See Figure 1
There are two different types of catalytic converters used on Volvos: the oxidation type converter and the three-way converter.
All 1975-76 Volvos manufactured for California, 1975 164 models with manual transmission and overdrive for the 49 states, 1977 49 states 240 series and all 1977 260 series, all 1978 49 states models (except some 242 DL, 242 GT and 262 C models), and all 1979 49 states 240 series models, except the 242 GT, are equipped with the oxidation type converter. The converters are installed in these vehicles to further control emissions of carbon monoxide and hydrocarbons which have resisted the treatment of the air injection system.
The converter is installed in the exhaust system ahead of the muffler. The converter uses platinum and palladium in a substrate or beaded form as the catalyst. The catalyst and the oxygen supplied by the air pump then react with the exhaust gases producing harmless carbon dioxide and water vapor, as well as a minute amount of sulphur dioxide and sulfuric acid.
The converter is designed to last 50,000 miles (80,515 km), as long as leaded gasoline is not used. Since lead is not normally present in today's gasoline, the possibility of lead-related converter damage is remote. However, in the event that leaded gasoline or a lead additive is used, such lead will coat the catalytic substrate or beads, preventing the reaction process and rendering the converter ineffective.
At 15,000 mile (24,155 km) intervals, the retaining bolts for the converter must be checked for tightness. A service reminder light on the dashboard lights at 15,000 mile (24,155 km) intervals. To extinguish the light, press the white reset button at the rear of the odometer.
The 1977 California 240 series, all 1978-80 260 California series, all 1979 49 states 260 series, all 1980 and later (except diesel) models, and the 1979 49 states 242 GT are equipped with three-way catalytic converters.
The purpose of the three-way catalytic converter is to neutralize carbon monoxide, hydrocarbons and oxides of nitrogen in the exhaust gases. The main difference between this converter and the oxidation converter is that the three-way converter is able to process large amounts of oxides of nitrogen (NOx), while the oxidation catalyst cannot.
The operating range of the three-way catalyst is limited to a narrow band around the ideal air/fuel mixture for the engine (14.7:1). To keep the mixture within this narrow band, an oxygen sensor is used to monitor the amount of oxygen in the exhaust gases. The readings from the oxygen sensor are transmitted to the ECU (Emissions control unit or fuel injection computer) which fine tunes the air/fuel mixture being delivered into the engine. Refer to the following Oxygen Sensor Feedback System (Lambda Sond) coverage for more information on the oxygen sensor system.
As with the oxidation catalytic converter, the use of leaded fuel or fuel additives in the engine will render the three-way catalyst ineffective. Extremely high temperatures within the catalyst will impair or even melt the ceramic insert inside the converter.