Automotive Emissions & Fuel SystemLow to Medium Severity
O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 1)
Applies to: OBD-II Universal
Safety & Usage Advisory
Can you still drive / use device? Yes, vehicle is safe to drive, but will stay in open-loop mode longer upon startup.
Estimated Repair Cost
$80
$80 - $240 (DIY Sensor: $45)
Diagnostic Category
Automotive Emissions & Fuel System
OBD-II Universal
Fix Difficulty
Beginner
~30-60 Mins Required
Common Symptoms
- Check Engine Light on
- Slightly increased fuel consumption on short trips
- Failed state emissions inspection
Root Causes
- Burnt-out internal heating element in upstream oxygen sensor
- Blown O2 sensor heater fuse
- Melted or damaged sensor wiring near exhaust manifold
- Excessive circuit resistance
Step-by-Step Instructions to Fix P0135
1
Check the Heater Fuse
Locate the under-hood fuse box and test the O2 sensor heater fuse with a multimeter or test light.
2
Measure Sensor Heater Resistance
Unplug the Bank 1 Sensor 1 connector and test resistance between the two heater pins (typically 3 to 15 ohms).
3
Replace Upstream O2 Sensor
Use an O2 sensor socket wrench to remove the old sensor from the exhaust manifold and install an OEM-spec replacement with anti-seize on the threads.
How to Prevent P0135 in the Future
- Address engine oil-burning or misfires promptly to prevent premature O2 sensor contamination
P0135 Troubleshooting FAQs
Bank 1 is the cylinder bank containing Cylinder #1. Sensor 1 is the upstream sensor located before the catalytic converter.