Diagnostic Aids

WARNING: This page is about a different car, the 2003 Oldsmobile Bravada, 2003 GMC Envoy XL, 2003 GMC Envoy, and 2003 Chevrolet TrailBlazer. However, it is still accessible from the selected car via links, so may be relevant.

Fuel contamination, such as water and alcohol, will affect fuel trim.
System will go rich if injectors are supplying too much fuel.
Using scan tool, review the Failure Records. If an intermittent condition is suspected, see INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.