The bottom left and bottom right are the heater circuit. Testing on the engine harness side, hook the volt meter to ground, and test each wire. One should have 12V and the other should have continuity to ground. Repeat with the test light using battery + on the o2 sensor ground wire, then battery - on the 12V wire.

 

On the vehicle harness side, the bottom right terminal has 12v. The bottom left terminal has infinite resistance to ground...no continuity.

Here's another interesting thing that I discovered...with the meter connected to battery ground on the - lead and connected to the top right terminal (the ground terminal) on the + lead, I'm getting 2volts.

One more strange thing...with the meter connected to the ground terminal (top right) on the - lead, and connected to the bottom right terminal on the + lead, I'm getting 10volts instead of 12v.

When I connect one lead to the top right terminal and the other directly to battery ground, I'm getting perfect continuity, so that top right terminal (harness ground) is connected to ground as it should be, but it seems to be getting voltage as well, since it measures 2volts when checking voltage at that terminal.

When using a test light and connecting to the battery, the top right ground terminal does light up, but it is not quite as bright as it should be, and the test light cuts out just a little, so it seems to be a spotty ground connection. WHen using the test light on the bottom right terminal, it lights up as it should.

By the way, all these tests are with the sensor disconnected, key on, engine not running.

Also, I finally found the engine number after cleaning the area with carb cleaner. Engine # is: F23A4 ...followed by... 4028247

 

#3 and #4 on the picture below are the power and ground for the heater circuit. Don't mess with #1 or #2 as that is for the signal part of the sensor.

The wiring diagram for the primary O2 sensor is confusing me with wire colors. Bottom right has 12V,so the power side is good. You'll need to trace back on bottom left to figure out why you are missing ground. Try to follow that wire harness back to the PCM and look for signs of damage or where that harness might rub against some metal.

I'll try to figure out where this wire grounds. I suspect the PCM, but I'm not sure which pin.

 

PA Honda, did you happen to have any luck finding out where the ground comes from on this bank 1 o2 sensor/heater circuit?

I started to attempt to trace the wires, but it is quite daunting. I may have no choice but to open up the harness, but really hoping to avoid that if at all possible, especially since many separate harnesses join before going to the PCM and it would be a mess to open up. That may be what I end up having to do, but I would definitely like to know for sure that I have an open ground before I go down that road.

Thanks!

 

I think purchasing a shop manual will help you a lot. You can get a pdf of the 98-02 for~$22 at automanualsource.com and is worth the investment.

It looks like the ground side of the circuit grounds at pin B19 on the PCM. You can test at that pin on the PCM to see if the wire has ground at the pcm with the connector still plugged it. Also check that it is the same wire color as at the O2 sensor at pin B19.

 

Hello, I just wanted to report back that buying the correct (and EXPENSIVE) 02 (air/fuel ratio sensor) solved the issue for me completely. I've driven several thousand miles with the $200 Denso sensor (specifically for the ULEV "Ultra Low Emmisions" engine) and no check engine light, so that was the key to solving the issue for me.