Basic EVAP Functions

The M96.5 and later TRIONIC EVAP systems retain all of the components and basic functions of our earlier evaporative emissions systems. The following is a quick review of the hardware and concepts involved.

EVAP Canister

Unlike the charcoal canister used on 9000 and older 900 models, the M96.5 and later EVAP canister is of a completely sealed design. The three nipples on the top of the canister are the only way vapor or purge air should be able to enter or leave the canister. Flow from any other source, such as a small crack in the housing or poor glue joint, will set a fault code.

EVAP Valve

Like all other OBD II EVAP valves, the 900 M96.5 and later TRIONIC valve is NORMALLY CLOSED unless it is being provided with power from the main relay and a pulsing ground by the TRIONIC ECM. The ECM will not begin to operate the EVAP valve until the coolant temperature is above 140°F (60°C) and the system is in closed loop. When purging, the EVAP valve will normally be active for 4.5 minutes, cycle off for 30 seconds, run for 4.5 minutes, off for 30 seconds and so on. The most practical way to tell that the EVAP valve is actively purging is simply to grab it. You can feel it pulse much more readily than you can hear it.

Filler Cap

All M96 and later 900s use a special OBD II filler cap (black top, white body) which includes a relief valve to prevent collapsing the fuel tank if a failure in another part of the system results in excessive vacuum. Like all earlier filler caps, it must be tightened down THREE CLICKS to insure a tight seal to the filler neck.

Filler Neck/Roll-Over Valve

The M96.5 and later fuel filler neck has been modified to include a mounting point for the tank pressure sensor which forms the heart of the enhanced EVAP system. This sensor picks up tank pressure through a short hose which connects to a nipple molded into the top of the filler pipe. The vent line running forward to the EVAP canister connects to the roll-over valve which is an integral part of the filler pipe. The roll-over valve is a simple, gravity activated, device which normally is quite trouble free. The vent line connection is accessible through the right rear wheel well.

Throttle Housing Vacuum Port

The purge line from the EVAP valve slips over a metal nipple which is glued into the throttle housing. It is not a common problem, but don't overlook the possibility of a blockage or restriction in this nipple.