GM Bonneville/Eighty Eight/LeSabre 1986-1999

Catalytic Converter



The catalytic converter is mounted in the engine exhaust stream ahead of the muffler. Its function is to combine carbon monoxide (CO) and hydrocarbons (HC) with oxygen and break down nitrogen oxide (NOx) compounds. These gasses are converted to mostly CO 2 and water. It heats to operating temperature within about 1-2 minutes, depending on ambient and driving conditions and will operate at temperatures up to about 1500°F (816°C). Inside the converter housing is a single or dual bed ceramic monolith, coated with various combinations of platinum, palladium and rhodium.

The catalytic converter is not serviceable. If tests and visual inspection show the converter to be damaged, it must be replaced. There are 2 types of failures: melting or fracturing. The most common failure is melting, resulting from unburned gasoline contacting the monolith, such as when a cylinder does not fire. Usually when the monolith melts, high backpressure results. When it cracks, it begins to break up into small particles that get blown out the tail pipe.

Poor fuel mileage and/or a lack of power can often be traced to a melted or plugged catalytic converter. The damage may be the result of engine malfunction or the use of leaded gasoline in the vehicle. Proper diagnosis for a restricted exhaust system is essential before any components are replaced. The following procedure that can be used to determine if the exhaust system is restricted.


  1. Raise and safely support the vehicle.
  3. Inspect the catalytic converter protector for any damage.

If any part of the protector is dented to the extent that is contacts the converter, replace it.

  1. Check the heat insulator for adequate clearance between the converter and the heat insulator. Repair or replace any damaged components.