Hey Scotty, Glad to be here. Recently picked up a 3rd gen 2000 series 4Runner in beautiful shape with 240,000 miles and the v6. About a week ago it started reading a p1135/p0125 error codes. From my research I was told to replace the B1 S1 o2 sensor. I did that today and cleared the code and it was back within 1 mile. Any ideas? It’s driving me insane.
if it matters, it’s a 2000 5speed.
Given that you've purchased a nearly 1/4-century-old vehicle with high mileage problems are to be expected.
Given that P1135 refers to the Bank1, Sensor 1 heater circuit. Before replacing the O2 sensor did you check to see if +12V is being applied to the O2 sensor heater?
P0125 is not an O2 sensor issue, it refers to a cooling system problem where the engine is not reaching sufficient temperature for closed-loop operation:
A stuck open thermostat would be the primary suspect but as noted above there are other potential causes, such as the temperature sensor or its wiring.
You can find a shop manual for that vehicle at charm.li which may help.
