Hi. I have a 2002 SC430 and on the drive home the engine light came on. read it with a cheap hand held scanner- P0125 Insufficient Coolant Temperature for Closed Loop Fuel Control, I replaced the thermostat in case it was stuck open, bled the cooling system several times then replaced the coolant temperature sensor and bled the colling system several more times but the EML will always come back on esactly the same place when I go for a test run (when all parameters are met). I found a few posts saying it is probably B1S1 o2 sensor so I bought Techstream to check, B1S01 was showing 0.00 volts, does this confirm my problem is with B1S01 o2 sensor or the wiring to that sensor rather than another system of the car, I found another thread that VVTiBob kindly posted 0125 error code details and a diagnostic trouble chart to follow so that will be my next port of call.
Before I drove the car home it was very low on fuel (didn't run out), I have reset the P0125 code several times since with rull tank so doubt it is this.
I ran Techstream before and after erasing the code and both times the live data showed o2 sensor B1S1 showing 0.00 volts.
I'm new to techstream so can one of you lovely people have a look to see if i'm heading down the right path. Many thanks.

O2S B1S1 is showing 0.000 volts

 

Hi I would monitor os2 b1s1 .. all 02 a/f sensors b1 sensors 1 and 2 .. b2 sensor 1 and 2 see if there modulating the same ... I would replace both sensors on Bank 1 sensor 1 and sensor 2 ... 0.000 not good flat line

 

Make sure that you only use Denso products in your Lexus and Toyota...

 

There's also the possibility of a bad connector or a cut wire.

 

BINGO. We hve a winner! Harold57, I spent today testing wires/more test drives and found open circuit between HT on the o2 connector and HTL on the ECU connecor. Closer inspection found a broken wire to the connector block for the o2 sensor on Bank 1 Sensor 1. Thanks for alll the help and advice.

 

That's great news grahamtabb. Congrats.