How do I troubleshoot a downstream O2 sensor control short to power issue

Hello Roy,

Thanks for the quick reply!

I was following that flow chart to step 5 and that is where I measured 12V on terminal A to body ground (I believe terminal A should be 0V?). This was with the O2 sensor unplugged and probing wires on the harness side.

I believe there is a short to power somewhere in the wiring harness but am unsure how to proceed to narrow it down.

Does this make sense? Let me know if I can provide additional information!

- Konrad

Hey Roy,

Thanks for your help, it turns out I was looking at the connections the wrong way.

When I re-measured the voltage from actual A to body ground I got 0-0.1V. My numbers from pin to body ground were:
__
| |
+---+---+
| 0 | 12 |
| 0 | 2.6|
+---+---+

Where the top left is A in the service manual (looking at it from the wiring harnesses perspective as instructed in the manual).

If nothing else appears out of place I am going to replace the sensor.

Thank you for your time and patience!

Konrad

Ahh okok, I did as you told and my measurements were:

+6.2V from one heater circuit pin to sensor ground pin
+1.3V from other heater circuit pin to sensor ground pin
-9V across the 2 heater circuit pins (I don't think the orientation (+/-) matters here?)

Do these values mean anything?

Thanks again for your help!

Konrad

Hello again,

Edit: and some additional info, heater circuit ground to engine block ground is 2.6V, and sensor ground to engine block ground is 17mV.

Something weird is going on.

If I measure from heater circuit + to battery ground I see 12V
If I measure from heater circuit + to sensor ground I see 6V
If I measure from heater circuit + to heater circuit ground I see 9V

Edit: below I did some possibly useless poking around related to the sensor ground:

So there should be a 6V difference between sensor ground and battery ground.

But If I measure from sensor ground to battery ground I see 0V. Does connecting a multimeter (+ to sensor ground, - to battery ground) somehow affect the circuit in ways I don't understand?

If I connect sensor ground to battery ground and force them to have a common ground I can then measure heater circuit to sensor ground at 12V.

It seems like sensor ground is floating somehow. And when the circuit gets connected it goes back to common ground.

It also seems like heater ground is not what it should be.

Edit: I think I am going to try to see if there is continuity between the heater circuit ground and the pin it is supposed to connect to on the control module.

Do you have any ideas? This seems like its above my pay grade :'(.

Thanks again,

Konrad

I used the sensor wire colors to choose what to measure on the body wire harness side, so the wires on the sensor side that I lined up with were:

2 x White wires -> heater circuit (+/-)
Gray wire -> sensor signal
Black wire -> sensor ground

I will go double check the wire colors on the harness side and edit this reply later tonight. I'll add a picture too!

Thanks,

Konrad

Hello again Roy!

Edit: I took it for a highway drive and the check engine light was no longer on. So. Hopefully just a weird condition. I'll come back if the same code triggers again.

Sorry for dropping out of existence for a while, we went on vacation. Here are some pictures with measurements (my assumptions in brackets), let me know what you think:

In the first image you can see:
Grey (sensor signal)
Wire harness side -> brown
Black (sensor signal gnd)
Wire harness side -> white

I measured brown to white and got 0V. I also measured brown to body ground and got 0V.

In the second image you can see:
White (heater power)
Wire harness side -> green
White (heater ground)
Wire harness side -> black/red

I measured green to black/red and got 9.16V. I also measured green to body ground and got 11.85V.

Does this seem normal? I believe according to the service manual's steps I should replace the sensor, but let me know what you think.

Once again thanks for all your help! Really appreciated.

- Konrad