Repairing Problem Vehicles

The Vehicles:

The Background

Knowing what constitutes a "problem" vehicle is an inexact science. Data analyses showing which vehicles have a higher emissions failure rate and/or excessively high emissions levels can be a first indication. But data analysis lacks a very important element -- the input from the technicians who repair the vehicles. Repair technician input is the critical element to properly identify what constitutes a problem vehicle.

By reviewing requests for technical assistance, questions raised at Tech Nights, and issues discussed frequently during technician training classes, repeated discussions about particular vehicles lead to some consensus on which vehicles are, in fact, problems.

The vast majority of vehicles that fail an I/M 240 emissions inspection can be diagnosed and repaired using existing manufacturer-supplied service information. For the minority of vehicles that are difficult to repair (the "problem" vehicles), there are only a few reasons why the original service information is inadequate:

The effect of high altitude -- At the Front Range's 5,000-6,000 ft. elevation, the air is less dense, effectively changing (richening) the air/fuel mixture, which causes higher emissions of carbon monoxide. Although most cars (since 1984) and trucks (since 1987) were built with automatic altitude compensation, these systems can be prone to failure, and service information/parts availability on altitude compensation is often sparse or nonexistent.
A history of lack of maintenance/vehicle abuse -- Certain vehicle models tend to have been poorly maintained over their useful life. An example is the stripped-down economy model compact car that vehicle owners typically did not bother or could not afford to have serviced regularly.
Lack/availability of adequate information -- While some vehicle manufacturers make any and all service information available to anyone, other manufacturers have historically made very little available outside of their own dealership network. Until very recently, very few service manuals dealt with transient emissions, since most emissions programs used idle testing. An additional factor is cost. A typical manufacturer-supplied service manual for one car model costs over $100. Multiply this by the 150+ models produced each year and service information quickly becomes a major operating expense.
Cost/availability of repair parts -- Auto parts suppliers must live by supply and demand. With the changes in emissions testing and repair across the country, the demand for emissions repair parts is shifting, while the supply side reacts. This results in lack of availability or high costs for certain parts, particularly for older vehicles.

The following 21 make/model/engine combinations have been found difficult to diagnose and repair for emissions failures. The descriptions here are abbreviated, with many vehicles covered by detailed technical bulletins available on request from the Colorado Emissions Technical Centers.

All diagnostic/repair sequences assume:

Reasonable mechanical condition

Manufacturer specified diagnostic and repair sequences have been completed

Vehicles will be operated at a high altitude. (Some of these repairs will cause excessively lean operation at low altitude. Customers should be advised to have their vehicles readjusted if they return to a low altitude.)

A follow-up test drive is required to ensure good drivability in every case.

This information is excerpted/condensed from Report to the General Assembly on Motor Vehicle Emissions Adjustment and Repair, Colorado Air Quality Control Commission, December 1998. Copies of the full report may be obtained from the Air Pollution Control Division, Colorado Department of Public Health & Environment, 303-692-3126.

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For more information, call the Air Care Colorado Hotline at 303-456-7090. Se habla Español. Site updated 1/31/09.