P0135 Toyota Highlander
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 Toyota Highlander 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 Toyota Highlander.
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 Toyota Highlander.
Common Causes on Toyota Highlander
- Bank 1 Sensor 1 O2 sensor heater circuit failed — blown heater element inside Denso sensor
- Blown O2 sensor heater fuse in engine compartment fuse box
- Open or shorted wire in O2 heater circuit
- Corroded O2 sensor connector
Symptoms
- Check Engine Light on
- Extended warm-up time for closed-loop fuel control
- Slightly rich running during first few minutes of driving
- Failed emissions readiness check
Notes for Toyota Highlander
Always check the fuse first — a $1 fuse fix saves you a $100 O2 sensor replacement.