Tool Q&A: What to do with troublesome Toyota EVAP codes

Q: If there is a leak in the system, how does the tech perform a leak check? What leak tests do you begin with?

A: The presence of a leak code does not always mean there is absolutely a system leak, according to Heist at STAR Envirotech. For this reason, diagnostic smoke vapor machines for EVAP system testing are often equipped with a high-quality flow meter.

This component is there as an aid in diagnosing the presence of leakage before moving on to the next step of locating revealed leakage with the aid of visible vapor. For the systems in the model years listed above, to determine the presence of a leak:

1) Connect the diagnostic smoke vapor machine to the EVAP emission system as per manufacturer’s instructions. For example, a typical Toyota EVAP service port has Toyota’s specific instruction label affixed; there are instructions on both sides of the label.

2) Start the machine and observe flow into and through the EVAP system. The ball on the flow meter should be at the very top of the meter, indicating good flow through the system. The vapor fills the system and exits the air drain hose.

3) Seal the EVAP system.

a) Pinch off the air drain hose on the early and/or late types to seal the system. Some systems have the atmospheric vent connected to a plastic tee at the air drain. If so equipped, the hose should be removed and the air drain side should be sealed with a rubber vacuum cap. This allows the vapor pressure sensor to breathe and if it has a small leak, smoke will exit this hose. Otherwise, the smoke will just circulate in the system and no leak will be detected.

b) Close the vent valve on the LEV-II system using the appropriate scan tool with bi-directional control, or by other manual means.

4) With the system sealed, observe the flow meter ball. Once the system flow has stabilized, if the ball is resting at the bottom of the flow meter, there is no flow through the system and therefore leakage is not sufficient to trigger related leak DTCs on the system in its present state. If, at this point, the ball is suspended anywhere in the flow meter range, there is flow through the system and leakage may be sufficient to trigger related leak DTCs. Once it is determined that leakage is present, inspect the system to locate system leak point(s) by virtue of the presence of visible vapor.

Various solutions have been offered to detect very small leaks, such as closing the EVAP vent solenoid and charging the system with CO2, notes Bernie Thompson, president of Automotive Test Solutions. In the system Thompson offers, the Bullseye Leak Detector, the flow gauge is divided into colors that show the size of the leak in the system.

Zachary Parker, president of Redline Detection LLC, notes the system should be tested with a non-dye smoke solution since Toyota forbids the use of dye in the EVAP system. Once the EVAP system has been pressurized, the flow meter will show the flow slowing down or stopping as the pressure equalizes with the smoke machine pressure of just under 0.5 psi. Only a decay gauge that shows no leak down is 100 percent proof of a sealed system with no leaks, Parker says.

A flow meter with the float ball seemingly on the bottom may be allowing some air passage (a slight decay can be observed if there will be an irregular heartbeat of the flow meter indicating there is still a very small leak), notes Rick Escalambre, an automotive technology instructor at Skyline College in San Bruno, CA.

Jason Smith, an educator at Consultants for Automotive Repair Services in San Clemente, CA, notes that smoke testers have improved and increased the accuracy of their flow meters, although technicians should know that this is only a guide and not an absolute when doing EVAP leak diagnosis, especially on a 0.020” leak.

Compressed shop air usually comes with a high moisture content, Smith says. This shop air mixed with a thick smoke solution will weigh a lot more than fuel vapor and will not escape a leak as fast as the vapor will. Therefore, it can be hard to gauge whether the leak on the flow meter will be the same size as the one that the vehicle EVAP system will pick up. It’s up to the technician to discern if what they are looking at is accurate.