So Fix it

A catalytic converter is an exhaust component that was put on all production cars since 1974. The job of a catalytic converter on a Pontiac Grand Prix is to burn up any left over gas that went through the engine and was left unburned. The catalytic converter uses a chemical reaction to change the unburned engine gases to less toxic gases, like carbon dioxide and water vapor. This helps cut down on the pollutants emitted, from the Grand Prix, into the atmosphere.

General Location

Because the catalytic converter is an exhaust component, it is located in the exhaust system on the underside of the Grand Prix. On the Grand Prix, the exhaust system attaches to the engine block and to the underside of the car using brackets, and then exists out the rear of the vehicle with dual exhaust tips. The converter looks like a small muffler, or rectangular box, around the middle of the exhaust pipe. The primary components of the converter are usually made out of stainless steel.

Location on the Exhaust

The catalytic converter is located between the exhaust manifold and the muffler. The exhaust manifold is a pipe that moves the engine gasses from the engines combustion chamber into the exhaust system. The muffler is a large chamber located near the end of your exhaust system that reduces the noise energy of the exhaust gasses as they exit the exhaust system.

Why Its on the Car

Toxic gasses are released when the engine in the Grand Prix runs. These gasses could cause depletion of the ozone, as well as illness or damage to the environment, if they were released without being broken down into less harmful gasses. Because the government put emission restrictions into place to slow the buildup of pollution, all cars were equipped with catalytic converters after 1974. This has cut down on the pollution being released by automobiles significantly since the government required all cars to have the converter.

Why Its in the Exhaust System

The exhaust system on the Grand Prix, just like every other car, is used to move gas from the engine out to the surrounding air. The converter is located after the exhaust manifold so that it can take the toxic engine gasses and convert them into less toxic ones before the exhaust moves into the muffler and eventually exist the rear of the Grand Prix. Without the catalytic converter within the exhaust system, exhausted toxic gases from the engine would be released into the atmosphere, causing toxic buildup.

The throttle position sensor, or TPS, monitors the position of the throttle. The TPS is a potentiometer that sends an electrical signal to the powertrain control module. The PCM uses this information to adjust fuel/air mixtures. A faulty TPS will cause erratic idling since it sends the wrong information to the PCM.

Finding the TPS

The TPS is located on the end of the throttle shaft on the throttle body. To find the throttle body look to the left of the intake cover. The intake cover has the name of the engine on it, for instance it may read "3400 SFI" in large letters. The throttle body is just to the left of the cover and close to the firewall. The TPS is a small black electrical unit mounted right beside the air intake duct.

Function of the TPS

The TPS sends different voltages to the PCM depending on the angle of the throttle valve. If the TPS is broken or loose it may cause erratic idling since the PCM is receiving different voltages, as if the throttle were moving.

Checking the TPS

You can check the TPS by first checking that the electrical connections are tight and not corroded. Check the wiring harness and wires for damage or breaks. Use a voltmeter to test the current coming from the TPS. With the engine off the TPS should be sending 5.0 volts of current. Check the current at idle and increasing RPMs. At idle the voltage should read 0.5 volts and at high rpm it should read 4.5 volts.