 O2 Sensor Identification Guide An OBD Scan Tool will usually identify Oxygen Sensors by the Bank Number (B1 = Bank 1) and Sensor Number (S1 = Sensor 1). Bank 1 will always contain Cylinder 1, which is located closest to the front of the engine.
Part manufacturers often use different terms than scan tools to identify sensor positions. Regardless of the vehicle's engine orientation, the right or left bank is determined by viewing the engine from the rear (opposite the drive belts).
A Upstream Sensor (Before Converter)
B Downstream Sensor (After Converter)
C Left or Front Upstream Sensor (Before Converter)
D Right or Rear Upstream Sensor (Before Converter)
 Common O2 Sensor Contaminants Oxygen (O2) Sensors commonly fail due to contamination. When checking or replacing an O2 Sensor, visually inspect the sensor body to determine if it has been contaminated by a faulty part or substance upstream, and correct the fault before replacing the sensor.
| ANTIFREEZE POISONING |
Common Causes:
- Cracked or warped cylinder head
- Leaking cylinder head gasket
- Leaking intake manifold gasket
 Antifreeze Poisoned O2 Sensor |
| SILICONE POISONING |
Common Causes:
- Use of an improper silicone gasket sealant on the engine
 Silicone Poisoned O2 Sensor |
| CARBON BUILDUP |
Common Causes:
- Clogged air filter
- Leaking or defective fuel injector
 Carbon Buildup O2 Sensor |
|
