Chrysler
Type:
    Powertrain - Fuel and Air Metering - ISO/SAE Controlled
Description:
    HO2S Shorted to Ground Conditions
Cause:
    Key off, engine cool-down period completed, cold engine startup requirement met (ECT sensor input under 100°F), then the test started and the PCM detected that the rear HO2S-12 signal was less than 156 mv prior to starting the HO2S-12 heater test, or that it was less than 156 mv at next engine startup

Generic
Type:
    Powertrain - Fuel and Air Metering - ISO/SAE Controlled
Description:
    O2 Sensor Circuit Low Voltage

GM
Type:
    Powertrain - Fuel and Air Metering - ISO/SAE Controlled
Description:
    HO2S Circuit Low Input Conditions
Cause:
    No PCM codes set, engine running, throttle angle 2-40% for 4.5 minutes and PCM detected the HO2S signal was below 100 mv.