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. HO2S produces no voltage and acts as an open circuit when temperature is less than 680°F (360°C). VCM determines if HO2S is functioning properly by reading number of Lean/Rich (L/R) and Rich/Lean (R/L) switches. VCM will set DTC if HO2S is slow to respond to changes in exhaust oxygen content.

Conditions required to set DTC are:

HO2S Diagnostic Enable

L/R and R/L switches less than 20 counts within 100 seconds.
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.