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
1. Go To 2).
No
1. Refer to the INTERMITTENT CONDITION diagnostic procedure.
2. Perform the POWERTRAIN VERIFICATION TEST. (Refer to STANDARD PROCEDURE - POWERTRAIN VERIFICATION TEST) .
2) VISUALLY INSPECT CATALYTIC CONVERTER
Inspect the Catalytic Converter for the following damage.

Damage Catalytic Converter, dents or holes.

Severe discoloration caused by overheating the Catalytic Converter.

Catalytic Converter broke internally.

Leaking Catalytic Converter.

Were any problems found?

Yes
1. Replace the Catalytic Converter. Repair the condition that may have caused the failure.
2. Perform the POWERTRAIN VERIFICATION TEST. (Refer to STANDARD PROCEDURE - POWERTRAIN VERIFICATION TEST) .
No
1. Go To 3).
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.

Are there any exhaust leaks?

Yes
1. Repair or replace the leaking exhaust parts as necessary.
2. Perform the POWERTRAIN VERIFICATION TEST. (Refer to STANDARD PROCEDURE - POWERTRAIN VERIFICATION TEST) .
No
1. Go To 4).
4) ENGINE MECHANICAL CONDITION
Check the exhaust for excessive smoke caused by an internal problem in the engine.

Is an engine mechanical condition present?

Yes
1. Repair the engine mechanical condition as necessary.
2. Perform the POWERTRAIN VERIFICATION TEST. (Refer to STANDARD PROCEDURE - POWERTRAIN VERIFICATION TEST) .
No
1. 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
1. Replace the Front O2 Sensor as necessary.
2. Perform the POWERTRAIN VERIFICATION TEST. (Refer to STANDARD PROCEDURE - POWERTRAIN VERIFICATION TEST) .
No
1. Go To 6).
6) CATALYTIC CONVERTER
If there are no possible cause remaining, view repair.

Repair
1. Replace the Catalytic Converter.
2. Perform the POWERTRAIN VERIFICATION TEST. (Refer to STANDARD PROCEDURE - POWERTRAIN VERIFICATION TEST) .