Test purpose:
This test is designed to help you identify if the O2 sensors (lambda sensors) are
operating correctly. Because O2 sensors are measuring oxygen levels in engine
exhaust they are exposed to high heat and depending the manufacturer they can be
in areas that can be damaged by road debris. Faulty O2 Sensors can cause poor
engine performance, high exhaust emissions and high fuel consumption. O2
Sensors typically output a voltage in reference to the lean and rich state of the fuel
mixture (higher or lower oxygen levels) in the exhaust and will generate a voltage
between .1V and .9V (for upstream O2 sensors) as the engine fuel air mixture
alternates between rich and lean. If the upstream O2 sensor and emissions control
system are doing their job correctly, the downstream O2 sensor should stay at
approximately .45V as it is past the catalytic converter. This test will allow you to
monitor the output of the O2 sensor voltage in a graphed view to either see the
alternation of rich to lean states or the post catalytic converter leveled oxygen level.
Tool Setup
• Top Chanel: N/A
• Bottom Channel: Voltage DC - Auto Ranged
• Speed: 64MS (256) or (4000 Hz 256 SMPL)
Test Procedures:
• Place Leads on tool to Volts DC and Common
• Use Probe Tips on leads or clamps
• Connect the positive probe tip or clamp to the positive output of the 02
sensor
• Connector the ground probe tip or clamp to the ground of the 02 Sensor
• Set the Meter Mode to Graph
• Turn over engine and set revs to 2500 RPM
• Upstream O2 Sensor: Watch the characteristics of the reading to change
from .1V - .9V
• Downstream 02 Sensor: watch the characteristics of the reading stabilize to
approx. .45V to .5V (450 mV to 500mV)