P0135 on the 2021 Honda Pilot
The 2021 Honda Pilot uses the 3.5L J35Y6 V6 engine producing 280 horsepower, paired with either a 9-speed automatic (most trims) or 6-speed automatic (base LX). The P0135 code indicates the heater circuit in the Bank 1 Sensor 1 oxygen sensor has malfunctioned. On the Pilot's transverse-mounted V6, Bank 1 is the rear bank (closest to the firewall), and Sensor 1 is the upstream sensor before the catalytic converter on that bank.
The V6 O2 Sensor Heater System
The Pilot's 3.5L V6 uses four O2 sensors: two upstream and two downstream. The Bank 1 upstream sensor heater is critical for quickly establishing closed-loop fuel control on cylinders 1, 3, and 5 after cold starts. The heater brings the sensor to operating temperature in approximately 20-30 seconds, versus 3-5 minutes from exhaust heat alone. When the heater fails, cold-start emissions and fuel consumption increase.
Causes
- Heater element burnout: At 3-5 years old, the 2021 Pilot may have 30,000-80,000 miles. While early for heater failure, the V6's higher heat output and proximity of the rear bank to the firewall (trapped heat) can accelerate degradation. Frequent short-trip driving multiplies thermal cycles.
- Blown heater fuse: The Pilot's underhood fuse box has a dedicated O2 heater fuse. Always check this first as it is a sub-$10 repair.
- Connector corrosion: The rear bank O2 sensor connector on the Pilot is positioned where it can collect road spray and salt. Corroded pins disrupt the heater circuit.
- Wiring damage: The rear bank sensor wiring routes through a congested area behind the engine near the firewall. Heat soak in this area can damage wire insulation over time.
Symptoms
Check engine light illuminates. The Pilot may idle slightly rough during the first minute or two of a cold start. Fuel economy may decrease from the typical 20-27 MPG range on short trips. Once warm, the sensor operates normally via exhaust heat. The 9-speed automatic transmission behavior is not affected by this code.
Diagnosis
- Check the O2 heater fuse in the underhood fuse box.
- Locate the Bank 1 (rear) upstream sensor connector and disconnect it.
- Measure heater resistance: 2-15 ohms normal, open circuit = failed heater.
- Verify 12V power at the heater power pin with key on.
- Inspect the connector for corrosion and the wiring for heat damage in the area behind the engine.
Repair Costs
The 2021 Pilot should be within emissions warranty (8 years/80,000 miles). Out-of-pocket: OEM sensor: $90-$180. Aftermarket: $45-$90. Dealer labor for rear bank: $150-$280 (harder access). Total dealer: $240-$460. Independent shops: $170-$340. Fuse: under $10. Honda dealer labor: $125-$175/hour.
DIY
The rear bank upstream O2 sensor on the Pilot is more challenging to access than front bank sensors. You will need to work from below or reach over the engine. The V6 engine takes up most of the bay, limiting workspace for the rear bank. A 22mm O2 sensor socket with a universal joint and long extension is recommended. This is a moderate DIY job. Check the fuse first for the easy win.