How to diagnose a P0139?

I tried searching the forum but didn't find anything. 2004 Honda CR-V LX 5 speed manual - check engine light recently came on, sometimes it turns off by itself, and sometimes it comes back on. I scanned for codes, and the only code that comes up is P0139 - O2 Sensor Circuit Slow Response (bank 1 sensor 2). Car runs perfectly fine, no drivability issues. I don't want to throw a new o2 sensor at it until I verify that that is the problem. What tests can I do to verify? I have an Equus 3160 scanner that can view live data.

I believe you should get a response from the post cat o2 sensor by introducing propane to the intake.

This is a handle little tool to have for this.

GTC ST05 Oxygen Sensor Tester and Simulator www.amazon.com/dp/B001TCWLO6/ref=cm_sw_r_cp_apa_mV-TzbQA54G9D

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You could do some quick snap throttles and observe sensor voltage change.
Should change within a sec or two of the snap throttle from the normal state.

If no exhaust leaks near sensor then probably sensor not responsive enough.

No other codes?
Fuel trims normal?

The P0139 is a self-test generated by the engine computer as the engine reaches working temperature. The car in running fine because the downstream sensor on the car has not part in the control of the fuel injection. The job of the downstream sensor is simple to check if the cat convertor is doing its job.
It is fairly easy to check if the P0139 is responding using scan data by comparing the output of the upstream sensor (B1SS1) with the downstream sensor (B1S2).
The upstream sensor (B1S1) when the engine is warm continously fluctuates up and down between 0.1v and 0.9v at about 1 full cycle per second the voltage.

The downstream sensor (B1S2) behaves very different when the engine, cat and sensor are warm will look completely different from the upstream. When full warm the voltage output of B1S2 will normally spend most its time either at around 0,9v or 0.1v.
If after a few minutes running you still see it flat lined at 0.5v tthen it it is slam dunk the sensor isn't working, but test the sensor heater circuit before swapping the sensor. If the downstream sensor isn't reading around 0.5v but is up around 0.9v or down at 0.1v then you need to test further.
This is how normal upstrem (Blue) and downstream (green) sensor repond to fluttering throttle pedal to drive the fueling rich and suddenly releasing the throttle to drive the exhaust lean. Fluttering the throttle is simple depressing the throttle about 1/2" on repeatedly for a few seconds to force the exhaust rich, then releasing it to force the exhaust lean. If durring the test you can't force the output voltage high (0.9v=rich) and return quickly low (0.1v = lean) then you have a slow or dead sensor. Again check the sensor heater wiring before swapping the sensor.

This garphic illustrates a normal Upstream and downstream O2 sensor response on a warm engine better.
By working the throttle a small ammount you can force the downstream O2 sensor rich (voltage around 0.9v) then rapidly lifting off and allowing the engine back to normal idle after a few seconds delay the downstream sensor should read lean (around 0.1v) . If by working the throttle you can't force the downstream sensor rich and then lean you a sensor issue.

Good info!

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Thank you, hopefully I'll have some time this weekend to do some troubleshooting. Will report back.