GM Prizm/Nova 1985-1993 Repair Guide



Component location and vacuum routing diagrams are located at the end of this Section. Please refer to them before beginning any disassembly or testing. Refer to your underhood emission control label for vacuum diagrams not shown. The underhood label often reflects the latest changes made during the production of a vehicle.

There are 3 sources of automotive pollutants; crankcase fumes, exhaust gases, and gasoline evaporation. The pollutants formed from these substances fall into 3 categories: unburned hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx). The equipment used to limit these pollutants is called emission control equipment.

Due to varying state, federal, and provincial regulations, specific emission control equipment may vary by area of sale. The U.S. emission equipment is divided into 2 categories: California and 49 State. In this section, the term California applies only to cars originally built to be sold in California. Some California emissions equipment is not shared with equipment installed on cars built to be sold in the other 49 states. Models built to be sold in Canada also have specific emissions equipment, although in many cases the 49 State and Canadian equipment is the same.

Both carbureted and fuel injected cars require an assortment of systems and devices to control emissions. Newer cars rely more heavily on computer (ECM) management of many of the engine controls. This eliminates the many of the vacuum hoses and linkages around the engine. In the lists that follow, remember that not every component is found on every car.


Fuel Evaporative Control (EVAP)
Carburetor Feedback System
Deceleration Fuel Cutoff
Three-Way Oxidation Catalyst (TWC-OC or TWC)
Cold Mixture Heater (CMH)


Positive Crankcase Ventilation (PCV)
Throttle Positioner (TP)
Exhaust Gas Recirculation (EGR)
Air Suction (AS)
High Altitude Compensation (HAC)
Automatic Hot Air Intake (HAI)
Hot Idle Compensation (HIC)
Automatic Choke
Choke Breaker (CB)
Choker Opener
Auxiliary Accelerator Pump (AAP)
Heat Control Valve