Notes On Intermittents

Engine running, manipulate the oxygen sensor and ECM wiring and connectors while observing ECM Data ED33. If the fault is induced, ED33 will jump below 0.37 volts and the "ECON" status light will go off. Manipulate CKT 413 ground to the engine and look for a loose ground eyelet or ground eyelet installed at wrong location. Check oxygen sensor connector terminals for signs of corrosion or foreign material. Clean if signs of corrosion are evident. If lean engine operation is suspected, perform PFI SYSTEM CHECK  . See TROUBLE SHOOTING - NO CODES article for "Excessive Exhaust Emissions", NOx. An engine that is misfiring may have a lean oxygen sensor indication because of unburned oxygen in the exhaust stream. See TROUBLE SHOOTING - NO CODES article to diagnose the misfiring. If the oxygen sensor circuit appears to be OK, go to PFI CHART A-8: RIGHT O2 SENSOR LEAN  to check for faulty or contaminated sensor.