Diagnostic Aids

To locate an intermittent problem, use scan tool to monitor HO2S21 lambda value with ignition on, engine off. Wiggling wires while watching for a change in HO2S21 lambda value may locate area where an open, short to ground or short to voltage in wiring may exist.

A short to ground or a short to voltage on any HO2S non-heater circuit will display 3.999 for HO2S21 lambda value on scan tool. An open input pump current or reference ground circuit will display 1.000 for HO2S21 lambda value on scan tool.

An open, short to ground or short to voltage on HO2S21 circuit may cause engine to misfire on cylinders No. 2, 4 and 6.