The indirect component is the wrong air-fuel mixture, which can produce more CO2 and hydrocarbons. Naturally, a car that produces more emissions will fail the stringent emission tests performed in recent years. However, if it’s your case, the check engine light should be up in the dashboard and there’s little to no chance to pass an emission test with a check engine light on.

How do you troubleshoot code P0443 ?

NOTE #1: Code P0443 specifically refers to issues in the purge valve control circuit, and leaks in the system, or issues with other EVAP circuits/components will typically not set this code. However, on some Hyundai (mostly Elantra, Santa Fe, Tucson, and Tiburon models) and some VAG models from the early 2000’s, a stuck open purge valve will typically produce code P0441, while on some Mazda products from around the same era, a stuck open purge valve will typically produce code P0446 along with a variety of other EVAP related codes.

NOTE #2: The EVAP purge valve must not be confused with the EVAP vent valve. The primary function of the vent valve is to allow fresh air to enter the system to help displace fuel vapors along sometimes-long vacuum lines towards the engine. Always refer to the manual for the application being worked on to correctly locate the components that are being diagnosed or worked on.

NOTE #3: A repair manual or wiring diagram for the application being worked on, as well as a good quality digital multimeter and a hand-held vacuum pump fitted with a gauge are required items to diagnose code P0443.

Record all codes present, as well as all available freeze frame data. This information can be very useful should an intermittent fault be diagnosed later on. Refer to the notes above if any other codes are present along with code P0443. Bear in mind that if multiple codes are present, they must be diagnosed and resolved in the order in which they were stored. Failure to do this will almost certainly result in a misdiagnosis.

If the code persists after clearing all codes, consult the manual on the location, routing, color-coding, and function of all wiring associated with the purge valve. Perform a thorough visual inspection of all associated wiring; look for damaged, burnt, disconnected, shorted, or corroded wiring and connectors. Make repairs as required, clear all codes, and retest the system to see which codes (if any) return.

NOTE:  Most applications typically require that several drive cycles be completed before EVAP codes can be fully cleared.

If no visible damage is found on the wiring, perform input voltage, ground, continuity, and resistance checks on all associated wiring, but be sure to disconnect the purge valve from the PCM to prevent damage to the controller.

Pay particular attention to the resistance of the purge valve input voltage wire, as well as the signal wire going to the PCM. Resistance values on these wires must match the values stated in the manual exactly. Make repairs, or replace wiring as required to ensure that all obtained readings fall within the manufacturer’s specifications. Clear all codes after repairs are complete, operate the vehicle, and retest the system to see if the code returns.

If the code persists despite having made repairs to wiring, suspect a defective purge valve. There are several ways to test the purge valve’s operation, but removing the valve from the system makes testing the valve considerably easier. Note that while most EVAP purge valves are rated for full battery voltage, there are exceptions to this, so always consult the manual for the correct input voltage before applying direct current to any component.

As a first step in testing the purge valve, test its internal resistance and compare this value with the value stated in the manual, and replace the valve if it does not test within stated specifications. If the resistance checks out, determine the correct input voltage and apply direct current to the valve, but note that the valve must be properly grounded.

On some valves, an audible “click” when current is applied will indicate that the control solenoid in the valve is working, but be aware that the absence of an audible “click” does not necessarily mean that the valve is defective, since some purge valves operate silently.

WARNING: When applying direct current to the purge valve from the vehicles’ battery, make absolutely sure that short circuits cannot happen. Short circuits can destroy the battery as well as the purge valve, in addition to causing serious burns when the test wires overheat. The better option is to use a battery charger to provide current for testing purposes, but whatever the source of the current, consult the manual on the correct procedure to apply direct current to the purge valve solenoid.

Even if the purge valve is known to open and close, how well it works must be tested as well. To do this, attach the vacuum pump securely to one opening of the valve, and draw a vacuum that registers on the gauge.

Purge valves are normally closed, so provided the test equipment is not defective in any way, the vacuum must hold if the valve is in good condition. Keep a close watch on the vacuum gauge- if the vacuum decays the valve is defective, and it must be replaced. If on the other hand, the vacuum does not decay over the space of about 60 seconds, apply direct current to the valve. If the valve works as intended, the vacuum will decay almost immediately: if it does not, the valve is also defective, and it must be replaced as well.

NOTE:  Testing of the purge valve is required because it forms part of the control circuit on the one hand, and for the fact that a defective purge valve can set code P0443 on some applications. Note however that where the code is set by a defective valve, other EVAP related codes are almost certain to be present as well.

Reassemble the EVAP system after all repairs are complete, and operate the vehicle for multiple drive cycles before scanning the system again to see if the code returns.

If the code returns but it is certain that all electrical values fall within specifications, the purge valve works as intended, and that all electrical repairs had been performed to industry standards, it is likely that an intermittent fault is present. Be aware that intermittent faults can be extremely challenging and time consuming to find and repair, and in some cases, it may be necessary to allow the fault to worsen before an accurate and definitive repair can be made.

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NOTE: This information is presented for information purposes only. It is not intended as repair advice and we are not responsible for any actions you take on any vehicle. All information on this site is copyright protected.


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