When I had that car mine wasn't a ULEV model, so I didn't have that A/F sensor relay. I think it's to provide power to the heater in the sensor, but I don't know where it's located.

 

Page 22-9 shows the location of the relay.

You should do some testing of the wiring while everything is plugged in. An unplugged connector can read 12V on the volt meter, but deliver a lot less voltage when under load. Search youtube videos for voltage drop testing.

I would start by testing for 12V to the heater circuit of your O2 sensor by backprobing the electrical connector.

 

Found the relays, tested them (tested good) and then swapped them. Same result.

Thanks, I'm familiar with voltage drop through my education and work. When I replaced the heater element with a light bulb (used the old sensor and cut the wires) it was very bright and drew about an amp. The post I read said it would flicker quickly and it did. The brightness indicated a high voltage under a pretty good load. Then I placed a 10 ohm resistor in series the light and it was very dim. The 1167 code was generated with both of those test. Heat element resistance for a ULEV is between 2 and 20 ohms. I will measure the voltage to verify it's ~12VDC.

I just reran the DTC P1167 diagnostic test on page 11-83, all checks out fine. I will run the P1166 test tomorrow.

I truly am baffled by this problem.

 

Glad you know the electrical tests, because most people can miss/skip an important test by doing tests on an unplugged circuit.

Based on your test with the bulb, you are getting current through that circuit with a good ground.

This may seem like an obvious question. Seems like we are missing something. Did you replace the sensor in the catalytic converter, or on the bottom of the exhaust manifold (or on the pipe out of the exhaust manifold connecting to the catalytic converter)?

What was the part number for the PCM you purchased for this car?

 

I agree, it seems like I/we are missing something. Both the upstream and downstream sensors have been replaced. Currently, only the upstream A/F ratio sensor has my attention, the one in the exhaust manifold nearest the engine, under the hood. The part number is a Denso 234-9014. The downstream sensor, in the catalytic converter, was replaced with a Denso 234-4621 O2 sensor.

The used PCM part number I purchased is 37820-PAA-L21. This matched the original part number exactly.

Please ask any questions, obvious or not. Maybe it will help me think of something else to try. I will verify the downstream O2 sensor part number on the device and test its heater voltage.

 

Did this vehicle always have these codes since you owned it? Or is this a recently purchased car?

The 98-02 accords get confusing with UL, ULEV, SULEV, California emissions, so I am not sure if I looked at the right version of your car.

Go to hondapartsnow.com and use your VIN to identify your vehicle. Under electrical, control unit - cabin, look up the OEM part number for the PCM for your car.

 

I've owned the car for 10 years. Bought it with 110K and it now has 202K. The codes have only been ON for 2 months.

The engine was replaced 6 months after I purchased it. The replacement engine is also an ULEV 4 cylinder.

hondapartsnow.com has the PCM listed as 37820-PAA-L23 and I have an -L21. The PCM in the car '-L21' has worked correctly for 10 years.

 

One thing I was just reminded of, the cruise control does not work in the car. It used to work, my son doesn't use it and when I last drove the car due to the CEL, it wasn't working. May have happened around the same time but not sure. The indicators come on like it's working but nothing happens.

The test for P1167 passed without issue. Should I try the P1166 test on page 11-81? Well, I did attempt to but at step 4 the voltage was only 3V not 12V. Step 5 did have 12V.

I'm not exactly sure how to proceed. I disconnected the PCM connector B, step 7. For Step 9, do I ground the PCM module connector pin 16 to ground or the cable connector B pin 16 to ground? It's not clear, I believe it is the former but clarification would be would be great.

 

For clarification and to answer my previous question, I traced through the wiring diagram on pages 11-13 and 11-15. If the wire harness side of connector B pin 16 is grounded, it will energize the A/F Sensor heater control relay. This will close the relay contacts and apply 12V to pin C13 through the A/F Sensor 1 heater element and onto pin B19. Logic ground or chassis ground is connected to pin B20 thus there should be 12V from B19 to B20. Results forthcoming...

The answer is 12V. All looks good.

 

Looks like you got to step 9 on page 11-81 where you either replace the PCM or fix the blk/wht wire from the a/f sensor to pin B19 on the PCM.

You might want to repeat step 4 on 11-81 just to make sure you had good contact with your volt meter.

You can run a wire from the sensor blk/wht wire to the PCM. Then see if you get 12V on step 4 of the testing on 11-81. You may want to remove the B19 wire from the PCM when you try this. There are some youtube videos on how to properly remove the pin for a PCM.

Here is a video I found.