Flow of Diagnosis - Emissions Systems

Flow Of Diagnosis:

This flow of diagnosis is designed to help guide technicians in diagnosing problems related to emission control devices and systems, particularly conditions that may cause an emission test failure. Since this is the starting point for all emissions related diagnostic procedures or finding the cause of an emissions test failure, begin here and follow the flow chart as directed. If the customers complaint is related to driveability and the vehicle has not failed an emission test, refer to COMPUTERS AND CONTROL SYSTEMS.

Numbers below refer to circled numbers in flow chart.

1. Get an accurate description of the complaint and verify. Include filling out the DRIVEABILITY WORKSHEET and VEHICLE REPAIR HISTORY. Refer to INFO TYPE/TECHNICAL MANAGEMENT SUPPORT for forms.
2. Perform Underhood Inspection. A careful visual inspection can often locate the source of a problem without further testing.

a. Check vacuum hoses for splits, kinks, and proper routing.
b. Check ignition wires for cracking, hardness, and proper connections at both the distributor and spark plugs.
c. Check all wiring for proper connections, pinches, and cuts.
d. Check wiring harness for proper routing.
e. Check for missing components.

3. Check for manual updates, testing procedures, warranty and recall information. There may be a factory update that directly addresses the customers complaint.
4. Before trying to diagnose a possible emission control system problem, the computer controls must be verified to be operating properly and any trouble codes present should be addressed first.
5. If there are no trouble codes, refer to Diagnosis by Symptom. for help identifying systems or components that could cause an emission test failure without setting codes.