Emission - Enhanced Inspection Maintenance Programs

Group Ref.: Engine Fuel & Emission

Bulletin No.: 436505

Date: April, 1994

SUBJECT:
ENHANCED EMISSION INSPECTION MAINTENANCE PROGRAM-EQUIPMENT REQUIREMENTS

MODELS:
1994 AND PRIOR PASSENGER CARS AND TRUCKS

The intent of this bulletin is twofold; first to inform you of the upcoming Enhanced Inspection Maintenance (I/M) program which will be implemented in specific regions of the country beginning in January 1995 (July 1994 in Maine), and secondly to advise against the purchase of emission related equipment at this time.

This "Enhanced" I/M test (also referred to as the IM240 test) actually consists of three specific tests (and any additional tests individual states may require). They are:

1. The IM24O Test - This test consists of a transient dynamometer test event which will be conducted at centralized (state owned) test facilities. The exhaust gasses measured during the IM240 test event are: HO, CO, and NOx. This test event is much more comprehensive than current I/M tests.

2. The Purge Flow Test - This test measures the flow of unburned hydrocarbons through the purge solenoid during the IM240 test. The objective is to determine that sufficient flow is present under the proper conditions.

3. The Evaporative System Pressure Test - The objective of this test is to evaluate the integrity of the fuel tank vapor recovery system. It is conducted by pressurizing the fuel tank and fuel vapor lines. Pressure is then monitored to assure the system is leak-free.

Currently, there are approximately 30 states which will implement the Enhanced I/M program. In most cases, the test program will be limited to major-urban areas, although some states have elected to implement a statewide program. Check with your local environmental agency to determine if you will be affected by the Enhanced I/M program.

Correction of vehicle failures identified by the Enhanced I/M program will require specialized equipment and diagnostic techniques. General Motors Service Technology Group is developing and validating procedures to diagnose and repair vehicles which fall the new requirements. Our objective is to provide effective repair techniques utilizing proven equipment and to ensure optimal value at the lowest possible cost. Please refrain from purchasing any emission related equipment (i.e. exhaust gas analyzer, dynamometer) until notified by General Motors Service Technology Group to avoid unnecessary expense. Many products currently being marketed are either incapable of performing the required diagnostic and repair functions or include expensive features that may not be required. You will be notified of our findings as information becomes available.