P0499 – Evaporative emission (EVAP) system, vent control -circuit high

Reinier

By Reinier (Contact Me)
Last Updated 2017-11-08
Automobile Repair Shop Owner

Trouble CodeFault LocationProbable Cause
P0499 Evaporative emission (EVAP) system, vent control -circuit high Wiring short to positive, EVAP valve

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What Does Code P0499 Mean?

OBD II fault code P0499 is a generic code that is defined as “Evaporative Emission System Vent Valve Control Circuit High”, and is set when the PCM (Powertrain Control Module) detects that a part of the EVAP (Evaporative Emission Control System) is not working within design parameters. Note that this code refers specifically to the electrical control circuit of the Evaporative Emission System Vent Valve.

The function of the EVAP system is to capture fuel vapors before they can escape into the atmosphere. In a fully functional system, fuel vapors are collected and passed through a charcoal canister in which the activated charcoal stores the vapors, before being passed to the inlet tract through a network of hoses to be burned as part of the air/fuel mixture when operational conditions allow this to happen.

The vent valve works in conjunction with the charcoal canister to achieve this, with the function of the vent valve being to allow atmospheric air to enter the EVAP system to help displace fuel vapors as the vapor is purged from the system to be combusted in the engine. On almost all applications, the vent valve is normally open, and the application of a 12-volt circuit current closes the valve when the PCM needs to pressurize the EVAP system to test for leaks. Problems in the control circuit or a failure of the vent valve itself will store a trouble code and illuminate a warning light.

Where is the P0499 sensor located?

Note that modern EVAP systems typically consist of the fuel tank, fuel filler cap, pressure and flow sensors, a charcoal canister, vent valve with a control solenoid, purge valve with a control solenoid, fuel and vacuum lines, fuel vapor hoses, and electrical wiring / connectors.

In light of the above, non-professional mechanics should take note that both the appearance and location(s) of the various EVAP system components vary greatly between applications. Therefore, it is imperative that the manual for the affected application always be consulted to locate and identify the correct EVAP system component before an attempt is made to diagnose any code that relates to the EVAP system. Failure to do this will result in wasted time, misdiagnoses, and the unnecessary replacement of parts and components.

The image below shows a simplified schematic representation of a typical EVAP system, but be aware that this diagram only shows the general arrangement of an EVAP system, and not an actual layout of this system on any application.

What are the common causes of code P0499 ?

Some common causes of code P0499 could include the following-

  • Defective EVAP vent valve
  • Burnt, damaged, shorted, or corroded wiring and /or connectors
  • Failed or failing PCM. Note that this is a rare event, and the fault must be sought elsewhere before any control module is replaced

How expensive is it to fix code P0499 ?

If done on a DIY basis, a replacement EVAP vent valve will cost from around $70 to about $200, depending on the application.

Take note thought that if the repair is to be performed professionally at a repair shop, most shops will add labor charges of between 2 and 4 hours to the cost of the part, so shop around for the best labor rates. Note that this repair estimate does not include relevant fees and taxes that may be payable.

What are the symptoms of code P0499 ?

Some common symptoms of code P0499 could include the following-

  • Stored trouble code and possibly an illuminated warning light
  • In some cases, additional EVAP system related codes may be present along with P0499
  • In some cases, it may not be possible to fill the fuel tank to capacity, since the fuel system cannot be vented during filling
  • Depending on the nature of the problem, a strong fuel odor may be present
  • Depending on the nature of the problem, serious driveability issues may develop if the fuel system cannot be vented via the EVAP system. In these cases, an excessive vacuum can develop in the tank that can starve the engine of fuel
  • The vehicle may not pass a compulsory emissions test

What are common solutions to code P0499 ?

Solutions to code P0499 commonly include the following-

  • Inspection, testing, and/or replacement of the EVAP vent valve
  • Inspection and repair/replacement of damaged wiring

How serious is code P0499 ?

Code P0499 is moderately serious in cases where the tank cannot be filled to capacity, since the vehicle can run out of fuel. However, this code becomes more serious if the EVAP remains in the closed position, since the engine can be starved of fuel unexpectedly.

How safe is it to still drive the car with code P0499 ?

Ideally, this code should be resolved without delay due to the fire and health risks posed by escaping fuel vapors. More importantly, though, if any driveability issues are present, these can potentially immobilize the vehicle unexpectedly, which has obvious and serious safety implications if the vehicle is driven in traffic.

How difficult is it to repair code P0499 ?

With only a few exceptions, EVAP codes are moderately to very difficult to diagnose and repair due to the inaccessibility of many EVAP components on most applications. If equipment such a floor jack, properly rated jack stands, and /or vehicle hoist are not available, the better (and safer) option is to refer the affected application to a competent repair facility for professional diagnosis and repair.

Since the purpose of the vent valve is closing off the EVAP system, you will need a vacuum pump with an integrated gauge to diagnose a defective vent valve. You will also need a good quality digital multimeter and a repair manual for the application being worked on to determine the location, routing, function, and color-coding of each wire in the vent valve control circuit.

What are the common mistakes when repairing code P0499 ?

Mistakes when dealing with code P0499 commonly include the following-

  • Failure to resolve codes that precede P0499 before attempting to diagnose P0499
  • Failure to inspect the EVAP vent valves’ air intake or built-in air filter for the presence of restrictions such as mud, nesting insects, or ice in cold climates

How do you troubleshoot code P0499 ?

NOTE #1: The vent valve control solenoid forms an integral part of the control circuit, and as such, its internal resistance must be tested as well.

NOTE #2: If other codes are present along with P0499, follow the rule that says all codes must be diagnosed and resolved in the order in which they were stored. Failure to follow this rule could result in a misdiagnosis. In some cases, most notably on some Nissan and Infinity models, a failed vent valve will trigger code P0455while some GM models will display code P0466. Both codes are caused by dirt entering the vent valve through a broken screen on the vent valve inlet side. Also note that on these models a defective vent valve can make it almost impossible to fill the fuel tank, since the air in the tank cannot be vented.

Step 1

Record all codes present, as well as all available freeze frame data. This information can be of use should an intermittent fault be diagnosed later on.

Step 2

Perform a thorough visual inspection of all associated wiring and connectors. Look for shorted, burnt, damaged, broken, or corroded wiring and connectors. Repair or replace wiring and/or connectors as required. Clear all codes when repairs are completed, and rescan the system to see if the code returns.

Step 3

If no visible damage to wiring is found, perform resistance, ground, and continuity checks on all associated wiring, and compare obtained readings with the values stated in the manual. Pay particular attention to the voltage that reaches the solenoid. Most solenoids require full battery voltage to work, so be sure to check that a low battery charge is not the cause of the problem.

Repair or replace all defective wiring to ensure that obtained readings fall within the ranges specified by the manufacturer. Note that the vent valve control circuit must be disconnected from the PCM during resistance and continuity checks to prevent damage to the controller.

Step 4

If all electrical values fall within specifications, it should be possible to activate the vent valve manually repeatedly with the scanner if the scanner has that capability. Activating the vent valve solenoid repeatedly will often reveal intermittent faults, but note that these types of faults can sometimes be extremely difficult to trace and repair. In extreme cases, it may be necessary to allow the fault to worsen before an accurate diagnosis and definitive repair can be made.

Step 5

If the scanner does not (or cannot) activate the vent valve solenoid, consult the manual on the location of the valve. On some applications the valve is connected to the charcoal canister, while on others, the actual valve may be located some distance away.

Disconnect the valve solenoid from the system, and follow the directions in the manual on the correct procedure to apply battery voltage to the solenoid directly. If the control solenoid is fully functional, there will be an audible click as soon as current is applied. If there is no “click”, the solenoid may be defective, or the solenoid shuttle may simply be stuck. Test the solenoid’s internal resistance, and if it agrees with the value stated in the manual, prepare to remove the solenoid for further testing or replacement.

Step 6

Once the valve and solenoid is removed from the vehicle, attach the vacuum pump to one opening. Note that since vent valve solenoids are normally open, you need to apply battery current to the solenoid so that the valve closes. Make sure that the solenoid is properly grounded during this step.

Draw a vacuum with the pump until the gauge registers a vacuum value within the valve’s operating range. Assuming that the test equipment is not defective in any way, the vacuum will hold steady if the valve closes fully. A decaying vacuum indicates that the valve is leaking, or not closing fully. Replace the valve if it does not hold a vacuum.

NOTE: Note that during normal operation the vent valve contains a pre-defined pressure, and not vacuum. However, since it is easier to test the valve with a vacuum as opposed to a positive pressure, it is important not to exceed the vent valve’s design parameters.

Doing so could result in a false positive result, meaning that a perfectly good valve could be condemned simply because it is expected to perform outside of its design parameters. Use this handy converter to convert the EVAP system’s design pressure to a usable vacuum for testing the vent valve.

Step 7

When replacing, or re-installing the vent valve after testing, it is always a good idea to inspect all associated vacuum lines for signs of damage, cracking, splitting, or other issues. Although vacuum leaks usually trigger codes other than P0499, making sure that all vacuum lines are in good shape is a common-sense preventative measure that could prevent issues and problems later on.

Once the vent valve is replaced or re-installed and all electrical connections are secure, clear all codes and retest the system to see if the code returns. If it does not return after several drive cycles, the repair can be considered as having been successful.

Codes Related to P0499

  • P0498 – “Evaporative Emission System Vent Valve Control Circuit Low”

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