Hi again Scotty.

It's me again, with the Subaru and the 2003 Toyota Avalon. I'm hoping you will continue to work on my vehicles with me being your hands. I cleared the Subaru and the Toyota PO420 fault yesterday for both vehicles, and they haven't come back.

However, the now Toyota gets a check engine light about 10-15 seconds after the engine is started. The faults displayed now are PO135 and PO155. Both displaying "02 Sensor Heater Circuit". Neither of these faults were displayed previously.

Worked on it for 6 hours today, and in the process of trying to figure out what's going on I measured all of the readings from all of the 02 sensors with my fluke multi-meter. It was a beast getting to the plug for the downstream 02 sensor. Had to take out the passenger seat.

With the engine running at 2K RPM

The two upstream 02 sensors (two of them) read .4 VDC, and the heater has 1.5 Ohms.

The single down stream 02 sensor reads .23-.27 VDC, and the heater has 16.8 Ohms.

Additionally, the temperature before and after the CAT is about a 10 degrees Fahrenheit difference. If memory serves me, I think it was 255F going in, and about 265F after the CAT.

Now here's where things take a weird twist. The live display through the OBDII port for the 02 Sensor 1 displays 0 VDC, and the 02 Sensor 2 only displays an intermittent .03-.05 reading. Maybe this is normal, but I don't know. That's why I'm asking, lol. This is new territory for me.

When I check the 02 sensor monitors through the OBDII, only Bank 1 - Sensor 2 is displayed with the following readings.

TID $07 - Minimum sensor voltage for test cycle (calculated)
Min-0 Value-1.275 Max-1.275 Units-V
TID $08 - Minimum sensor voltage for test cycle (calculated)
Min-0 Value-0 Max-1.275 Units-V
TID $31 - Manufacturer Defined
Min-0 Value-10.2 Max-10.2 Units-Sec
TID $32 - Manufacturer Defined
Min-0 Value-10.2 Max-10.2 Units-Sec
TID $37 - Manufacturer Defined
Min-0 Value-10.2 Max-10.2 Units-Sec
TID $81 - Manufacturer Defined
Min-0 Value-225 Max-255 Units-N/A
TID $82 - Manufacturer Defined
Min-0 Value-225 Max-255 Units-N/A
TID $83 - Manufacturer Defined
Min-0 Value-225 Max-255 Units-N/A
TID $84 - Manufacturer Defined
Min-0 Value-225 Max-255 Units-N/A
TID $85 - Manufacturer Defined
Min-0 Value-225 Max-255 Units-N/A

As far as the engine sound. It purrs SWEET.

I've also checked every single fuse with the multi-meter to verify continuity. I'm now wondering if it could be the wiring harness or the computer board.
What do you suggest I investigate and try next, in order to eliminate the variable and get to the root problem?

Thanks,
Randy

Comments
No. 1-3
ScottyKilmer
ScottyKilmer

on an 03 the sensor 1 bank 1 and sensor 2 bank 2 are the same sensor design, but wires may be different length. but the sensor after the cat is different

Randy
Randy

Scotty,

I've come across some information suggesting it could be a relay in the engine compartment. If all the relays are working, I'm looking at getting two 02 upstream sensors to replace the current ones since the scan shows both are bad. I hope it's that simple.
Is the sensor in the front the same as the sensor in the back? I'm guessing they are, but to be sure I figure I'd ask.

I'm looking at AutoZone. Which one would you recommend?

ScottyKilmer
ScottyKilmer

on the toyota, the heating elements of the oxygen sensors burn out, and you just replace the sensors 99 percent of the time to fix it. PRAY it hasn't shorted out the computer driver circuit. It will run perfectly normally with that problem, but will not pass yearly emisssions testing.

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