2. OBJECTIVES After studying Chapter 24, the reader will be able to:
Prepare for ASE Engine Performance (A8) certification test content area “D” (Emission Control Systems).
Describe the purpose and function of the catalytic converter.
Discuss how the catalytic converter is tested under OBD-II regulations.
Explain the method for diagnosing and testing the catalytic converter.

3. CATALYTIC CONVERTERS
A catalytic converter is an after-treatment device used to reduce exhaust emissions outside of the engine.
This device is installed in the exhaust system between the exhaust manifold and the muffler, and usually is positioned beneath the passenger compartment.
FIGURE 24-1 Typical catalytic converter. The small tube into the side of the converter comes from the air pump. The additional air from the air pump helps oxidize the exhaust into harmless H2O and CO2.

4. CERAMIC MONOLITH CATALYTIC CONVERTER
FIGURE 24-2 A typical catalytic converter with a monolithic substrate.

5. CERAMIC MONOLITH CATALYTIC CONVERTER Catalytic Converter Operation
The converter contains small amounts of rhodium, palladium, and platinum.
These elements act as catalysts.
A catalyst is an element that starts a chemical reaction without becoming a part of, or being consumed in, the process.
In a three-way catalytic converter (TWC), three exhaust emissions (NOX, HC, and CO) are converted to carbon dioxide (CO2) and water (H2O).

6. CERAMIC MONOLITH CATALYTIC CONVERTER Catalytic Converter Operation
FIGURE 24-3 The three-way catalytic converter first separates the NOX into nitrogen and oxygen and then converts the HC and CO into harmless water (H2O) and carbon dioxide (CO2).

7. CERAMIC MONOLITH CATALYTIC CONVERTER Catalytic Converter Operation
FIGURE 24-4 A cutaway of three-way catalytic converter showing the air tube in the center of the reducing and oxidizing section of the converter. Note the small holes in the tube to distribute air from the AIR pump to the oxidizing rear section of the converter.

8. CERAMIC MONOLITH CATALYTIC CONVERTER Converter Light-Off
The catalytic converter does not work when cold and it must be heated to its light-off temperature of close to 500°F (260°C) before it starts working at 50% effectiveness.

9. CERAMIC MONOLITH CATALYTIC CONVERTER Converter Usage
A catalytic converter must be located as close as possible to the exhaust manifold to work effectively.
The farther back the converter is positioned in the exhaust system, the more gases cool before they reach the converter.

10. CATALYTIC CONVERTER WARM-UP TEST
The PCM determines if the catalytic converter is ready for testing based on the following conditions, which may vary by vehicle make, model, and year.
Closed-loop status achieved
IAT sensor temperature higher than 32°F (0°C)
ECT sensor temperature higher than 165°F (18°C)
MAF sensor input from 15 to 32 g/sec
Engine load less than 65% and steady
Engine speed less than 4000 RPM
All of the above conditions met for at least four minutes

11. OBD-II CATALYTIC CONVERTER PERFORMANCE
With OBD-II equipped vehicles, catalytic converter performance is monitored by a heated oxygen (HO2S) sensor both before and after the converter.
FIGURE 24-5 The OBD-II catalytic converter monitor compares the signals of the upstream and downstream O2Ss to determine converter efficiency.

12. OBD-II CATALYTIC CONVERTER PERFORMANCE
FIGURE 24-6 The waveform of an O2S downstream from a properly functioning converter shows little, if any, activity.

13. CONVERTER DAMAGING CONDITIONS
The three main causes of premature converter failure are as follows:
Contamination.
Excessive temperatures.
Improper air-fuel mixtures.
FIGURE 24-7 The highest catalytic converter efficiency occurs when the air-fuel mixture is about 14.7:1.

14. DIAGNOSING CATALYTIC CONVERTERS The Tap Test
The simple tap test involves tapping (not pounding) on the catalytic converter using a rubber mallet.
If the substrate inside the converter is broken, the converter will rattle when hit.
If the converter rattles, a replacement converter is required.
FIGURE 24-8 A catalytic converter that rattles when tapped was removed and the substrate, or what was left of it, fell out. This converter has to be replaced and the root cause of why it failed found and corrected.

15. DIAGNOSING CATALYTIC CONVERTERS Testing Back Pressure with a Vacuum Gauge
A vacuum gauge can be used to measure manifold vacuum at a high idle (2000 to 2500 RPM).
If the exhaust system is restricted, pressure increases in the exhaust system.
This pressure is called back pressure.
Manifold vacuum will drop gradually if the engine is kept at a constant speed if the exhaust is restricted.

16. DIAGNOSING CATALYTIC CONVERTERS Testing Back Pressure with a Pressure Gauge
Exhaust system back pressure can be measured directly by installing a pressure gauge in an exhaust opening.
This can be accomplished in one of the following ways.
To test an oxygen sensor, remove the inside of an old, discarded oxygen sensor and thread in an adapter to convert it to a vacuum or pressure gauge.
To test an exhaust gas recirculation (EGR) valve, remove the EGR valve and fabricate a plate.
To test an air injection reaction (AIR) check valve, remove the check valve from the exhaust tubes leading to the exhaust manifold.
Use a rubber cone with a tube inside to seal against the exhaust tube.
Connect the tube to a pressure gauge.

17. DIAGNOSING CATALYTIC CONVERTERS Testing Back Pressure with a Pressure Gauge
FIGURE 24-9 A back pressure tool can be easily made by attaching a short section of brake line to the shell of an old oxygen sensor. Braze or epoxy the tube to the shell

18. DIAGNOSING CATALYTIC CONVERTERS Testing Back Pressure with a Pressure Gauge
FIGURE A photo of a partially melted catalytic converter that tested okay at idle but had excessive back pressure at idle speeds.

19. DIAGNOSING CATALYTIC CONVERTERS Testing a Catalytic Converter for Temperature Rise
A properly working catalytic converter should be able to reduce NOX exhaust emissions into nitrogen (N) and oxygen (O2) and oxidize unburned hydrocarbon (HC) and carbon monoxide (CO) into harmless carbon dioxide (CO2) and water vapor (H2O).

20. DIAGNOSING CATALYTIC CONVERTERS Testing a Catalytic Converter for Temperature Rise
FIGURE The temperature of the outlet should be at least 10% hotter than the temperature of the inlet. This converter is very efficient. The inlet temperature is 450°F.Ten percent of 450° is 45° (45°450°495°). In other words, the outlet temperature should be at least 495°F for the converter to be considered okay. In this case, the outlet temperature of 525°F is more than the minimum 10% increase in temperature. If the converter is not working at all, the inlet temperature will be hotter than the outlet temperature.

21. DIAGNOSING CATALYTIC CONVERTERS Catalytic Converter Efficiency Tests
The efficiency of a catalytic converter can be determined using an exhaust gas analyzer.
Oxygen level test.
If O2 is zero, go to the snap throttle test.
If O2 is greater than zero, check the CO level.
If CO is greater than zero, the converter is not functioning correctly.
Snap-throttle test.
The O2 reading should not exceed 1.2%; if it does, the converter is not working.
If the O2 rises to 1.2%, the converter may have low efficiency.
If the O2% remains below 1.2%, then the converter is okay.

22. AFTERMARKET CATALYTIC CONVERTERS
FIGURE Whenever replacing a catalytic converter with a universal unit, first measure the distance between the rear brick and the center of the rear oxygen sensor. Be sure that the replacement unit is installed to the same dimension.

23. OBD-II CATALYTIC CONVERTER MONITOR
The catalytic converter monitor of OBD-II uses an upstream and downstream HO2S to test catalytic efficiency.
When the engine combusts a lean air-fuel mixture, higher amounts of oxygen flow through the exhaust into the converter.
The catalyst materials absorb this oxygen for the oxidation process, thereby removing it from the exhaust stream.

24. CATALYTIC CONVERTER REPLACEMENT GUIDELINES
Because a catalytic converter is a major exhaust gas emission control device, the Environmental Protection Agency (EPA) has the following strict guidelines for its replacement.
If a converter is replaced on a vehicle with less than 80,000 mi/eight years, depending on the year of the vehicle, an original-equipment catalytic converter must be used as a replacement.
The replacement converter must be of the same design as the original. If the original had an air pump fitting, so must the replacement.
The old converter must be kept for possible inspection by the authorities for 60 days.
A form must be completed and signed by both the vehicle owner and a representative from the service facility.

25. CATALYTIC CONVERTERRELATED DIAGNOSTIC TROUBLE CODE

26. CATALYTIC CONVERTER OPERATION

27. CATALYTIC CONVERTER OPERATION

28. CATALYTIC CONVERTER OPERATION

29. CATALYTIC CONVERTER OPERATION

30. CATALYTIC CONVERTER OPERATION

31. CATALYTIC CONVERTER OPERATION

32. SUMMARY
A catalytic converter is an aftertreatment device that reduces exhaust emissions outside of the engine.
The honeycomb shape of the catalytic converter is constructed of a ceramic material about in. thick with small square openings.
A catalyst is an element that starts a chemical reaction but is not consumed in the process.
The catalyst materials used in a catalytic converter include rhodium, palladium, and platinum.

33. SUMMARY
A catalytic converter has to be over 500°F (260°C) before it starts to become effective, and is therefore mounted as close as possible to the exhaust parts of the engine.
The OBD-II system monitor compares the relative activity of a rear oxygen sensor to the precatalytic oxygen sensor to determine catalytic converter efficiency.
Catalytic converters can be tested for restriction and for efficiency.

34. REVIEW QUESTIONS
What are the three most commonly used catalysts used in a catalytic converter?
How does a catalytic converter reduce NOX to nitrogen and oxygen?
Why must a catalytic converter be mounted close to the exhaust ports of the engine?
How does the computer monitor catalytic converter performance?
What tests can be performed by a service technician to test the catalytic converter?
What precautions should be adhered to when installing a universal fit catalytic converter?

35. CHAPTER QUIZ
What is applied to the ceramic substrate to make the surface porous?
Honeycomb filler
Washcoat
Aluminum
Cerium

36. CHAPTER QUIZ
What is applied to the ceramic substrate to make the surface porous?
Honeycomb filler
Washcoat
Aluminum
Cerium

37. CHAPTER QUIZ
2. Two technicians are discussing catalytic converters. Technician A says that the exhaust mixture must be at stoictiometric for the best efficiency. Technician B says that the air-fuel mixture must be leaner than 14.7:1 for best performance from a three-way catalytic converter. Which technician is correct?
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B

38. CHAPTER QUIZ
2. Two technicians are discussing catalytic converters. Technician A says that the exhaust mixture must be at stoictiometric for the best efficiency. Technician B says that the air-fuel mixture must be leaner than 14.7:1 for best performance from a three-way catalytic converter. Which technician is correct?
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B

39. CHAPTER QUIZ
3. A catalytic converter has to be at least how hot before it starts to work?
500°F (260°C)
1,000°F (540°C)
1,500°F (815°C)
2,000°F (1,100°C)

40. CHAPTER QUIZ
3. A catalytic converter has to be at least how hot before it starts to work?
500°F (260°C)
1,000°F (540°C)
1,500°F (815°C)
2,000°F (1,100°C)

41. CHAPTER QUIZ
4. What two primary sensors does the PCM use to check the catalytic converter?
Catalytic converter temperature sensor and rear oxygen sensor
Precat and postcat oxygen sensor
Precat oxygen sensor and MAF
MAP and TP

42. CHAPTER QUIZ
4. What two primary sensors does the PCM use to check the catalytic converter?
Catalytic converter temperature sensor and rear oxygen sensor
Precat and postcat oxygen sensor
Precat oxygen sensor and MAF
MAP and TP

43. CHAPTER QUIZ 5. A catalytic converter can be harmed by _____.
Excessive engine oil
Antifreeze
Sulfur from poor-quality fuel
Any of the above

44. CHAPTER QUIZ 5. A catalytic converter can be harmed by _____.
Excessive engine oil
Antifreeze
Sulfur from poor-quality fuel
Any of the above

45. CHAPTER QUIZ
6. Two technicians are discussing testing a catalytic converter. Technician A says that a vacuum gauge can be used and observed to see if the vacuum drops with the engine at idle for 30 seconds. Technician B says that a pressure gauge can be used to check for back pressure. Which technician is correct?
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B

46. CHAPTER QUIZ
6. Two technicians are discussing testing a catalytic converter. Technician A says that a vacuum gauge can be used and observed to see if the vacuum drops with the engine at idle for 30 seconds. Technician B says that a pressure gauge can be used to check for back pressure. Which technician is correct?
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B

47. CHAPTER QUIZ
7. A catalytic converter is being tested with an infrared pyrometer. Which is an acceptable (good converter) result?
The inlet should be hotter than the outlet by 10%.
The outlet should be hotter than the inlet by 10%.
Both the inlet and the outlet should be the same temperature after the converter reaches operating temperature.
The temperature of a catalytic converter is the best test to perform to locate a restricted (clogged) unit.

48. CHAPTER QUIZ
7. A catalytic converter is being tested with an infrared pyrometer. Which is an acceptable (good converter) result?
The inlet should be hotter than the outlet by 10%.
The outlet should be hotter than the inlet by 10%.
Both the inlet and the outlet should be the same temperature after the converter reaches operating temperature.
The temperature of a catalytic converter is the best test to perform to locate a restricted (clogged) unit.

49. CHAPTER QUIZ
8. Which exhaust gas reading indicates a good catalytic converter?
O2 is zero
CO is zero
Both a and b
Neither a nor b

50. CHAPTER QUIZ
8. Which exhaust gas reading indicates a good catalytic converter?
O2 is zero
CO is zero
Both a and b
Neither a nor b

51. CHAPTER QUIZ
9. A P0422 (catalytic converter efficiency failure) is set. What is a possible cause?
Engine mechanical fault
Exhaust leak
Fuel contamination
Any of the above

52. CHAPTER QUIZ
9. A P0422 (catalytic converter efficiency failure) is set. What is a possible cause?
Engine mechanical fault
Exhaust leak
Fuel contamination
Any of the above

53. CHAPTER QUIZ
10. Technician A says that the catalytic converter is warranted for eight years or 80,000 mi, whichever comes first. Technician B says that after replacing the catalytic converter, the old converter must be kept for possible inspection for 60 days. Which technician is correct?
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B

54. CHAPTER QUIZ
10. Technician A says that the catalytic converter is warranted for eight years or 80,000 mi, whichever comes first. Technician B says that after replacing the catalytic converter, the old converter must be kept for possible inspection for 60 days. Which technician is correct?
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B