For 1990-2009 cars

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
A vehicle fails an emission test. The vehicle has an excessive rotten egg smell. Excessive odors do not necessarily indicate excessive emissions.
1 | Were the Important Preliminary Checks performed? | -- | Go to Step 2 | Go to Diagnostic Starting Point - Engine Controls
2 |

1. Run the engine until it reaches operating temperature.
2. Perform an emission test.

Did the vehicle pass the emission test?

--

System OK

Go to Step 3

3 |

1. Connect the scan tool to the data link connector (DLC).
2. Road test the vehicle.
3. Monitor the long term fuel trim memory.

Is the long term fuel trim memory within the value specified?

-20 to +25%

Go to Step 6

Go to Step 4

4 | Is the long term fuel trim memory below the value specified? | -20% | Go to DTC P0171, P0172, P0174, or P0175 | Go to Step 5
5 | Is the long term fuel trim memory above the value specified? | 25% | Go to DTC P0171, P0172, P0174, or P0175 | --
6 |

1. Check for a properly installed fuel cap.
2. Check the fuel system pressure.
3. Perform an injector diagnosis.

Is the problem found?

--

Go to Step 7

Go to Step 8

7 |

1. Repair or replace any fuel system components as needed.
2. Perform an emission test.

Did the vehicle pass the emission test?

--

System OK

--

8 |

1. Inspect the ignition system for proper operation.
2. Inspect the spark plugs for excessive wear, insulation cracks, improper gap, or heavy deposits.
3. Inspect the ignition wires for cracking, hardness, or improper connections.

Is the problem found?

--

Go to Step 9

Go to Step 10

9 |

1. Repair or replace any ignition system components as needed.
2. Perform an emission test.

Did the vehicle pass the emission test?

--

System OK

--

10 |

1. Inspect for vacuum leaks.
2. Inspect the catalytic converter for contamination.
3. Inspect for carbon buildup on the throttle body and the throttle plate and inside the engine. Remove with a top engine cleaner.
4. Inspect the exhaust gas recirculation (EGR) valve for not opening.
5. Inspect for proper positive crankcase ventilation (PCV) operation.

Are all inspections and needed repairs complete?

--

System OK

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