Circuit Description

VCM reads Heated Oxygen Sensor (HO2S) activity for 100 seconds. During this period, VCM counts the number of Lean/Rich (L/R) and Rich/Lean (R/L) switches.

With this information, an average time for all transitions can be determined. VCM then divides R/L average by L/R rich average to obtain a ratio. If HO2S ratio is not within range, DTC will set.

Conditions for setting DTC:

• No ECT, EGR, EVAP, IAT, MAP, or TP sensor DTCs set.
• No intrusive tests in progress.
• No active device controls.
• System voltage at least 9 volts.