P0135 Ford Bronco
O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 1) · Powertrain Code · Low · Repair: Moderate
What is P0135?
The heater circuit in the upstream O2 sensor on bank 1 has failed, delaying sensor warm-up.
When the Ford Bronco 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 Ford Bronco.
This repair is rated moderate, meaning some experience and specialty tools required.
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 Ford Bronco.
Common Causes on Ford Bronco
- Failed O2 sensor heater element (bank 1 sensor 1)
- Blown O2 sensor heater fuse in the under-hood fuse box
- Corroded wiring or connector at the upstream O2 sensor
- PCM heater control circuit failure (rare)
Symptoms
- Check engine light
- Extended warm-up period for fuel trim control
- Slightly poor cold-start fuel economy
- May fail emissions test
Notes for Ford Bronco
Check the fuse first — on many Ford trucks, the O2 heater fuse is in the battery junction box and costs nothing to replace.