1999 Rx300

[dasadler]

My son's RX300 recently had the check engine light come on and the diagnostics showed P0125 (Insufficient Coolant Temp. for Closed Loop
Fuel Control) & P1135 (A/F Sensor Heater Circuit Malfunction (Bank
1 Sensor 1).

We replaced the coolant temp sensor and the A/F heater ration temp. sensor.

After clearing the codes from memory, we drive it a few miles and the codes return. Clear & return, Clear & return.

What else might we have missed that causes the problem?

Thanks in advance.

p.s. the car only has 157K miles.