Initial Inspection and Diagnostic Overview
INSPECTION AND VERIFICATION1. Verify the customer concern by running the engine at 2000 rpm's or by road testing the vehicle, and that the vehicle:
- Contains dual Three Way Catalytic Converters (TWCs).
- Has two upstream Heated Oxygen Sensors (HO2S) mounted before the TWCs and two downstream Catalyst Monitor Sensor (CMS) mounted after the Three Way Catalytic Converters (TWCs).
2. Visually inspect the components of the exhaust system and related controls that may affect exhaust gas quality or cause backfire or loss of power.
3. Visually inspect for obvious signs of mechanical and electrical damage; refer to the following chart:
VISUAL INSPECTION CHART
4. Exercise the wiring and connectors of the components for obvious problems due to looseness, corrosion, or other damage.
NOTE: This must be done while the engine is fully warmed and the system controls are activated.
5. Check the vacuum lines and connections for looseness, pinching, leakage, splitting, blockage, or other damage.
6. If a vacuum line or orifice (restrictor) blockage is suspected, correct the cause before proceeding to the next step.
7. If the fault is not visually evident, determine the symptom and proceed to the Symptom Chart.