P0155 Code: Ford Escape (2020-2024) - Causes, Symptoms & Fixes

P0155 Diagnostic Guide for 2020–2024 Ford Escape (OBD-II Code)

Important data note (data limitations)

• In the provided NHTSA/complaint data for Ford Escape (2020–2024), there are no documented complaints specifically for P0155. The three owner complaints cover P0172, P0455, and P0420. There are no recalls listed for this model in the data.
• Consequently, this guide uses general OBD-II and Ford-specific knowledge for O2 sensor heater codes, tailored to the Ford Escape platform, with clear notes where Ford-specific quirks might apply. Prices are 2025 estimates and can vary by region, dealer, and technician.

CODE MEANING AND SEVERITY

• Code: P0155
• Full meaning: OBD-II Powertrain DTC P0155 = O2 Sensor Heater Circuit Malfunction (Bank 2 Sensor 1)
  • Bank 2 Sensor 1 refers to the upstream oxygen sensor on the secondary bank (the “other” side of the engine in a V-engine configuration; on some Ford layouts this maps to the O2 sensor before the catalytic converter on the opposite bank from Bank 1). The key point is: the heater element in the Bank 2 Sensor 1 is not heating properly.
• What it implies:
  • The oxygen sensor heater isn’t behaving as designed, so the sensor may take longer to reach its operating temperature.
  • Until the sensor warms up, the sensor readings can be slow to reflect actual exhaust conditions, which can cause the engine to run in open-loop longer, affecting fuel trim and emissions.
• Severity:
  • Not typically an immediate safety hazard, but it can cause higher emissions, degraded fuel economy, and potential catalytic converter stress if the condition persists.
  • The vehicle may still run, but the ECU may rely on default/rough fuel trims until the sensor heats up enough to read properly. In some cases it can trigger an MIL (check engine light) and set other related codes (e.g., P0135, P0155 family, or P0420 if emissions monitoring is affected).

COMMON CAUSES ON FORD ESCAPE

• Faulty upstream O2 sensor (Bank 2 Sensor 1) heater element
• Damaged or corroded sensor harness or connector (insulation wear, cracked pins, poor pin-to-pin contact)
• Blown fuse or fusible link protecting the O2 sensor heater circuit
• Wiring harness damage or chafing (especially where it runs near exhaust components or along the engine bay)
• Poor or intermittent electrical ground reference for the heater circuit
• ECU/PCM control circuit fault (less common, but possible if the heater drive circuit is damaged)
• Contamination, coolant leakage, or exposure to high heat that degrades the heater element or its wiring
• In some Ford layouts, a misidentified sensor (i.e., Bank 2 Sensor 1 vs. another bank’s sensor) can occur in scans; always verify the exact sensor location in your vehicle’s service manual or with an OEM diagnostic tool

SYMPTOMS YOU MIGHT NOTICE

• Check Engine Light (MIL) is on or blinking (often steady, but can be intermittent)
• Increased tailpipe emissions or failing an emissions test
• Possible slight drop in fuel economy or changes in long-term fuel trims on the scanner
• Inconsistent idle or engine running conditions when the engine is cold or during warm-up (less likely to be dramatic; some vehicles run normally once warmed)
• O2 sensor readings may appear slow to respond on scan data if the heater isn’t warming the sensor
• No dramatic drivability symptoms in many cases, but drivetrain performance can be impacted if the ECU relies on incorrect sensor data during open-loop operation

DIAGNOSTIC STEPS (step-by-step)

Note: Always start with a diagnostic scan to confirm P0155 and capture freeze-frame data and live sensor readings.

• A. Confirm the code and data

  • Use a capable OBD-II scan tool to confirm P0155 and to view live data for Bank 2 Sensor 1 (voltage, heater current/ON-time if supported, sensor 1 upstream data, and related bank data).
  • Check for related or concurrent codes (e.g., P0135, P0154, P0155, P0156) and any catalyst/oxygen sensor-related fault codes (P0420, P0430, etc.).

• B. Visual and physical inspection

  • Inspect the Bank 2 Sensor 1 O2 sensor and its wiring harness for:
    • Damaged insulation, open wires, or pin corrosion
    • Loose connectors, corrosion in the sensor connector, or bent pins
    • Heat/smoke damage near exhaust components
  • Inspect the O2 sensor mounting area for exhaust leaks or contamination that could affect readings.
  • Check fuses/relays tied to the O2 sensor heater circuit per the owner/maintenance manual.

• C. Electrical tests (when safe to do so)

  • Verify supply voltage and ground:
    • With ignition ON (engine OFF) verify there is the correct reference voltage and ground on the heater circuit pins of the sensor connector (as per service manual).
  • Heater circuit resistance test:
    • Disconnect the sensor, measure the heater resistance with a multimeter across the heater pins.
    • Compare to OEM specification. A very high resistance or open circuit indicates a faulty sensor.
  • Continuity and shorts:
    • Check for shorts to power or ground along the harness lead; look for pin-to-pin short or pin-to-ground faults.
  • If available, perform a current/voltage test on the heater circuit while the engine is cranking or running (some scanners can show heater current). A healthy circuit should show heater current when commanded ON by the PCM.
  • Check for intermittent connections by gently wiggling the connector and harness with the ignition on to see if the fault reappears (could indicate a loose connection).

• D. Functional test

  • If the heater is commanded ON by the PCM, observe whether the sensor begins to heat (voltage stabilization or a change in sensor signal as it warms). A heater that never heats or only heats intermittently supports a faulty sensor or wiring problem.

• E. Decide on repair path

  • If the sensor heater shows open or short, or if the connector/wiring is damaged beyond simple repair, replace the upstream Bank 2 Sensor 1 oxygen sensor.
  • If the heater circuit fuse/relay is blown, replace the fuse/relay and re-test.
  • If wiring harness damage is found but repairable, perform wiring repair and re-test.
  • If all wiring/test results are normal but the fault persists, suspect a PCM/sensor driver issue and consult a dealer or qualified shop for advanced diagnostics.

RELATED CODES

• O2 sensor heater circuit codes often appear in families. Related or commonly seen codes include:
  • P0135: O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 1)
  • P0130/P0131/P0132/P0134: Misc. Bank 1 Sensor 1 gas sensor/readings and heater faults
  • P0150/P0151/P0152/P0154/P0156/P0157: Similar heater-related faults for Bank 2 sensors (depending on exact sensor and bank)
• Emissions and catalyst codes may appear later if the ECU runs in alternate fuel trims for extended periods due to faulty sensor data (e.g., P0420/P0430 for catalyst efficiency).

REPAIR OPTIONS AND COSTS (2025 PRICING, USD)

Notes:

• Prices vary by region, vehicle trim, OEM vs aftermarket parts, and labor rates. These ranges are typical across many shops and DIY parts sources for 2025.

• Option A: Replace Bank 2 Sensor 1 O2 sensor (upstream sensor)

  • Parts: $60–$200 (often $100–$170 for OEM-equivalent or reputable aftermarket)
  • Labor: 0.3–0.8 hours
  • Estimated total: $120–$350 (vehicle-dependent)
  • Notes: This is the most common fix if the heater is confirmed to be open/short or if the wiring is intact but sensor heating fails.

• Option B: Repair or replace O2 sensor wiring/connector

  • Parts: typically minimal; connector or wiring harness segments if damaged
  • Labor: 0.5–1.5 hours (may be higher if harness routing is difficult)
  • Estimated total: $120–$400
  • Notes: If damage is localized and repairable, this can be cheaper than full sensor replacement.

• Option C: Check/replace fuse or relay for O2 heater circuit

  • Parts: $0–$20
  • Labor: minimal (0.1–0.3 hours)
  • Estimated total: $10–$50
  • Notes: A blown fuse/relay is a common easy fix; ensure the heater circuit remains within spec after replacement.

• Option D: PCM/ECU diagnostics or replacement (rare)

  • Parts: $400–$1,000+ (used vs refurbished PCM pricing varies)
  • Labor: 1–3+ hours
  • Estimated total: $500–$2,000
  • Notes: Consider only if wiring is sound and the PCM output is confirmed faulty via OEM service procedures.

• Option E: Sensor replacement as a diagnostic step (if not initially replacing the wrong sensor or if Bank 2 Sensor 1 identification is uncertain)

  • See above for typical costs.

DIY vs PROFESSIONAL

• DIY feasibility:
  • Replacing an upstream O2 sensor is a common DIY job for many car owners with basic tools (socket/set, anti-seize compound for sensor threads, safety gear).
  • Pros: Lower cost, instructional videos, hands-on satisfaction.
  • Cons: Risk of cross-threading, exhaust exposure to hot components, misidentification of the correct sensor, potential need for exact Ford-specific sensor (OEM vs aftermarket), and the need to clear DTCs after replacement.
• When to call a professional:
  • If you’re uncertain about which sensor is Bank 2 Sensor 1 in your engine layout, if you don’t have the right sensor socket or anti-seize, or if you suspect wiring/fuse/PCM issues.
  • If a diagnostic scan reveals intermittent heater current issues or if you suspect PCM wiring faults, a shop with OEM scan tools and wiring diagrams is recommended.
  • If you’re not comfortable with working around exhaust and electrical systems, or if a bank misidentification could lead to incorrect parts replacement.
• Steps for a careful DIY replacement (high level):
  • Gather the correct Ford One-Stage or OEM-equivalent upstream O2 sensor for Bank 2 Sensor 1.
  • Disconnect the battery (optional but recommended for electrical safety and diagnostic reset).
  • Remove the old sensor using a proper O2 sensor socket; apply anti-seize to the new sensor threads (per sensor manufacturer instructions) and install to the manufacturer torque spec.
  • Reconnect the harness, clear codes with a scan tool, and test drive to confirm DTCs do not return.
  • If codes persist, revisit diagnostic steps or bring to a professional for wiring and PCM checks.

PREVENTION

• Regular maintenance and checks:
  • Use quality fuel and periodically inspect/replace O2 sensors per OEM maintenance intervals (often around 60k–100k miles, but check your vehicle's service manual).
  • Avoid repeated short trips that prevent the O2 sensors from reaching operating temperature; longer highway drives help sensors heat up and operate correctly.
  • Inspect wiring harnesses and connectors for wear and protect them from heat and abrasion; secure loose wiring away from hot exhaust components.
  • If you notice MIL, misfires, or poor fuel economy, address promptly to avoid catalyst contamination from prolonged rich/lean conditions.
• Software/updates:
  • Ensure the vehicle has the latest OEM software updates if recommended by Ford for emissions and sensor control strategies.

Bottom line for Ford Escape owners

• P0155 indicates a Bank 2 Sensor 1 O2 sensor heater circuit fault. Start with a thorough electrical diagnosis of the heater circuit (fuse/relay, wiring, connector) and inspect the sensor itself. Replacing the sensor is the most common solution when the heater element is confirmed defective; however, wiring or fuse issues are equally possible and should be ruled out first to avoid unnecessary sensor replacement.
• Given the data in the provided dataset, there are no P0155 complaints or recalls for this model in that specific dataset, so you should rely on standard diagnostic procedures and your local dealer or trusted shop's experience if you’re uncertain.

If you want, I can tailor a step-by-step diagnostic script for your exact Escape trim and engine (1.5L EcoBoost, 2.0L EcoBoost, or Hybrid variants) and provide a precise fuse/relay map and sensor location based on your VIN.