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P0135 on a 2017 Ford F-150

O2 Sensor Heater Circuit (Bank 1 Upstream)

Severity: moderate Safe to drive (short term) Pickup Truck 2015-2019 Ford F-150

What does P0135 mean on a 2017 Ford F-150?

P0135 is set when the ECM detects that the heater element built into the Bank 1 upstream oxygen sensor is not drawing the expected current when commanded on. Zirconium O2 sensors only produce a usable signal above approximately 350 °C / 660 °F, so they include an internal heater that brings them to operating temperature quickly after cold start. P0135 means that heater is open, shorted, or being under-powered.

Symptoms on a 2017 Ford F-150

Likely causes on a 2017 Ford F-150

  1. Failed O2 sensor heater element (open or shorted internally) Most common
    Estimated repair: $150– $450
  2. Blown O2 heater fuse Common
    Estimated repair: $5– $30

    Always check the fuse before condemning the sensor.

  3. Damaged sensor wiring (chafed against exhaust) Common
    Estimated repair: $80– $350
  4. Corroded O2 sensor connector Common
    Estimated repair: $30– $200
  5. Failed O2 heater relay (on vehicles with one) Occasional
    Estimated repair: $30– $150
  6. Failed PCM driver for the heater circuit (rare) Rare
    Estimated repair: $400– $1,500

How to diagnose this on a 2017 Ford F-150

  1. Check the O2 heater fuse first

    Most vehicles route O2 heater power through a dedicated fuse, usually labeled "O2H" or "O2 SNSR" in the underhood fuse box. Replace any blown fuse with the exact amperage rating. If the fuse blows again immediately, the heater or its wiring is shorted.

    Tools: Replacement fuse, Fuse puller

  2. Measure heater resistance at the sensor

    Unplug the Bank 1 upstream O2 sensor. Measure resistance across the heater terminals (typically the two same-color wires — consult the wiring diagram). Expected resistance is approximately 3 to 15 Ω cold, depending on the sensor. Infinite resistance means an open heater; near zero means a shorted heater.

    Tools: Multimeter, Wiring diagram

  3. Verify power and ground at the connector

    With the key on and engine running, back-probe the heater power and ground wires. Battery voltage should be present on power and a clean ground on the other side. Missing voltage points to the fuse, the wiring, or the PCM driver.

    Tools: Multimeter, Back-probe pins

  4. Measure heater current draw

    A working heater draws approximately 0.8 to 2 A depending on sensor design. Use a low-current clamp around the heater wire, or a multimeter in series. Current of 0 A with voltage present means the heater is open. Current well above 2 A means the heater is partially shorted and will fail soon.

    Tools: Multimeter with current function, Low-current clamp (preferred)

  5. Inspect the sensor and its wiring for physical damage

    O2 sensor harnesses run close to hot exhaust components and are a common chafing victim. Inspect the wiring from the connector to the sensor body. Heat-damaged insulation, melted plastic, or visible copper requires harness repair or replacement, not just a new sensor.

    Tools: Flashlight, Wire repair supplies

Common fixes

About the 2015-2019 Ford F-150

The 2015-2019 Ford F-150 was commonly sold with the following powertrains: 3.5L EcoBoost V6, 5.0L V8, 2.7L EcoBoost V6. Common trims include XL, XLT, Lariat, King Ranch, Platinum.

Why heater failure matters

Zirconium O2 sensors produce no usable signal until they reach about 350 °C. Without the heater, the sensor waits for exhaust heat to bring it up to temperature — which can take 5+ minutes of driving. During that period the ECM runs in “open loop” mode, using a calibrated fueling map rather than O2 feedback. This is fine briefly but causes poor cold-running emissions and 10–20 % worse fuel economy while the heater is dead.

P0135 with the sensor only weeks old

Aftermarket O2 sensors fail at much higher rates than OEM. If P0135 appeared shortly after an O2 sensor replacement with a non-OEM part, the new sensor itself is the most likely problem. Warranty-exchange for an OEM-equivalent before chasing the wiring.

Heater current and the “weak heater”

A heater that draws low current but is not fully open is a “weak” heater. It will warm the sensor partially, allowing the sensor to work but slowly. The ECM eventually sets P0135 even though the heater is not fully dead. A current measurement is the only reliable way to catch this failure mode — a simple resistance check often misses it.

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