The code refers to the front oxygen sensor on bank 1. That O2 sensor needs to be replaced or the wiring has come loose or is shorted out.
Trouble code P0135 means: HO2S Heater Performance Sensor 1
Trouble code P0135 means:O2 sensor heater circuit malfunction (Bank 1 Sensor 1)
Trouble code P0135 means: O2 Heater Circuit (Bank 1, Sensor 1)
Trouble code P0135 means:O2 sensor heater circuit malfunction (Bank 1 Sensor 1)
Trouble code P0135 means:O2 sensor heater circuit malfunction (Bank 1 Sensor 1)
Trouble code P0135 means:O2 sensor heater circuit malfunction (Bank 1 Sensor 1)
Trouble code P0135 means:O2 sensor heater circuit malfunction (Bank 1 Sensor 1)
Trouble code P0135 means:O2 sensor heater circuit malfunction (Bank 1 Sensor 1)
Trouble code P0135 means:O2 sensor heater circuit malfunction (Bank 1 Sensor 1)
Trouble code P0135 means:O2 sensor heater circuit malfunction (Bank 1 Sensor 1)
It means your sensor heater in Sensor 1 or Bank 1 is malfunctioning. Get it replaced.
P0135 -- Oxygen Sensor Heater Circuit Malfunction This does not necessarily mean the O2 sensor is bad. It just means it is being effected. Odds are it is bad especially if the car has over 50,000 miles on it.