DTC P0138: HEATED OXYGEN SENSOR NO. 2 CIRCUIT - HIGH VOLTAGE Chevrolet Venture I

Note. For circuit reference, see WIRING DIAGRAMS article.

Circuit Description

The Heated Oxygen Sensor 2 (HO2S 2), located at rear of catalytic converter, produces an output signal relative to oxygen storage capacity of catalytic converter. HO2S 2 signal is less active than signal produced by front oxygen sensor. If HO2S 2 signal voltage remains excessively high for an extended period of time, DTC P0138 will set.

For duplication of DTC, ensure

1. No active misfire, fuel injector circuit, TP sensor, EVAP, IAT sensor, MAP sensor, fuel trim, EGR, ECT sensor, MAF sensor or CKP sensor DTCs are set.
2. Engine coolant temperature is greater than 149°F (65°C).
3. TP sensor angle is 3-40 percent.
4. Closed loop commanded air/fuel ratio is 14.5-14.8:1.
5. HO2S 2 signal voltage remains greater than 999 mV during normal closed loop operation, or greater than 200 mV during deceleration fuel mode operation.