Heated Oxygen Sensors

WARNING: This page is about a different car, the 2003 Pontiac Grand Am, 2003 Oldsmobile Alero, 2003 Chevrolet Monte Carlo, and 2003 Chevrolet Impala. However, it is still accessible from the selected car via links, so may be relevant.

CAUTION: DO NOT attempt to measure oxygen sensor output voltage using a conventional voltmeter. Current drain of voltmeter could damage sensor. Oxygen sensor voltage signal can be measured using a 10-megohm (minimum input impedance) digital voltmeter.

Heated Oxygen Sensors (HO2S) 1 and 2 are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the vehicle is first started, the Powertrain Control Module (PCM) operates in an Open Loop mode, ignoring the HO2S signal voltage when calculating the air-to-fuel ratio. The PCM supplies the HO2S with a reference, or bias, voltage of about 450 mV. The HO2S generates a voltage within a range of 0-1000 mV that fluctuates above and below bias voltage once in Closed Loop. A high HO2S voltage output indicates a rich fuel mixture. A low HO2S voltage output indicates a lean mixture. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature, and to provide an accurate voltage signal. If the PCM detects that the HO2S 1 voltage remains above or below a calibrated amount for an excessive amount of time, a related DTC will set.

The HO2S 1 has the following circuits:

A HO2S 1 high signal circuit.
A HO2S 1 low reference circuit.
A HO2S 1 heater ignition voltage circuit.
A HO2S 1 heater low control circuit.
A low reference loop circuit.

The HO2S 2 has the following circuits:

A HO2S 2 high signal circuit.
A HO2S 2 low signal circuit.
A HO2S 2 heater ignition voltage circuit.
A HO2S 2 heater ground circuit.

If the HO2S pigtail wiring, connector, or terminal are damaged, replace the entire HO2S assembly. Do not attempt to repair the wiring, connector, or terminals. For the sensor to function properly, the sensor must have a clean air reference. This clean air reference is obtained by the HO2S wires. Any attempt to repair the wires, the connectors, or the terminals could result in the obstruction of the air reference. Any attempt to repair the wires, the connectors, or the terminals could degrade oxygen sensor performance.

To control emissions of Hydrocarbons (HC), Carbon Monoxide (CO), and Oxides Of Nitrogen (NOx), the system uses a 3-way catalytic converter. The catalyst within the converter promotes a chemical reaction which oxidizes the HC and CO present in the exhaust gas, converting the HC and the CO into harmless water vapor and carbon dioxide. The catalyst also reduces NOx, converting the NOx into nitrogen.