DTC P1134 & P1154: Ho2S Transition Time Ratio - Bank 1 & 2, Sensor 1: Description

WARNING: This page is about a different car, the 2001 GMC Savana, 2001 Chevrolet RV Cutaway, 2001 Chevrolet Cutaway, and 2001 Chevrolet Chevy Express. However, it is still accessible from the selected car via links, so may be relevant.

Heated Oxygen Sensor (HO2S) is a sensor designed to create a voltage relative to oxygen content in engine exhaust stream. Powertrain Control Module (PCM) supplies HO2S with a signal high and low circuits. Ignition voltage and ground are supplied to HO2S heater by independent circuits. Oxygen content of exhaust indicates when engine is operating lean or rich. When HO2S detects that engine is operating rich, signal voltage is high, and decreases signal voltage as engine runs leaner. This oscillation more than and less than bias voltage, sometimes referred to as activity or switching, can be monitored with HO2S signal voltage. HO2S contains a heater that is necessary to quickly warm sensor to operating temperature. Heater also maintains operating temperature during extended idle conditions. HO2S needs to be at a high temperature to produce a voltage. When HO2S reaches operating temperature, control module monitors HO2S bias, or reference, voltage. PCM also monitors HO2S signal voltage for closed loop fuel control. During normal closed loop fuel control operation, PCM will add fuel, or enrich mixture, when HO2S detects a lean exhaust content. PCM will subtract fuel, or "lean out" mixture, when HO2S detects a rich exhaust condition. This DTC determines if difference in transition times from lean-to-rich or rich-to-lean has exceeded a maximum ratio. PCM monitors time needed for HO2S to transition from more than 600 millivolts to less than 300 millivolts and vice versa. DTC P1134 or P1154 will set if either of these times is longer than the other by a calibrated ratio.