Definition: The vehicle fails an emission test. The vehicle has an excessive rotten egg smell. (Excessive odors do not necessarily indicate excessive emissions.)

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?

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Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

1. Perform a bulletin search.
2. If you find a bulletin that addresses the symptom, correct the condition as instructed in the bulletin.

Did you find a bulletin that addresses the symptom?

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Go to Step 13

Go to Step 3

Perform the careful visual/physical checks as described at the start of the Symptoms section.

Did you perform the visual/physical check?

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Go to Step 4

Go to Important Preliminary Checks

1. Check for any vacuum leaks. (in the vacuum lines, the intake manifold, the throttle body, etc.).
2. If a problem is present, repair the problem as necessary.

Were any vacuum leaks located?

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Go to Step 13

Go to Step 5

Check the MAP sensor for proper a operation. Refer to Manifold Absolute Pressure Sensor Output Diagnosis .

Was a problem present?

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Go to Step 12

Go to Step 6

1. Check the fuel pressure. Perform the procedure in Fuel System Diagnosis .
2. If a problem is present, repair the problem as necessary.

Was a repair necessary?

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Go to Step 12

Go to Step 7

1. Check the injector connections.
2. If any of the injectors are connected to an incorrect cylinder, correct the problem as necessary.

Was a correction necessary?

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Go to Step 12

Go to Step 8

1. Perform the Fuel Injector Solenoid Coil Test and Fuel Injector Balance Test .
2. If a problem is present, repair the problem as necessary.

Was a repair necessary?

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Go to Step 12

Go to Step 9

1. Check the cooling system for a proper operation.
2. Refer to Engine Cooling for the cooling system diagnosis.
3. If a problem is present, repair the problem as necessary.

Was a repair necessary?

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Go to Step 12

Go to Step 10

1. Check the EVAP canister for fuel loading.
2. If a problem is present, repair the problem as necessary.

Was a repair necessary?

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Go to Step 12

Go to Step 11

Remove any excessive carbon buildup with a top engine cleaner. Refer to the instructions on top of the engine cleaner can.

Is the action complete?

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Go to Step 12

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Reevaluate the vehicle's emissions.

Are the vehicle's emission levels OK?

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Go to Step 19

Go to Step 13

Does the exhaust emission test indicate the excessive CO and HC levels or is the Long Term Fuel Trim significantly in the negative range (Rich condition)?

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Go to Step 14

Go to Step 15

Check the items that can cause the engine to run rich. Refer to DTC P0172 Fuel Trim System Rich for diagnosis. Make any necessary repairs.

Were any repairs necessary?

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Go to Step 12

Go to Step 16

Check the items that can cause the engine to run lean. Refer to DTC P0171 Fuel Trim System Lean for diagnosis. Make any necessary repairs.

Were any repairs necessary?

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Go to Step 12

Go to Step 16

1. Check the catalytic converter for lead contamination.
2. If a problem is present, repair the problem as necessary.

Was a problem found?

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Go to Step 12

Go to Step 17

1. Check for an engine mechanical problem. Perform a cylinder compression check. Refer to Engine Mechanical .
2. If a problem is present, repair the problem as necessary.

Was a repair necessary?

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Go to Step 12

Go to Step 19

1. Check for a fouled Rear Heated Oxygen Sensor and replace the sensor if necessary. Refer to DTC P0138 HO2S Circuit High Voltage Sensor 2 Diagnostic Aids .
2. Replace the Catalytic Converter.

Is the action complete?

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Go to Step 20

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1. Review all of the diagnostic procedures within this table.
2. If all of the procedures have been completed and no malfunctions are present, visually/physically inspect the following items:

•	The scan tool data

•	All of the electrical connections within a suspected circuit and/or system

3. If a problem is present, repair the problem as necessary.

Was a repair necessary?

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Go to Step 20

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Operate the vehicle within the conditions under which the original symptom was observed.

Does the system now operate properly?

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System OK

Go to Step 2