P0135 Kia Forte
O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 1) · Powertrain Code · Low · Repair: Easy
What is P0135?
The heater circuit in the upstream O2 sensor on bank 1 has failed, delaying sensor warm-up.
When the Kia Forte triggers code P0135 (o2 sensor heater circuit malfunction (bank 1, sensor 1)), it typically points to an issue in the powertrain system. Below you'll find the most common causes, symptoms, and repair options specific to the Kia Forte.
This repair is rated easy, meaning basic tools, no lift needed.
Diagnostic data on this page is compiled from publicly available repair resources and technical service bulletins. Always have a qualified mechanic confirm the diagnosis before authorizing repairs on your Kia Forte.
Common Causes on Kia Forte
- Burned-out O2 sensor heater element (Bank 1 Sensor 1)
- Blown O2 heater fuse or relay
- Corroded O2 sensor connector from road salt or moisture
- ECM heater driver circuit failure (rare)
Symptoms
- Check Engine Light on
- Extended time to enter closed-loop fuel control
- Slightly rich running when cold
- Failed emissions test
Notes for Kia Forte
This is a heater circuit code; the sensor itself is usually the failure point on Kia vehicles.