P0155 Code: Honda Accord (2018-2023) - Causes, Symptoms & Fixes

Comprehensive diagnostic guide for P0155 on a 2018–2023 Honda Accord

Data note and limitations

• Based on the provided data: OWNER COMPLAINTS show “No NHTSA complaints found for this make/model/year/issue combination.”
• OFFICIAL RECALLS: “No recalls found in NHTSA database.”
• These data points are the only official references in this prompt. They do not rule out common, non-recalled issues or manufacturer service bulletins (TSBs) that are not listed here. For Honda-specific service bulletins beyond this dataset, consult the official Honda service information system.
• From general automotive knowledge: P0155 is an OBD-II diagnostic code related to the oxygen sensor heater circuit (typically the downstream sensor). On a Honda Accord, this often points to the downstream O2 sensor heater circuit (Bank 2 Sensor 2) or its wiring, but definitions can vary slightly by platform. Always confirm with the vehicle’s service data when possible.

CODE MEANING AND SEVERITY

• Code: P0155
• Common definition (general OBD-II): O2 Sensor Heater Circuit Malfunction (Bank 2 Sensor 2)
  • The heater element for the downstream O2 sensor is not functioning correctly, or there is an abnormal condition in the heater circuit such as a short or open.
  • In many vehicles, the downstream O2 sensor (sensor after the catalytic converter) uses a heater to reach operating temperature quickly. If the heater is faulty, the sensor may take longer to warm up, delaying accurate exhaust gas monitoring and the readiness of the catalytic converter’s emission control.
• Severity and impact on the Accord:
  • Emissions-related: can affect catalytic converter efficiency monitoring and may cause elevated emissions and a failed inspection in some regions.
  • Driveability: typically not a direct or immediate driveability issue; most drivers won’t notice a rough-running engine, but you may notice MIL (Check Engine Light) illumination and potentially reduced fuel economy if the PCM adjusts fueling during prolonged heater issues.
  • If the heater circuit is severely open or shorted, the MIL may illuminate on one drive cycle and may illuminate on consecutive cycles, depending on the OEM’s drive-cycle logic.
• Data note: No complaints data and no recalls are listed in the provided dataset for this exact scenario, so use this as a starting point and verify with live data or service information.

COMMON CAUSES ON HONDA ACCORD

• Faulty downstream oxygen sensor (Bank 2 Sensor 2) heater element
  • The most common mechanical cause: failed heater in the downstream O2 sensor.
• Wiring harness issue to the heater circuit
  • Damaged, frayed, or pin-corroded wiring or connectors near the O2 sensor.
• Connector problems
  • Loose, corroded, or water-damaged sensor connectors.
• Fuse or power/ground issue
  • A blown fuse or an intermittent ground/power supply to the sensor heater circuit.
• Electrical interference or short to ground/other circuits
  • Short to battery voltage or short to ground in the heater circuit wiring.
• Less common but possible
  • Faulty PCM/ECU control of the heater circuit (less typical, but possible if multiple heater circuits show faults).
  • Exhaust-related changes (e.g., sensor exposure to high temperature or excessive exhaust leaks) that skew readings, though the heater fault code specifically points to the heater circuit.
• Note: For Honda Accords, downstream sensors (after the cat) are common failure points with heater circuit issues as the vehicle ages or after exposure to engine heat cycles.

SYMPTOMS

• MIL/CHECK ENGINE LIGHT illuminated.
• Possible fuel economy decrease (due to imperfect O2 sensor readings affecting fuel trims if the heater never heats or heats slowly).
• In many cases, no noticeable driveability issue (car runs normally).
• Optional symptoms if the issue coincides with other sensors:
  • Slight idle fluctuations or transient exhaust smell if emissions monitoring is affected (not guaranteed).
• Emissions readiness: One or more readiness monitors may fail to set, causing emissions testing failures in states that require readiness checks.

DIAGNOSTIC STEPS

Note: Work safely around the exhaust system; O2 sensors are threaded into the exhaust and can be hot. Use proper tools and follow OEM service procedures when available.

A. Confirm and document

• Retrieve all DTCs with a scan tool; confirm P0155 as current or pending; note any other related codes (e.g., P013x, P0150-P0154, P0135-P0140).
• Record freeze-frame data and fuel trims for Bank 2 downstream sensor, if available.

B. Visual inspection

• Inspect the Bank 2 Sensor 2 (downstream O2 sensor) and its wiring:
  • Look for damaged insulation, chafing against the exhaust, or heat-related damage.
  • Check for loose or corroded connectors; verify that the sensor is firmly seated in the exhaust pipe or housing.
  • Inspect for any exhaust leaks before the sensor that could affect readings.

C. Electrical checks (power, ground, and heater circuit)

• Identify the heated O2 sensor circuit in the service manual to locate:
  • Power/12V supply to the heater circuit
  • Ground return for the heater circuit
  • Sensor heater resistance specification
• With the ignition ON (engine OFF or ON as specified by the manual):
  • Check for 12V supply at the heater circuit pin(s) of the sensor connector when required.
  • Check for a solid ground path on the heater circuit using a DVOM (digital multimeter).
• Measure the heater circuit resistance at the sensor terminals (with the sensor disconnected, if required by the procedure):
  • Compare measured resistance to the manufacturer’s specified range (you’ll typically see a resistance in a low-Ohm range; many sensors fall in the 5–20 ohms range, but refer to the service data for exact value).
  • A resistance that is infinite (open) or very low/shorted indicates a bad sensor or wiring issue.
• If you have the ability, perform a live data check:
  • With engine at operating temperature, monitor O2 sensor 2 heater status or heater current/voltage if your scanner supports it. A steady “HEATER ON” status indicates the PCM is commanding the heater; if it never switches to HEATER ON, suspect wiring, fuse, or sensor.

D. Functional swap/verification (if feasible)

• Swap test: If you have a known-good downstream Bank 2 Sensor 2 of the same type, swap temporarily (or swap the suspected sensor with an identical one) to see if the code follows the sensor.
• If the code clears after replacement and the problem does not return, the original sensor is likely at fault.

E. Related system checks

• Check for exhaust leaks upstream or around the catalytic converter, as leaks can cause incorrect downstream readings.
• Ensure engine mechanical and fuel system integrity is sound, as a misfire or other sensor readings can complicate diagnostics.

F. Post-repair verification

• Clear the codes after repair, drive normally through a few cycles, and re-scan to verify that P0155 does not return and that the downstream O2 sensor heater is functioning in live data.

RELATED CODES

• P0155 is commonly discussed alongside:
  • P0150: O2 Sensor Circuit Malfunction (Bank 2 Sensor 1)
  • P0151: O2 Sensor Heater Circuit Malfunction (Bank 2 Sensor 1)
  • P0152: O2 Sensor Heater Circuit Malfunction (Bank 2 Sensor 1) – high resistance
  • P0153: O2 Sensor Heater Circuit Malfunction (Bank 2 Sensor 1) – open/short
  • P0135–P0140: Various upstream (Bank 1/Bank 2) O2 sensor heater or circuit faults
• Other related O2-related codes that may appear with diagnostic confusion:
  • P0130–P0134: Bank 1 Sensor 1 related
  • P0141–P0144: Bank 1 Sensor 2 heater or circuit related
• Practical takeaway: If you see P0155 with other O2-related codes, address sensor wiring/connectors first, then sensor replacement, then ECU/fuse issues if needed.

REPAIR OPTIONS AND COSTS (2025 PRICES)

Note: Prices vary by region, shop, OEM vs aftermarket parts, and labor rates. The ranges below are typical ballparks for a 2018–2023 Honda Accord.

A. Downstream O2 sensor replacement (Bank 2 Sensor 2)

• Parts: $60–$180 (aftermarket to OEM; some sensors can be higher)
• Labor: 0.5–1.0 hour (typical)
• Estimated total: $100–$300
• Remarks: This is the most common fix if the heater circuit fault is due to a failed sensor. Use a sensor compatible with Honda Accord (pre-cat vs post-cat sensor type varies by engine; ensure you buy the correct downstream sensor for Bank 2).

B. Wiring harness/connector repair or replacement

• Parts: $10–$100 (connector or pin repair; wiring harness segments if damaged)
• Labor: 0.5–2.0 hours (diagnostic time plus repair)
• Estimated total: $100–$500
• Remarks: If the fault is a damaged harness, connector corrosion, or a wiring short, labor costs can be higher due to thorough inspection and reseating. This can be necessary if the sensor itself tests fine but the circuit shows faults.

C. Fuses and power/ground fixes

• Parts: typically minimal
• Labor: 0.25–0.5 hours
• Estimated total: $50–$150
• Remarks: If a fuse or poor grounding caused the issue, this is a cost-effective fix.

D. PCM/ECU related fault

• Parts: $0–$900 (rare)
• Labor: variable
• Estimated total: $0–$900
• Remarks: Only consider if multiple O2 sensor circuits fail or there are multiple controller-related fault codes that indicate a controller issue. This is uncommon for a single P0155 code.

E. OEM vs aftermarket parts

• Aftermarket sensors generally cost less; OEM sensors may cost modestly more but can match factory spec and sensor warm-up characteristics. For emissions-critical components, OEM is often favored by some shops for reliability over long-term ownership.

DIY vs PROFESSIONAL

• DIY feasibility: Medium
  • If you have basic automotive electrical skills, a DMM/scan tool, a few common hand tools, and a torque wrench, you can:
    • Inspect and reseat connectors
    • Check for obvious wiring damage
    • Replace a downstream O2 sensor (Bank 2 Sensor 2) using the correct sensor type
    • Clear codes and test-drive to verify
  • Tools and safety: O2 sensor socket, anti-seize compound for threads (do not apply anti-seize to the sensor tips; apply to threads only if the factory manual permits), proper PPE.
  • Risks: O2 sensors are hot; improper installation can cause exhaust leaks, improper seating can lead to sensor misreadings, and cross-threading can ruin the exhaust pipe.
• Professional route: Recommended if you are not comfortable with electrical diagnostics, or if the fault persists after a straightforward sensor replacement.
  • Pros: Accurate diagnosis, proper wiring checks, assurance of emissions compliance, warranty on parts and labor.
  • Cons: Higher upfront cost than DIY in many markets.

DIY tips

• Use a quality OBD-II scanner that can display live data and heater status for O2 sensors (HEATER status or oxygen sensor data).
• If you replace the sensor yourself, ensure you drive the car for several drive cycles to confirm the MIL stays off; some vehicles need two consecutive drive cycles to clear pending or mile-based monitors.
• Ahold of the exact torque specification for the downstream sensor from Honda service data to ensure proper tightening (over-tightening can damage the sensor threads; under-tightening can cause leaks).

PREVENTION

• Regularly replace O2 sensors at intervals recommended by Honda for your engine (downstream sensors typically have a longer interval than upstream ones, but aging sensors can still fail).
• Keep the exhaust system intact: fix exhaust leaks promptly, as leaks can affect downstream sensor readings.
• Use quality fuel and maintain an efficient catalytic converter; improper combustion or converter damage can influence the sensor readings.
• Inspect sensor connectors during routine maintenance (air filter changes, spark plug service) to catch corrosion or loose connections early.
• Avoid harsh engine treatments or fuel additives that could contaminate sensors or degrade heater elements; use approved products and follow manufacturer guidelines.

Final notes

• Based on the provided data, there are no recalls listed for this issue on the 2018–2023 Honda Accord, and there are no NHTSA owner complaints in the dataset for P0155. No recalls found in NHTSA database.
• If you’re pursuing this at a shop, provide the above diagnostic steps and be prepared to show live data restoring the heater function after any sensor swap.
• If the code reappears after a sensor replacement, recheck the wiring harness and connectors, then consider alternate causes such as ECU-related faults or catalytic converter concerns as indicated by other related codes and vehicle symptoms.

If you’d like, I can tailor a step-by-step DIY procedure with the exact torque specs, connector pinouts, and a recommended diagnostic sequence for your specific engine variant (e.g., 1.5L turbo vs. 2.0L turbo) within the 2018–2023 Accord lineup.