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) provides about 0.45-volt reference to Heated Oxygen Sensor (HO2S). HO2S sensor signal voltage varies from about one volt when exhaust is rich to about 0.1 volt when exhaust is lean. VCM determines if HO2S is functioning properly by reading number of Lean/Rich (L/R) and Rich/Lean (R/L) switches.

Conditions required to set DTC are:

HO2S Diagnostic Enable

No ECT, IAT, MAP, or TP sensor DTCs set.
No EGR or EVAP DTCs set.
No other tests in progress.
No device controls 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 P0132-P0135 are not set.
EVAP purge duty cycle at least zero percent.
Conditions met for greater than 2 seconds.