For 1990-2009 cars

### Removal Procedure

Notice: The Heated Oxygen Sensors each use a permanently attached pigtail and connector. This pigtail should not be removed from the heated oxygen sensor. Damage or removal of the pigtail or connector could affect proper operation of the heated oxygen sensor.

Important: Take care when handling the Rear Heated Oxygen Sensor 2 (HO2S 2). The in-line electrical connector and louvered end like the O2S 1 must be kept free of grease, dirt or other contaminants. Avoid using cleaning solvents of any type. DO NOT drop or roughly handle the HO2S 2.

1. Turn OFF the ignition switch.

Caution: To avoid any vehicle damage, serious personal injury or death when major components are removed from the vehicle and the vehicle is supported by a hoist, support the vehicle with jack stands at the opposite end from which the components are being removed and strap the vehicle to the hoist.

2. Hoist the vehicle. Refer to Lifting and Jacking the Vehicle in General Information.
3. Disconnect the HO2S 2 electrical connector.

Notice: The use of excessive force may damage the threads in the exhaust manifold/pipe.

4. Carefully remove the HO2S 2.

### Installation Procedure

Important: A special anti-seize compound is used on the HO2S 2 sensor threads. The compound consists of a liquid graphite and glass beads. The graphite will burn away, but the glass beads will remain, making the sensor easier to remove. New or service sensors will already have the compound applied to the threads. If the sensor is removed from the exhaust, and if for any reason it is to be reinstalled, the threads must have an anti-seize compound applied before reinstallation.

1. Coat only the threads of the HO2S 2 with anti-seize compound GM 12377953 or equivalent, if necessary.

Notice: Use the correct fastener in the correct location. Replacement fasteners must be the correct part number for that application. Fasteners requiring replacement or fasteners requiring the use of thread locking compound or sealant are identified in the service procedure. Do not use paints, lubricants, or corrosion inhibitors on fasteners or fastener joint surfaces unless specified. These coatings affect fastener torque and joint clamping force and may damage the fastener. Use the correct tightening sequence and specifications when installing fasteners in order to avoid damage to parts and systems.

2. Install the HO2S 2.

Tighten
Tighten the HO2S 2 to 41 N·m (30 lb ft).

3. Connect the HO2S 2 electrical connector.
4. Lower the vehicle.