//bottom ads

GM Astro/Safari 1985-1996 Repair Guide

Evaporative Canister


See Figures 1 and 2

Click image to see an enlarged view

Fig. Fig. 1: Schematic for a typical evaporative emission control system-2.5L engine shown

Click image to see an enlarged view

Fig. Fig. 2: Schematic for a typical evaporative emission control system-4.3L TBI engine shown

To limit gasoline vapor discharge into the atmosphere, this system is designed to trap fuel vapors, which normally escape from the fuel tank and the intake manifold. Vapor arrest is accomplished through the use of the charcoal canister. This canister absorbs fuel vapors and stores them until they can be removed to be burned in the engine. Removal of the vapors from the canister to the engine is accomplished by various means, depending upon the emission systems on your van. For more details about the operation and components of the evaporative emission system, please refer to Emission Controls of this guide.

In addition to the modifications necessary to the fuel system of evaporative emission equipped engines and the addition of a canister, the fuel tank requires a non-vented gas cap. The domed fuel tank positions a vent high enough above the fuel to keep the vent pipe in the vapor at all times. The single vent pipe is routed directly to the canister. From the canister, the vapors are routed to the intake system, where they will be burned during normal combustion.


See Figure 3

Click image to see an enlarged view

Fig. Fig. 3: Periodically check the evaporative canister, lines and fittings for leaks

The only maintenance necessary to this system on most vehicles covered by this guide is a periodic check to make sure the lines and components are intact and still holding (or routing) vapors. Every 30,000 miles (48,000 km) or 24 months, check all fuel, vapor lines and hoses for proper hookup, routing and condition. If equipped, check that the bowl vent and purge valves work properly. Remove the canister and check for cracks or damage, then replace (if necessary). Some early model vehicles will be equipped with a canister that uses a replaceable filter. You should be able to tell by inspecting the bottom of the canister once it is removed for your maintenance inspection. If your canister is equipped, the filter should be visible. Most vehicles covered by this guide use a sealed canister that does not utilize a replaceable filter.


On early model vehicles, the replaceable filter is in the bottom of the carbon canister located in the engine compartment. It should be replaced every 30,000 miles (48,000 km) or 24 months.

  1. Disconnect and mark the charcoal canister vent hoses.
  3. Remove the canister-to-bracket bolt.
  5. Lift the canister from the bracket.
  7. At the bottom of the canister, grasp the filter with your fingers and pull it out.
  9. To install, use a new filter and reverse the removal procedures.