P0135 on the 2019 Ford Explorer
The 2019 Ford Explorer is the final year of the fifth generation, available with the 3.5-liter Ti-VCT V6 producing 290 horsepower, the 2.3L EcoBoost four-cylinder, or the 3.5L EcoBoost twin-turbo V6 in Sport and Platinum trims. A P0135 code indicates the Bank 1 upstream O2 sensor heater circuit has malfunctioned. At six to seven years old, this is a common failure point regardless of engine option.
Fifth-Gen Explorer Platform
The 2019 Explorer uses a transverse engine layout with front-wheel-drive-based AWD, different from the newer rear-drive-based models. On the 3.5L V6, Bank 1 is typically the side of the engine closest to the firewall. The upstream sensor on that bank is harder to access in the transverse configuration. On the 2.3L EcoBoost four-cylinder, there is only one bank with a turbo-adjacent sensor.
Likely Causes
- Age-related heater burnout (High Likelihood): Six to seven years of thermal cycling has worn the Motorcraft sensor's heater element. The heater coil accumulates micro-cracks from repeated expansion and contraction until it finally breaks. This is the most common cause at this vehicle age.
- Wiring corrosion and heat damage (Medium Likelihood): Years of exposure to exhaust heat, moisture, and road salt degrade wiring insulation and corrode connector pins. The 2019 Explorer's transverse engine layout puts sensors in tight spaces where heat accumulates.
- Blown heater fuse (Medium Likelihood): Always check the underhood power distribution box for the O2 heater fuse. A blown fuse from aged wiring developing a short is common at this vehicle age.
- Ground connection corrosion (Low Likelihood): Six years of environmental exposure can corrode ground points, increasing circuit resistance. The PCM detects reduced heater current and sets the code.
Diagnosis Steps
Warranty Check
The 2019 Explorer may still be within the 8-year/80,000-mile federal emissions warranty through 2027 if under the mileage limit. Verify with your Ford dealer before spending money.
Fuse and Visual Inspection
Check the O2 heater fuse. Then locate the Bank 1 upstream sensor. On the 3.5L V6, this is on the rear exhaust manifold near the firewall in the transverse layout, making access more difficult. On the 2.3L EcoBoost, it is near the turbo. Inspect wiring and connectors for six years of wear.
Resistance Testing
Disconnect and test heater resistance: 3 to 15 ohms normal for Motorcraft sensors. After six years, if resistance is borderline, replace the sensor. Also check for battery voltage at the harness connector.
Sensor Removal
After six years, expect the sensor to be seized in the exhaust manifold. Apply penetrating oil and soak for at least 30 minutes. The transverse V6 layout makes Bank 1 access challenging, potentially requiring removal of air intake components for clearance.
Repair Costs
Under warranty if eligible: free. Out of pocket: Motorcraft sensor $60 to $140, shop labor $120 to $200 (higher due to transverse V6 access). Total: $180 to $340. DIY on the V6 is challenging due to the rear bank access. The 2.3L EcoBoost is somewhat easier to reach. Budget 45 minutes to an hour for experienced DIYers.
Why Fix It Now
The fifth-generation Explorer is a proven platform that many owners keep for years. At six to seven years old, protecting the catalytic converters with a simple sensor replacement is a smart investment. Catalytic converter replacement on the 3.5L V6 Explorer runs $800 to $2,000. The $150 sensor fix now prevents the much costlier converter repair later.