Hello everyone, so I'm starting this new thread because the last one I did was too long, probably no one new would want to read a 70 reply thread, so here's a new one.

As some of you know I have an 04' LS430, I did a thread earlier this year explaining my problem. the car had a flashing check engine light with a P0031 code plus some other codes related to misfires in the bank 1 cylinders (1,3,5,7) I think those are P0301 up to P0307.

I have a Toyota Techstream software and I checked the voltage on the O2 sensors, the B1S1 sensor read 1.27v even with the car turned off while the other 3 sensors read 0.00v, I disconnected the O2 sensor from the harness and Techstream read 0.00v on that sensor so I thought that the problem was the sensor itself and not the wiring shorted, but today I replaced that sensor with an OEM Denso one and it still read 1.27v on Techstream so I'm not sure what to think as of right now, I wanted to check wiring but I really can't read diagrams, I don't have the knowledge to understand them (I'll try to learn how). I did a computer reset after I replaced the sensor and the car as of right now runs fine, still I know it's temporary and it still shows a P0031 code.

¿Any suggestions on how to check wiring? Test light? Multimeter?

Relating to P0301-P0307 I already swapped the coils and spark plugs.

 

P0031 means Bank 1 Sensor 1 HEATER circuit of the O2 sensor has abnormally low current. When the heater operates (meaning the +B signal line is greater than 11.5V), the heater should draw 0.4-1.0 amps. If the current draw is less than 0.25A, this code is thrown.

This heater circuit failure is not directly related to misfires, meaning that while a failed heater can't cause misfires, a rat that chewed through some cables could cause both problems.

For P0031, use a multimeter to check:
ECM connector E6, pin 24, to connector E7, pin 1, should be 9-14V
O2 Sensor connector H9 (B1S1), pin 1, to ECM connector E6, pin 24, should be <1 Ohm
H9-1 to ground should be >10 kOhms
E6-24 to ground should be >10 kOhms
H9-2 to pin 3 underneath the EFI main relay should be <1 Ohm
H9-2 to ground should be >10 kOhms


To verify O2 sensor operation aside from the heater (which you probably don't need to do since you don't have actual O2 sensor DTCs), use Techstream to graph your fuel injector volume and O2 sensor voltage. Using the Active Test, control the injection volume at idle. Your O2 sensor voltage should fluctuate nearly lock-step with injector volume, a minor time lag is normal. If your O2 sensor voltage is flat (has no reaction to changing fuel amount), then your sensor is bad. There are other ways the sensor can be bad, you'll know when you get a code, then you can follow the service manual accordingly.

To figure out your misfires, you're going to look at the freeze frame data in Techstream, which shows what was going on at the time of the code. Sounds like something on bank 1 is broken, check wiring harness to the coils and plugs, check fuel rail, camshaft oil control valve, check everything relating to bank 1.

 

you may want to verify your OCV is operating properly.