Circuit Description

WARNING: This page is about a different car, the 2000 Isuzu Hombre. However, it is still accessible from the selected car via links, so may be relevant.

Vehicle Control Module (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 preset range, DTC will set.

Conditions required to set DTC are:

HO2S Diagnostic Enable

No ECT, IAT, MAF, MAP, or TP sensor DTCs set.
No EVAP DTCs set.
No device controls are active.
No intrusive tests are active.
System voltage is 9 volts or greater.

Response Test Enable

Operating in closed loop.
Closed loop low MAP not active.
ECT is 134°F (57°C).
Engine run time is greater than 75 seconds.
Engine speed is 1100-3000 RPM.
MAF is 15-55 grams per second.
DTCs P0131, P0132, P0134 and P0135 are not set.
EVAP canister purge duty cycle at least zero percent.
Conditions met for greater than 2 seconds.