Diagnostic Aids

Check for HO2S wires grounding against exhaust manifold. Oxygen supply inside HO2S is necessary for proper operation. This supply of oxygen is provided through HO2S wires. Inspect all wires and terminals for breaks or contamination.

Check for rich fuel injector(s) or excessively high fuel pressure. Perform injector balance test. See appropriate SYSTEM & COMPONENT TESTING article. Check for saturated EVAP canister or incorrectly installed MAF sensor. Disconnect MAF sensor and observe if rich condition is corrected. Check for leaking fuel pressure regulator or leaking regulator vacuum hose. Check TP sensor. An intermittent TP sensor output will cause system to go rich.