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Old 09-05-2010, 03:47 PM
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DaveDees DaveDees is offline
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Join Date: Aug 2008
Location: Chesapeake, VA
Age: 62
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Vehicle: 2010 Jeep Patriot
Trim Level: Latitude
Color: Brilliant Black
Engine: 2003-2008 345ci (5.7L) Hemi V8 345hp 375lb/ft
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From the manual:

P0420-CATALYST 1/1 EFFICIENCY

Diagnostic Test

1. ACTIVE DTC

NOTE: A new rear O2 Sensor along with an aging front O2 Sensor may cause the DTC to set. Review the repair history of the vehicle before continuing.
NOTE: If an O2 Sensor DTC set along with the Catalytic Converter Efficiency DTC diagnose the O2 Sensor DTC(s) before continuing.
NOTE: Check for contaminants that may have damaged the O2 Sensor and Catalytic Converter: contaminated fuel, unapproved silicone, oil and coolant, repair necessary.

Ignition on, engine not running.
With a scan tool, read DTCs.

Is the DTC active at this time?
Yes >> Go To 2
No >> Refer to the INTERMITTENT CONDITION Diagnostic Procedure.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)

2. VISUALLY INSPECT CATALYTIC CONVERTER
Inspect the Catalytic Converter for the following damage.
Damaged Catalytic Converter, dents or holes.
Severe discoloration caused by overheating the Catalytic Converter.
Catalytic Converter broken internally.
Inspect both ends of the converter, inlet and outlet.
Leaking Catalytic Converter.

Were any problems found?
Yes >> Replace the Catalytic Converter. Repair the condition that may have caused the failure.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
No >> Go To 3
9 - 438 ENGINE - ELECTRICAL DIAGNOSTICS DR

3. EXHAUST LEAK
Start the engine.
Inspect the exhaust for leaks between the engine and the 1/1 O2 Sensor.
Inspect the exhaust for leaks between the engine and the 1/2 O2 Sensor.
Turn the ignition off.
If a leak is heard but unable to be located, it may be necessary to use special tool Miller Tool #8404A Evaporative Emissions Leak Detector (EELD) on the exhaust system to find leaks.
Connect the SMOKE supply tip (black hose) to the exhaust cone adapter (if equipped) and place it into the tail pipe.
Set the smoke/air control switch to SMOKE.
Press the remote smoke/air start button.
While still holding the remote smoke/air start button, use the white light (#8404-CLL) to follow the EVAP system path, and look for the source of the leak indicated by exiting smoke.
If a leak is concealed from view, release the remote smoke/air start button, and use the ultraviolet (UV) black light #8404-UVL and the yellow goggles 8404-20 to look for residual traces of dye that is left behind by the smoke.
The exiting smoke deposits a residual fluid that is either bright green or bright yellow in color when viewed with a UV light.
Be sure to check the exhaust manifold to cylinder head connection for leaks.

Are there any exhaust leaks?
Yes >> Repair or replace the leaking exhaust parts as necessary.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
No >> Go To 4

4. ENGINE MECHANICAL
Check the exhaust for excessive smoke caused by an internal problem in the engine.

Is an engine mechanical condition present?
Yes >> Repair the engine mechanical condition as necessary.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
No >> Go To 5

5. AGING O2 SENSOR
A new rear O2 Sensor along with an aging front O2 Sensor may cause the DTC to set.
Review the vehicles repair history.

Has the rear O2 Sensor been replaced without replacing the front O2 Sensor?
Yes >> Replace the Front O2 Sensor as necessary.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
No >> Go To 6

6. CATALYTIC CONVERTER
If there are no possible cause remaining, view repair.
Repair
Replace the Catalytic Converter.

Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
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