1996 Toyota Corolla P0125

P0125 indicates1. bad Thermostat,2. low coolant level,3. bad coolant temperature sensor. Coolant level seems fine. Temperature gauage says, ok, in the middle. I replaced coolant temp. sensor. After 10- 15 minutes check engine light comes back on.
In the past the O2 wires got cut. I reconnected them. I believe on the O2 sensor the wires are Blue and white they connect to brown and grey? Does it matter? Could Thermostat cause this. If Thermostat is stuck open would temp. gauge be stable with needle just a little below the middle.
Help.

I'd try a dealer thermostat!

I think that I remember Toyota mis-defining that code number. It's supposed to refer to the O32 sensor signal or heater or the sensor itself. I think I remember that from somewhere that Toyota mis reads that code.

yes it is actually for the upstram O2.

1. Changed Thermostat, 2.new Coolant Temp. Sensor.
P0125 STILL coms on.
On 1996 1.8L Toyota on the O2 Sensor one wire is blue, the other is white.
They go to a plug that goes to the wire harness on the wire harness the plug has one black wire and one brown wire one of the wires is shielded, or possibly 2 conductor. The conecting plug is missing. Does anyone know what wires on the harness connect to the O2 sensor. Does it make a difference how they connect.

bad after-market sensor or bad splicing job, is it a hard code, does the light come on right away and stay on? good luck

Yes, it makes a difference. Don't try to splice it yourself. Take it to a qualified repair facility and they'll fix the harness properly.

By accident I left coolant temperature sensor disconnected. It generated 2 codes. p0115 and p0125. P0115 is the temperature coolant sensor. P0125 Has to do with not getting into a closed loop circuit. Auto Zone listed the cure for the code (125) as faulty temp. sensor, 2. bad thermostat or3. low on coolant. When I rewired the O2 sensor the Mil went out, no more codes,
From my experience on a Toyota P0125 was a disconnected or bad O2 sensor. Before cat. converter. Code p0115 is disconnected or bad coolant temperature sensor. Not the sensor that controls temp. gauge on dash but sensor that controls fuel mixture. It has a plug with 2 wires connecting. The temp. gauge sensor has one wire,and it is located on the end of the engine very close to the distributor. The coolant temp. sensor is located on the firewall side of the head also close to the distributor but it faces at a right angle to the distributor.