Snap Throttle Test of Upstream Sensors Using Bear Analyzer

SNAP THROTTLE TEST OF UPSTREAM SENSORS USING BEAR ANALYZER "UNISCOPE"

NOTE:
If pinging is encountered while performing the Snap Throttle Test, poor fuel quality is usually the cause. This must be remedied before proceeding with test.





1. Calibrate lead set for accurate voltage readings.

2. Switch off A/C compressor.

3. Set Uniscope red channel on +/- 7 VDC and 32 ms.

4. Back probe pin 33 of red 36 pin connector for bank B, or pin 34 for bank A sensors.

5. Run engine to operating temperature (approx. 195°F) then heat engine and H02S's fully by running engine 2-3 minutes at 2500 rpm. Let idle for 5 seconds but no more than 20 seconds.

6. Push record on Uniscope.

7. Rev the engine rapidly four to five times in 2 second intervals from idle to wide open throttle (do not exceed 300 rpm).

8. Examine recording frame by frame, set cursor # 1 at maximum HO2S voltage and take a reading; record maximum voltage results. Set cursor # 2 on minimum HO2S voltage and record results.

9. Measure rich-lean response times.

NOTE:
Do not judge response times at the beginning of the record cycle (i.e. frames 1-3).

10. Print screens using print icon on upper right corner of screen.





The chart will give a graphic depiction of the sensor response and voltages in relation to the setting of P-codes. Note that the response time is measured between two thresholds. The lean voltage threshold is 3.3 V; the rich is 1.3 V. Set cursors at these two voltages to measure response time.





It is important to note that the fault limits for response time exceeds the typical response observed during a snap throttle test; the higher limits are used by the ECM to flag codes under normal, not snap throttle driving conditions. The decision to condemn sensors should be based on the chart above.

If there is any doubt about the visual readings from the wave forms, or if exact test results are desired, use the Uniscope cursors to measure the maximum voltage, minimum voltage, and response time. Most faulty HO2S will be obvious from a visual inspection of the wave forms. Below are some examples of wave forms.





In this example the rich to lean response time is 124.2 ms. This response time exceeds the 100 ms limit, therefore the sensor should be replaced. Note that the voltages specified vary somewhat from the published thresholds. This is due to the difficulty of setting the cursors precisely with this set-up; for the purpose of this test, it is close enough.





In this example, the lean to rich response time is 36.0 ms; well within the specifications of 125.0 ms using the snap throttle test.