468 Auto Electricity and Electronics
The oxygen sensor may have a permanently attached
pigtail. Never attempt to remove it. Use a wrench to
unscrew the sensor. Inspect its condition. Some sensors may
be diffi cult to remove at temperatures below 120°F (49°C).
Use care to avoid thread damage. Follow these rules when
replacing an oxygen sensor:
❑
Do not touch the sensor element with anything, such
as water and solvents.
❑
Coat the sensor threads with anti-seize compound
before installation to prevent seizure and damage.
❑
Do not use silicone-based sealers on or around the
exhaust system components. Only use low-volatile
silicone sealers sparingly on engine components. The
PCV system can draw silicone fumes into the engine
intake manifold and over the O2 sensor.
❑
Hand start the sensor to prevent cross threading.
❑
Do not overtighten the O2 sensor. It could be damaged.
❑
Make sure outside vents are clear so that air can circu-
late through the sensor.
❑
Make sure the wiring is reconnected securely to the
sensor.
❑
If the sensor checks out good, check the continuity of
the wiring between the sensor and the computer.
❑
Check the oxygen sensor output and fuel system
operation after installing the sensor.
❑
Repair right away any engine oil leaks that might con-
taminate the new oxygen sensor.
O
2
Sensor Reading
Reading an oxygen sensor can indicate fuel system
problems, silicone contamination, leaded fuel in the tank,
and other troubles, Figure 24-10. To read an oxygen sensor,
inspect the color of the sensor’s tip:
❑
Light gray tip—a normal color for an oxygen sensor.
❑
White sensor tip—might indicate a lean mixture or sili-
cone contamination. Sensor must usually be replaced.
Figure 24-9. OBD II system will let you read oxygen sensor volt-
ages using your scan tool. This is the fastest way of checking the
condition of O2 sensors. (Snap-on Incorporated)
Figure 24-10. Reading an oxygen sensor involves removing and inspecting the color and condition of the sensor. This is similar to
reading spark plugs and may help you fi nd other problems with the engine and computer system. A—New oxygen sensor. B—Rich
mixture from the leaking fuel injector caused black soot buildup on sensor. C—Blown head gasket in the engine caused the sensor
to be contaminated with burned antifreeze. D—Too much silicone sealer on gaskets during engine repair caused this oxygen sensor
contamination. E—Using lead racing fuel ruined this oxygen sensor. F—Oil contamination was caused by a high-mileage engine with
worn piston rings and cylinders.
A B C
D E F