1. What is P0031 in Ford F-150?

The P0031 OBD-II code stands for HO2S Heater Control Circuit Low (Bank 1 Sensor 1). For the Ford F-150 (2018-2024)—America’s best-selling pickup—this code targets the upstream oxygen (HO2S) sensor in the 2.7L EcoBoost V6 engine (standard in XLT, Lariat, and XL trims).

The F-150’s upstream HO2S sensor (Bank 1 Sensor 1) monitors exhaust oxygen levels to adjust fuel injection—critical for meeting emissions standards and maintaining 22–24 MPG highway efficiency. A built-in heater warms the sensor to 600°F+ quickly (within 30 seconds of startup) for accurate readings. P0031 triggers when the PCM detects low voltage (<9V) in the sensor’s heater circuit—signaling a faulty sensor, broken wiring, or PCM driver failure.

F-150 Specific Note: This code is widespread in 2019-2023 F-150 2.7L EcoBoost models, per Ford Technical Service Bulletin (TSB) 21-1245. The 2.7L’s turbocharged exhaust generates extreme heat, which degrades the sensor’s heater element over time—especially in trims used for frequent short trips (sensor never fully heats up, accelerating wear).

2. Common Causes of P0031 in 2018-2024 F-150

P0031 in F-150 2.7L EcoBoost models stems from HO2S sensor heater circuit issues—below are real-world cases diagnosed with the ICARZONE MA200 V6:

• Faulty Upstream HO2S Sensor (2020 F-150 XLT 2.7L): An XLT owner with 68,000 miles reported Check Engine Light and reduced MPG. The MA200 V6’s HO2S Heater Voltage Test showed 7.2V (normal: 9–14V). Replacing the sensor with OEM #DL3Z-9F472-A (per TSB 21-1245) fixed P0031.
• Shorted Sensor Wiring (2019 F-150 Lariat 2.7L): A Lariat owner’s P0031 reappeared after sensor replacement. The MA200 V6’s Circuit Continuity Test found 0Ω resistance (normal: <0.5Ω but not shorted). Road debris had frayed the sensor’s power wire, causing a short to ground—repairing with heat-shrink connectors resolved the issue.
• PCM Heater Driver Failure (2018 F-150 XL 2.7L): An XL owner’s P0031 persisted after wiring repairs. The MA200 V6’s PCM Output Test confirmed the sensor heater driver circuit was non-functional. Updating the PCM firmware (v2.3.0) via MA200 V6 fixed the driver logic (addressed in TSB 22-003).
• Loose Sensor Connector (2021 F-150 King Ranch 2.7L): A King Ranch owner’s P0031 was intermittent. The MA200 V6’s Live Voltage Test showed voltage dropping to 6V when hitting bumps. The sensor connector was loose—securing it with dielectric grease and zip ties eliminated the fault.

3. Key Symptoms of P0031 in F-150 2.7L EcoBoost

P0031 symptoms in the F-150 focus on emissions and efficiency—watch for these signs that affect fuel economy and engine performance:

4. F-150 Trims/Engines Prone to P0031

Ford service data highlights these 2018-2024 F-150 configurations with the highest P0031 occurrence rates (all 2.7L EcoBoost V6):

5. Diagnose P0031 with ICARZONE MA200 V6

Diagnose P0031 in your F-150 2.7L EcoBoost accurately with the MA200 V6’s Ford-specific HO2S tools. Follow these steps (engine off, key in "ON" position):

Case Example: A 2019 F-150 XLT failed Step 2 (6.8V) and Step 5 (TSB 21-1245 eligible). The MA200 V6’s Component Location Tool guided sensor access (driver’s side exhaust pipe, 6 inches before the catalytic converter). Replacing the sensor fixed P0031—verified by test drive (restored MPG to 23 highway).

6. How to Fix P0031 in F-150 2.7L EcoBoost

Resolve P0031 in your F-150 with these MA200 V6-verified solutions—tailored to the 2.7L EcoBoost’s HO2S system:

1. Replace Upstream HO2S Sensor (Most Common Fix for TSB 21-1245)

1. Confirm sensor failure via MA200 V6’s Step 2. Raise the F-150 with jack stands (secure to frame rails) to access the exhaust system.
2. Locate Bank 1 Sensor 1: Mounted on the driver’s side exhaust pipe, 6 inches before the catalytic converter (4-pin electrical connector).
3. Disconnect the sensor’s connector (press the tab to release) and spray penetrating oil on the sensor threads (prevents seizing).
4. Remove the old sensor with an O2 sensor socket (22mm) and ratchet—turn counterclockwise slowly to avoid damaging the exhaust pipe.
5. Install an OEM upstream HO2S sensor:
   • 2018-2020 F-150: #DL3Z-9F472-A
   • 2021-2024 F-150: #BL3Z-9F472-A (updated heater element)
   Apply anti-seize to the sensor threads (avoid getting on the tip—prevents contamination).
6. Torque the sensor to 30 ft-lbs, reconnect the connector, and lower the truck. Clear P0031 with MA200 V6 and test drive—verify sensor warm-up time <30 seconds.

2. Repair Shorted/Open Sensor Wiring

1. Confirm wiring issue via MA200 V6’s Step 3. Trace the sensor’s wiring harness from the sensor to the PCM (runs along the frame rail, driver’s side).
2. Look for frayed insulation, melted sections, or loose connectors. Cut out damaged wire segments (add 1 inch on each side of the fault).
3. Use heat-shrink butt connectors (#Dorman 800-125) to splice new 16-gauge automotive wire—crimp connectors and apply heat to seal the shrink tube.
4. Secure the repaired harness to the frame rail with zip ties (avoids contact with hot exhaust components). Reconnect the sensor and PCM connectors.
5. Retest continuity with MA200 V6 (should read <0.5Ω) and clear P0031. Test drive to confirm no voltage drops during acceleration.

3. Update PCM Firmware (TSB 22-003)

1. Confirm PCM driver failure via MA200 V6’s Step 4. Ensure the F-150 is parked in a well-ventilated area (update takes 15–20 minutes).
2. Connect the MA200 V6 to the OBD-II port and select "Ford" > "F-150" > "2.7L EcoBoost" > "PCM" > "Firmware Update."
3. The MA200 V6 will detect the current PCM version and download the latest update (matches TSB 22-003 specs for HO2S heater control).
4. Do not turn off the engine or disconnect the MA200 V6 during the update. The tool will alert you when complete.
5. Restart the engine, retest sensor voltage with MA200 V6 (Step 2), and clear P0031. Verify the sensor heater receives 9–14V at startup.

7. P0031 Repair Costs & Maintenance Tips

P0031 repair costs for the F-150 2.7L EcoBoost vary by cause. Use this table to budget:

Maintenance Tips for F-150 2.7L EcoBoost Owners

• XLT (short trip users): Replace the upstream HO2S sensor every 70,000 miles (preventive) — use OEM #BL3Z-9F472-A for 2021+ models to avoid TSB 21-1245 wear.
• Inspect the sensor connector during oil changes—apply dielectric grease to pins to prevent corrosion (critical for cold/wet climates).
• Avoid driving through deep water or mud—water can short the sensor’s wiring. If submerged, dry the connector with compressed air immediately.
• Take monthly 30-mile highway trips (60+ MPH) to fully heat the sensor—prevents carbon buildup on the heater element.
• Perform the MA200 V6’s HO2S Health Check every 15,000 miles — monitor heater voltage to catch issues before P0031 triggers.

8. F-150-Specific FAQs