Test Procedure

HF1 CHECK FOR DIAGNOSTIC TROUBLE CODES (DTCS)

NOTE: Internal deterioration of a catalytic converter is usually caused by abnormal engine operation upstream of the catalyst. Events that can produce higher than normal temperatures in the catalyst are particularly suspect. For example, misfiring can cause higher than normal catalyst operating temperatures.

NOTE: Make sure the customer has not noticed a high engine oil consumption. An engine that consumes oil at a high rate deposits high levels of phosphorus on the catalyst and reduces the catalyst efficiency. Test Procedure

Carry out the PCM self-test.

Are any DTCs present other than P0420?

Yes	No
DISREGARD the current diagnostic trouble code (DTC) at this time. DIAGNOSE the next DTC. GO to DIAGNOSTIC TROUBLE CODE (DTC) CHARTS AND DESCRIPTIONS .	For symptoms without DTCs, GO to HF5. For all others, GO to HF2 .

HF2 CHECK THE HEATED OXYGEN SENSOR (HO2S) WIRING HARNESS AND CONNECTION

Visually inspect the HO2S harness for any indication of crossed wiring.
Visually inspect the HO2S harness for exposed wiring, corrosion, and correct routing.
Visually inspect the PCM connectors for damaged or pushed out pins, corrosion and loose wires.

Are any concerns present?

Yes	No
REPAIR as necessary. Clear the PCM DTCs. REPEAT the self-test.	GO to HF3 .

HF3 CHECK THE FUEL PRESSURE

WARNING: WHEN HANDLING FUEL, ALWAYS OBSERVE FUEL HANDLING PRECAUTIONS AND BE PREPARED IN THE EVENT OF FUEL SPILLAGE. SPILLED FUEL MAY BE IGNITED BY HOT VEHICLE COMPONENTS OR OTHER IGNITION SOURCES. FAILURE TO FOLLOW THESE INSTRUCTIONS MAY RESULT IN SERIOUS PERSONAL INJURY.

Refer to the fuel system WARNING information at the beginning of Pinpoint Test HC. Go To Pinpoint Test HC: Fuel Delivery System .
NOTE: Fuel pressure above specification can produce an abnormally rich air/fuel mixture. This rich air to fuel mixture can cause higher than normal catalyst operating temperatures.
Ignition OFF.
Carry out the fuel system pressure test. Refer to the appropriate Fuel System article for the Fuel System Pressure Test procedure.

Is the fuel pressure between 331 - 485 kPa (48 - 70 psi)?

Yes	No
GO to HF4 .	GO to PINPOINT TEST HC .

HF4 CHECK FOR LEAKS IN THE EXHAUST SYSTEM

NOTE: If a catalyst is in series with a leaking exhaust system, it can fail the catalyst efficiency monitor test.

Inspect the exhaust system for leaks, cracks, loose connections, punctures, or non-factory modifications.

Is a concern present?

Yes	No
REPAIR as necessary. Clear the PCM DTCs. REPEAT the self-test.	GO to HF5 .

HF5 CHECK FOR RESTRICTIONS IN THE EXHAUST SYSTEM

NOTE: A slight pressure in the exhaust system is normal, but excessive exhaust back pressure seriously affects engine operation.

Inspect the following for damage or restrictions:
- front and rear exhaust pipes
- catalytic converter
- muffler and tailpipe assembly

Is a concern present?

Yes	No
REPAIR as necessary. Clear the PCM DTCs. REPEAT the self-test.	GO to HF6 .

HF6 CHECK FOR EXCESSIVE EXHAUST BACK PRESSURE

The internal condition of exhaust system and its ability to flow can be checked with an exhaust back pressure tool.

Is an exhaust back pressure tester available?

Yes	No
GO to HF7.	GO to HF8.

HF7 CHECK FOR EXCESSIVE EXHAUST BACK PRESSURE WITH EXHAUST BACK PRESSURE TOOL

NOTE: Typical exhaust back pressure, when measured near the exhaust manifold and at normal engine operating temperature, should not exceed 20.7 kPa (3 psi) at idle and 55.2 kPa (8 psi) at wide open throttle (WOT) under load.

Install an exhaust back pressure tester and follow the tool manufacturer installation and testing instructions.

Does the exhaust back pressure test indicate a restriction?

Yes	No
REPAIR as necessary. To continue diagnosis of a symptom (lack of power, loss of power, or no start), REFER to ENGINE CONTROLS - SYMPTOM CHARTS (HYBRID) , Symptom Charts. Clear the PCM DTCs. REPEAT the self-test.	No indication of restrictions or leaks has been detected in the exhaust system. To continue diagnosis of a symptom (lack of power, loss of power, or no start), REFER to NO DIAGNOSTIC TROUBLE CODES (DTCS) PRESENT SYMPTOM CHARTS , Symptom Charts. Clear the PCM DTCs. REPEAT the self-test. For all others, GO to HF9.

HF8 CHECK MANIFOLD VACUUM FOR AN INDICATION OF EXCESSIVE EXHAUST SYSTEM RESTRICTION

NOTE: When the engine is first started and is idled, the reading may be normal 51-74 kPa (15-22 in-Hg), but as the engine RPM is increased, the back pressure caused by a clogged exhaust system causes the needle to slowly drop to 0 kPa (0 in-Hg). The needle then may slowly rise. Excessive exhaust restriction causes the needle to drop to a low point even if the engine is only idling.

Attach a vacuum gauge to the intake manifold vacuum source.
Observe the vacuum gauge while increasing the engine RPM.

Does the vacuum gauge indicate an exhaust restriction concern?

Yes	No
REPAIR as necessary. To continue diagnosis of a symptom (lack of power, loss of power, or no start), REFER to ENGINE CONTROLS - SYMPTOM CHARTS (HYBRID) , Symptom Charts. Clear the PCM DTCs. REPEAT the self-test.	No indication of restrictions or leaks have been detected in the exhaust system. To continue diagnosis of a symptom (lack of power, loss of power, or no start), REFER to NO DIAGNOSTIC TROUBLE CODES (DTCS) PRESENT SYMPTOM CHARTS , Symptom Charts. Clear the PCM DTCs. REPEAT the self-test. For all others, GO to HF9 .

HF9 CARRY OUT THE CATALYST MONITOR DRIVE CYCLE

Carry out the catalyst monitor drive cycle. Refer to ON BOARD DIAGNOSTIC (OBD) DRIVE CYCLE .
Carry out the PCM self-test.

Is DTC P0420 present?

Yes	No
INSTALL a new catalyst between the monitored HO2Ss. Do not install a new unmonitored catalyst unless it is repaired as an assembly.	The test is complete and no concerns are present.