Oxygen Sensor Contaminants

CARBON
Black carbon or soot deposits result from over-rich mixtures. However, carbon does not harm a Heated Oxygen Sensor (HO2S). Deposits can be burned off in the engine by running it at least part throttle for two minutes.

SILICA CONTAMINATION SOURCES
RTV
Certain RTV silicone gasket materials give off vapors that contaminate the oxygen sensor. The sand-like silica particles from the RTV silicone embed in the molecules of the sensor element and plug up the surface. This results in "lazy" HO2S response and engine control. The sensor will also have a white-like appearance.

Fuel
There is also a possibility of silica contamination caused by silicone in the fuel. Careless fuel handling practices with the transport containers can result in unacceptable concentrations of silicone in the fuel at the pump.

Lubricants
There is also a possibility of silica contamination caused by silicone in lubricants used to install vacuum hoses on fittings.

LEAD
Lead glazes sensors. It can be introduced when regular, or leaded fuel, is burned. It is difficult to detect lead contamination by visual inspection.

OTHER SUBSTANCES
Oil deposits will ultimately prevent sensor operation. The sensor will have a dark brown appearance. Causes of high oil consumption should be checked. The additives in ethylene glycol can also affect sensor performance.

This produces a white-like appearance. If antifreeze enters the exhaust system, you will likely encounter other, more obvious, symptoms of cooling system trouble.

MULTIPLE FAILURES
If you encounter multiple or repeat HO2S failures on the same vehicle, consider contamination.

Leaded fuel, silica contamination from uncured, low-grade (unapproved) RTV sealant, and high oil consumption are possible.

DIAGNOSTIC TROUBLE CODES (DTC)s
A problem in the HO2S circuit or fuel system should set the following DTC(s) for the indicated condition:

Open Circuit
Code 13 Bank 1 (Left) Heated Oxygen Sensor Circuit. DTC 13
OR
Code 63 Right (Bank 2) Open Oxygen Sensor Circuit. Powertrain Controls - ECM/PCM

Lean Indication
Code 44 Left (Bank 1) Oxygen Sensor Circuit (Lean exhaust). Powertrain Controls - ECM/PCM
OR
Code 64 Right (Bank 2) Oxygen Sensor Circuit (Lean Exhaust). Powertrain Controls - ECM/PCM

Rich Indication
Code 45 Left (Bank 1) Oxygen Sensor Circuit (Rich Exhaust). Powertrain Controls - ECM/PCM
OR
Code 65 Right (Bank 2) Oxygen Sensor Circuit (Rich Exhaust). Powertrain Controls - ECM/PCM

Refer to applicable DTC chart if any of the above DTCs were stored in memory.