Technical
EVAP monitor on European cars Real world diagnosis of DMTL systems Chasing down evaporative emission control system (EVAP) fault codes can be difficult and frustrating due to the variety of equipment and strategies on the market. But it’s profitable work if you understand the system. This article focuses on EVAP system diagnosis on European (and some Asian) vehicles equipped with a DMTL (diagnostic module for tank leakage), offering helpful insights for the service of these imported vehicles.
By Jacques Gordon
O
n a business trip several years ago, I was in a country that has no emissions regulations. The hotel parking lot was filled with late-model rental cars, but cars parked on the street were much older and obviously well past their best years. The strong smell of gasoline on those sun-baked streets made it obvious that a functioning evaporative emission control system (EVAP)
was not important there. That smell also provided a dramatic example of just how effective our modern EVAP systems are. Our federal emissions regulations require that EVAP systems be tested for leaks as frequently as possible by on-board test equipment. The malfunction indicator light (MIL) will turn on if a leak is detected, and it will also turn on if any faults are detected in the leak testing equipment. All EVAP systems work basically the same way to capture and store fuel tank vapors, but car makers have devised several different methods for on-board leak testing. Given the variety of on-board test equipment and strategies, chasing down EVAP fault codes can be difficult and frustrating. But it’s important work that can be profitable if you understand the system. Here we’ll discuss the on-board test used on almost all European cars and also on a few Asian models, too.
On-board test The DMTL (diagnostic module for tank leakage) is a Bosch part that includes the air pump, switching valve, reference orifice and heater. The outlet is connected to the charcoal canister.
When the powertrain control module (PCM) tests the EVAP system for leaks, it measures one of three parameters; pressure, time or current draw. About half of all cars
12 | ASP August 2017
