Diagnostic Aids

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Test for fuel contamination. Small amounts of water can be delivered to the fuel injectors and cause a lean exhaust indication. A lean exhaust indication can also be caused by too much alcohol in the fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis (with Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (without Special Tool) .
The system will go lean if an injector is not supplying enough fuel.
A lean condition could be present during high fuel demand due to a fuel pump that does not pump enough fuel.
Review the Failure Records with a scan tool. If an intermittent condition is suspected, refer to Intermittent Conditions .