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OXYGEN
2-23
8) Observe RICH/LEAN lights during fast idle.
• The TEST light column also indicates sensor voltage,
but it is easier to check operation by watching the RICH/
LEAN lights.)
• Maintain throttle partially open (2000 RPM idle).
– IF the RICH/LEAN lights flash back and forth every 3
seconds or less...
THEN the sensor is good and no further testing is
necessary. Go to step 10.
– IF it takes longer than 3 seconds for the RICH/LEAN
lights to switch back and forth...
THEN the sensor may be degraded. Go to step 10,
then do the Off-Car test on page 2-24
– IF the RICH/LEAN lights do not flash back and forth...
THEN go to step 9.
9) Observe RICH / LEAN lights during throttle changes.
• Quickly move throttle from idle to partially open (2000
RPM) position then back to idle. (This attempts to create
a momentary rich or lean engine operating condition.)
Repeat this throttle action several times while observing
the RICH/LEAN lights.
– IF the RICH/LEAN lights switch within 3 seconds of the
throttle action...
THEN the sensor is good and no further testing is
necessary. Go to step 10.
– IF it takes longer than 3 seconds for the RICH/LEAN
lights to switch...
THEN the sensor may be degraded. Go to step 10. Do
the Off-Car test on page 2-24
– IF the RICH/LEAN lights do not flash back and forth...
THEN go to step 10. Do the Off-Car test on page 2-24.
10) On-Car test is complete - Turn ignition key OFF.
• Set RANGE switch to POWER OFF and remove all test
leads.
• If the RICH / LEAN lights did not flash, or flashed
too slowly, in steps 8 or 9, then do the Off-Car test
on page 2-24.
RICH
LEAN
RICH
LEAN