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Diagnosing the cause for an EVAP (evaporative system) leak code that has been set can be one of the most frustrating jobs a tech can face. Unless the fuel cap was obviously left loose or if upon a visual inspection a cracked or disconnected vapor hose is found, diagnosing the EVAP system for vapor leaks can be very time consuming. Evaporative related codes for leaks are the cause of a high number of "comebacks" causing the technician's productivity to decline and the customer to be further inconvenienced while their vehicle is being worked on. By following the steps in this article, quickly finding the leak and re-testing the Evap system prior to releasing the vehicle will help to reduce future comebacks, increase the tech's productivity, boost customer's confidence and increase customer loyalty to the repair facility. See our most popular smoke machine
tester. Also check out OTC's more recent, more compact LeakTamer - OTC 6522
Evaporative System's Effectiveness
As with any system it is important to understand the basics in order to be able to diagnose problems. The purpose of the EVAP system is to minimize the amount of fuel vapors entering the atmosphere. Also it stands to reason that if fuel vapors do not escape the system this will result in higher fuel efficiency as well. The EPA
(Environmental Protection Agency) has conducted a study with the Ford Motor Company on the effectiveness of the OBD II self monitoring system and found the system to be very effective.
The fuel vapors in the EVAP system are stored in a charcoal canister to be purged and burned in the combustion chamber at certain operating conditions. The system is designed to use the fuel vapors by pulling them from the canister with the use of a purge solenoid. With the OBD II self monitoring system, tests are ran by the vehicles PCM (Powertrain Control Module) to insure the EVAP system is functioning as it was designed. If the PCM sees test results outside certain pre-determined parameters or limits a DTC (Diagnostic Trouble Code) will be set causing the MIL (Malfunction Indicator Light) or SES (Service Engine Soon) warning to appear on the dash alerting the driver of a malfunction. In some cases a malfunctioning EVAP system can cause more pollutants to enter the atmosphere than the vehicle's tailpipe emissions.
Evaporative Leak Codes
Although there are many causes for EVAP codes to be triggered, the most common DTC's are for leaks. P0440, P0442, P0455, P0456 and P0457 are among the most common EVAP codes, each indicating a different size leak, sensor malfunction or possibly just the fuel cap left off after refilling. When diagnosing the cause of a code being set, it is advisable to check a repair manual for a specific flow chart for the DTC, make and model being worked on. Also search for TSB's (Technical Service Bulletin's) using a repair manual or on-line database like Mitchel 1 or ALLDATA. Sometimes if the manufacturer has determined there is a problem with a component or PCM software there will be a TSB describing the fault and the solution including updated part numbers if applicable.
First visually inspect the gas cap, fuel tank, filler neck, vapor canister and vapor lines for signs of leaks. EVAP vent solenoids are open on most vehicles with the engine off, however the vent solenoid needs to be in the closed position for smoke testing. To perform a smoke test the vehicle should not be running. Some vehicles allow a handheld scan tool to interface with the vehicle's PCM to close the vent solenoid for leak testing, look in mode 8 with the scan tool to see if this is possible. If the vehicle being worked on does not have this capability a volt meter can be used on most models to close the vent solenoid. Another option is to simply plug the vent hose temporarily while smoke testing, but keep in mind this method will not reveal a faulty solenoid that may not be sealing properly when energized.
1. Unplug the electrical connector from the vent solenoid.
2. With the key in the on position and the engine off, use the voltmeter to find the negative terminal.
3. Plug the connector back to the vent solenoid and rotate the selector on the voltmeter to the Amp position.
4. Back probe the negative side of the electrical plug with the red lead of the meter and connect the black lead to ground. With the key on the solenoid will be closed allowing the EVAP system to be checked.
connect the Evaporative Smoke Tester's lead wires to a 12 volt power source. Hook up the regulated 50-125 PSI inert gas source to the tester. Due to the EVAP system's vapors being flammable, Nitrogen (an inert gas) is the recommended pressure supply, if using the smoke tester for other leak detection purposes like HVAC (Heating Ventilation and Air Conditioning), engine vacuum leaks or exhaust leaks shop air will suffice. Determine if the vehicle being checked is required to meet 1/2 mm (.020") or 1 mm (.040") maximum allowable leakage, most newer vehicles must meet the 1/2 mm (.020") requirement.
On smoke testers like the MotorVac that require using a hose on the machine to determine the position of the pass/fail flag, insert the fitting on the clear
hose from the smoke tester into the the appropriate "Test Standard" or test port on the front of the machine. With the smoke tester dial turned to "Test" or "Meter" depending on the model being used, activate the machine with the handheld switch and align the red flag so it is even with the floating ball, this is the pass/fail line for this vehicle. Connect the clear line to the vehicle's EVAP service port, if a service port is not present use a "T" vacuum line fitting to connect the smoke tester to an EVAP vapor hose. If a smoke machine like the OTC 6525 (see video)
is being used, to determine the pass/fail mark just move the selector to the pass/fail standard and move the red flag to the level of the floating ball (no hose or test standard port needs to be used).
Once the hose is connected to the vehicle's EVAP system, turn the machine on with the handheld switch and watch the flow meter's indicator ball. If the ball floats above the red flag the system has a leak that will fail the self test and set a DTC; if the ball stays below the red flag, the system passes. After completing any leak repair, repeat phase one to insure the quality of the repair.
The EVAP service port on OBD II vehicles was designed with a Schrader valve before smoke testing or visible UV (Ultra Violet) vapor was considered to be a viable method of diagnosing leaks in these systems. Since the smoke vapor condenses partially when passing through the Schrader valve making it less dense when escaping the system, in phase two it is recommended that the schrader valve be removed.
Phase Two is necessary when the vehicle fails the phase one test, which simply means there is a leak determined to be present that is large enough to set a DTC. Remove the clear line from the vehicle's service port, remove the Schrader valve by turning it clockwise, or by-pass this step if using a "T" vacuum fitting. Connect the black visible vapor hose (on OTC6525 there is only a black hose) to the vehicle's EVAP system. Turn the selector on the smoke machine to "Smoke" or "Visible Vapor" depending on the model tester being used and activate the machine with the handheld switch. Remove the fuel cap until smoke can be seen coming out of the filler neck. This allows the smoke to fill the system much faster and insures that a visible vapor will escape at the location of the leak. The vapor has a UV compound that makes it more visible. By using a bright light or an ultra violet light inspect the system for leaking vapors. Once the vapor is seen, the source of the leak is easily determined.
In addition to using the phase one procedure to verify the integrity of the repair, some scan tools have bi-directional controls that can comand the vehicle to perform a self test of the EVAP system (even with the coolant temperatrure above the normal parameter). This test takes between 10 to 20 minutes and is more comprehensive than the phase one procedure since all the components in the system are evaluated.
Related Auto Repair Tools and Information Links
OTC6521 Leak Tamer Smoke Machine EVAP Leak Detector
OTC6525-1 Nitrogen Regulator
EVAP System Vent Problems - Gas Won't go Into Tank
Common EVAP Codes - Car Tools, Tips & Advice
Evaporative leak detection using a smoke machine, visual inspection, including phase one, phase two and the use of a scan tool for verifying...