Circuit Description

Powertrain Control Module (PCM) continuously monitors Heated Oxygen Sensor (HO2S) activity for 100 seconds. During the monitor period, PCM counts number of times HO2S switches from rich to lean and from lean to rich. PCM then adds amount of time HO2S took to complete all switches. With this information, an average time for all switches can be determined. If average response time to switch is too slow, DTC will set.

For duplication of DTC, ensure:

• No HO2S 1 heater circuit, EVAP system, misfire, fuel trim, fuel injector circuit, EGR pintle position, TP, IAT, MAP, ECT, CKP or MAF sensor DTCs are set.
• Engine has been running in closed loop fuel control for at least one minute.
• Engine speed is 1000-3000 RPM.
• Engine coolant temperature is greater than 122°F (50°C).
• MAF is 10-30 grams per second.