|Code||Fault Location||Probable Cause|
|P0444|| Evaporative emission (EVAP) canister purge valve open circuit |
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|Wiring open circuit, EVAP canister purge valve, ECM|
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What Does Code P0444 Mean?
OBD II fault code P0444 is defined as “Evaporative Emission Control System Purge Control Valve Open Circuit”, and is set when the PCM (Powertrain Control Module) detects a malfunction in the circuit that controls the purge valve in the EVAP (Evaporative Emission Control) system, or sometimes a malfunction of the purge valve itself. Typical EVAP systems consist of the fuel tank, fuel filer cap, fuel lines, vacuum lines, a charcoal canister, various pressure and flow sensors, control solenoids, and electrical wiring/connectors.
The function of the EVAP system is to capture fuel vapors before they can escape into the atmosphere. Once captured, fuel vapors are routed through a charcoal canister via vacuum lines to the engine to be burned as part of the air/fuel mixture. Note that fuel vapors will typically not be fed into the system during idling, or when the load on the engine, and therefore fuel demand, is steady. As a general rule, fuel vapors will only be fed to the engine when the demand for fuel increases, or when the vapor pressure in the EVAP system exceeds predefined levels.
Fluctuations in the flow or pressure in the EVAP system are converted into varying signal voltages by the EVAP pressure sensor, which signals the PCM uses to make adjustments to fuel trim to ensure the optimum air/fuel mixture (14.7 parts of air to 1 part of fuel) at all times. For instance, when the purge valve is commanded open to allow fuel vapors to enter the engine (thus enriching the air/fuel mixture), the change in the exhaust gas composition is immediately “noticed” by the #1 oxygen sensor.
Changes in the exhaust gas composition (increased oxygen levels in this case) are transmitted to the PCM in the form of changing signal voltages, which the PCM will use to either reduce the fuel vapor flow, or close the purge valve altogether to maintain, or restore the optimum air/fuel ratio.
Thus, when a malfunction occurs in the purge valve control circuit and the PCM cannot control the purge valve, code P0444 will be set as a result. Note that on some applications a single failure will set the code, while on others, several fault cycles may be required before a code is set and a warning light is illuminated.
Also note that malfunctions of the EVAP purge valve control circuit can prevent the PCM from completing self-diagnostic tests of the system, which tests include measuring the rate at which an induced vacuum or pressure decays. Failure by the PCM to complete self-tests will also set code P0444.
The image below shows a simplified schematic drawing of a typical EVAP system. Note the location of the purge valve in relation to other major components of the system.
NOTE: Open Circuit means that a component or sensor in a system is deprived of the reference voltage it needs to work. Causes of open circuits are many and varied, but for the most part, this type of code is caused by broken wiring, poor connections across electrical connectors or previously repaired wiring, loss of ground that prevents current flow, blown fuses, defective relays, faulty switches, or any of a host of other issues and problems that prevents the flow of current through wiring.
What are the common causes of code P0444 ?
Typical causes of code P0444 could include any or all of the following-
- Damaged, burnt, shorted, or corroded wiring and/or connectors.
- Open circuits.
- Purge valve stuck in the open position.
- Failed, or failing PCM. Note however that this is rare event, and the fault must be sought elsewhere before any controller is replaced.
NOTE: Although code P0444 is rarely caused by issues other than wiring problems and defects in the valve itself, there is one notable exception to this. On early 2000’s Dodge Ram trucks, this code can be set by a short circuit in the seat belt warning chime circuit, since this circuit shares a fuse with both the CD changer and the EVAP system. This is a common problem, so consult the relevant manual on the correct procedure to prevent a continual recurrence of the problem.
What are the symptoms of code P0444 ?
In many cases, there may be no symptoms present other than a stored trouble code and an illuminated warning light. However, typical symptoms vary between applications; below are some typical symptoms that may, or may not be present-
- In the absence of an illuminated warning light, code P0444 may be displayed as a pending code.
- A strong odor of fuel may be present.
- If the purge valve is stuck open for whatever reason, the idle quality may deteriorate, the engine may run rough at some throttle settings, or the engine may even stall unpredictably.
- On some applications fuel consumption may increase.
How do you troubleshoot code P0444 ?
NOTE #1: Code P0444 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 P0444.
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 P0444. 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 P0444 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.