P0155 Code: Toyota Corolla (2020-2024) - Causes, Symptoms & Fixes

No recalls found in NHTSA database.

Data note: The provided NHTSA data for Toyota Corolla (2020-2024) includes one owner complaint tied to P0401 (emissions/EGI) and has no recalls listed. There is no P0155 entry in the supplied data. This guide uses general automotive diagnostic knowledge for P0155 in a 2020-2024 Toyota Corolla while clearly noting data limitations.

1. CODE MEANING AND SEVERITY

• Code: P0155
• Full meaning: O2 Sensor Heater Circuit Malfunction (Bank 2 Sensor 1). In plain terms, the heater element inside the Bank 2, Sensor 1 oxygen sensor (upstream sensor on the Bank 2 side) is not being heated properly or the heater circuit is not functioning as commanded.
• What it implies: The oxygen sensor may never reach its optimal operating temperature quickly enough. That slows the sensor’s response to the air-fuel mixture, which can degrade emissions control, reduce fuel economy, and possibly cause the catalytic converter to operate outside ideal conditions.
• Severity: Moderate to high for emissions and long-term efficiency. It is commonly not a direct safety concern, but prolonged heater failure can lead to degraded catalyst efficiency and failed emissions tests. In some driving conditions, the engine may run a bit lean/rich until the sensor heats up and stabilizes.

2. COMMON CAUSES ON TOYOTA COROLLA

• Faulty Bank 2 Sensor 1 O2 heater element or heater circuit (most common cause).
• Damaged or corroded wiring or connectors to Bank 2 Sensor 1 (pinched insulation, water intrusion, loose connections).
• Blown fuse or relay affecting the O2 sensor heater circuit or the ECU’s control of the heater.
• Poor or intermittent ground for the sensor circuit.
• Sensor itself degraded or contaminated, leading to heater not functioning properly or the sensor failing altogether.
• ECU/PCM command issues or wiring harness faults (less common, but possible in electrical faults).
• Aftermarket exhaust work or contaminants (oil/fuel leaks, silicone sealants, etc.) interfering with sensor readings or heater operation (more indirect).
• In some cases, a failing upstream sensor or downstream sensor (other O2 sensors) can create related diagnostic confusion, but P0155 is specifically heater circuit for Bank 2 Sensor 1.

3. SYMPTOMS

• Check Engine Light (Malfunction Indicator Lamp) illuminated.
• Bank 2 Sensor 1 heater circuit-related freeze-frame data or quick-check readiness monitors may show abnormal readings.
• Potentially slower or delayed O2 sensor response during cold starts or after engine startup until the sensor heats up.
• Possible minor impact on fuel economy and increased tailpipe emissions.
• In some cases, no noticeable drivability symptoms; the car may run normally aside from the MIL.

4. DIAGNOSTIC STEPS
   Note: Work safely around exhaust components and oxygen sensors. If you’re not comfortable with electrical diagnostics, consider professional help.

A. Verify the DTC and data

• Use a scan tool to confirm P0155 is current, verify freeze-frame data, and check for other related codes (e.g., other O2 sensor codes, misfire codes, fuel trim codes).
• Check live data for Bank 2 Sensor 1: verify the heater status (is the heater commanded ON? what is the sensor voltage when cold vs. warmed?).

B. Visual inspection

• Inspect the Bank 2 Sensor 1 O2 sensor and its wiring harness for damage, abrasion, or signs of heat exposure.
• Check the connector pins for corrosion, bent pins, or loose/poorly seated connectors.
• Inspect for oil/fuel/water contamination around the sensor area and along the wiring harness.

C. Electrical checks (heater circuit)

• Check fuses and wiring to Bank 2 Sensor 1 circuit(s) that power/communicate the heater. Look for a blown fuse, damaged relay, or a broken wire.
• With the engine off, inspect resistance of the heater circuit:
  • Disconnect the sensor connector and measure resistance across the heater terminals with a multimeter.
  • Typical healthy O2 sensor heater resistance is low (roughly several ohms; many sensors are in the single-digit to low-teens ohms range). An open circuit (very high or infinite resistance) suggests a bad sensor or broken heater wiring.
• With the engine at operating temperature and the ignition ON/engine running, command the heater ON (via scan tool if supported) and verify heater current/voltage:
  • The heater should be supplied with ~12V when commanded ON, and you should see continuity/steady voltage on the heater circuit.
  • If there is no voltage or current directed to the heater despite the ECU commanding it ON, suspect wiring, fuse, ECU control, or a faulty sensor.
• Check ground integrity: ensure the sensor’s ground path is solid and not corroded or high-impedance.

D. Sensor health and response checks

• If heater tests above pass but the code persists, remove and inspect/compare Bank 2 Sensor 1 reading versus expected behavior:
  • When the engine warms, Bank 2 Sensor 1 should transition from a slower, higher-mV activity during cold start to a stable signal around stoichiometric (around 0.45V for many sensors, but you’ll rely on your vehicle’s sensor data as baseline).
  • A sensor that never heats properly will have sluggish response to temperature changes; the ECU may flag P0155.
• Consider swapping a known-good sensor (or using a diagnostic spare) to confirm whether the sensor itself is defective.

E. Other system checks

• Inspect for vacuum leaks, misfires on Bank 2, or downstream effects that might confound sensor readings. While not direct causes of P0155, such issues can complicate diagnosis.
• If all electrical checks pass and the code remains, the ECU/PCM could be misreporting, though this is uncommon. Reflash/repair would be considered by a dealer if suspected.

F. Final confirmation

• After repairs or replacements, clear the DTC, drive the vehicle under typical conditions, and verify that the P0155 reappears or not. Confirm that no other O2 sensor faults reappear.

5. RELATED CODES

• O2 sensor family (P0130-P0155 and related):
  • P0135, P0136, P0137, P0138, P0139 — Bank 1 Sensor 1/2 heater or signal issues (examples for reference)
  • P0140, P0141 — Bank 1 Sensor 2 heater or signal issues
  • P0150, P0151, P0152, P0153, P0154, P0156 — Bank 2 Sensor 1/2 heater or signal issues
• Other emission-related codes that sometimes accompany sensor heater faults:
  • P0420 — Catalyst Efficiency Below Threshold (if catalytic efficiency is affected and a heater fault persists)
  • P0171/P0174 — System too lean/rich (fuel trim may be impacted while the sensor heater is in trouble)
• Note: The presence of related sensor codes can help triangulate whether the issue is sensor-specific, wiring, or a broader ECU problem.

6. REPAIR OPTIONS AND COSTS (2025 PRICES)
   Prices vary by region and labor rates, but here are typical ranges for a 2020-2024 Toyota Corolla. All estimates assume a Bank 2 Sensor 1 O2 sensor replacement and basic diagnostics.

• O2 sensor (Bank 2 Sensor 1) replacement
  • Parts: $40–$140 (aftermarket vs. OEM; Denso/NTK/OEM equivalents fall here)
  • Labor: 0.6–1.0 hours (shop rates commonly $90–$150/hour; local rates vary)
  • Total: roughly $120–$300
• O2 sensor + wiring/connector repair (if wiring/connector damage is found)
  • Parts: sensor plus wiring harness or repair pigtail: $20–$100
  • Labor: 0.8–1.5 hours
  • Total: roughly $160–$450
• Fuse/relay replacement (if the issue is a blown fuse or faulty relay)
  • Parts: $5–$30 for parts
  • Labor: 0.1–0.4 hours
  • Total: roughly $15–$150
• Sensor replacement plus ECU/PCM concerns (rare)
  • Parts: possible ECU replacement is substantial
  • Labor: 2–6 hours plus diagnostic
  • Total: $500–$1500+ (ECU work is uncommon for a heater circuit fault)
• If multiple O2 sensors or downstream issues are implicated
  • Parts: multiple sensors
  • Labor: proportionally higher
  • Total: $300–$900+ depending on parts and scope

Note: If the diagnostic points to a fault in the wiring harness or a damaged connector rather than the sensor itself, costs can vary widely. Always verify whether the issue is isolated to Bank 2 Sensor 1 or involves other O2 circuits before ordering parts.

7. DIY VS PROFESSIONAL

• Do-it-yourself pros:
  • Replacing an O2 sensor is a common DIY task for experienced shade-tree mechanics with basic hand tools.
  • Pros: cost savings on labor, quick swap for a known good OEM/ aftermarket sensor, direct inspection of wiring and connectors.
  • Cons: working around exhaust systems; mis-wiring or cross-threading sensors can cause additional issues; improper disconnection/installation can trigger other codes.
• DIY-considered cautions:
  • Use proper safety gear; avoid skin contact with hot exhaust components.
  • After replacing, clear codes and perform a test drive to confirm the fix.
  • Some Toyota-specific technicians use manufacturer software to verify heater command status; if you don’t have access to that, you’ll rely on standard OBD-II data and test drive results.
• Professional route:
  • Recommended for intermittent codes, suspected ECU/firing issues, or if multiple sensors show heater fault symptoms.
  • Pros: precise fault isolation, proper fuel trim diagnosis, and dealer-level tooling; able to re-flash ECU if needed.
  • Cons: higher upfront cost, longer diagnostic time if part of a broader electrical issue.

8. PREVENTION

• Use quality oxygen sensors from reputable brands or OEM-equivalents designed for Toyota. Cheap/unknown brands can cause intermittent faults.
• Adhere to service intervals for O2 sensors (as recommended by Toyota or the sensor manufacturer). Do not push sensors far beyond their expected life without inspection.
• Keep electrical connections clean and dry. Corrosion and moisture can cause heater circuit faults.
• Address engine oil leaks, coolant leaks, or fuel system issues promptly; sensor exposure to oil/fuel contaminants can degrade sensor performance.
• Avoid aftermarket modifications that may alter exhaust gas composition or sensor placement unless properly tuned.
• Maintain proper engine cooling and avoid overheating, which can degrade sensor components, including the heater element.
• Regularly inspect wiring harness routing to ensure it does not rub against hot surfaces or moving parts.

Important data caveats

• This guide is based on general P0155 diagnostic practice and common Toyota Corolla behavior, not on a P0155 case from the provided NHTSA data (the data set contains no P0155 entries and thus has limited direct statistical context for this code). The “No recalls found in NHTSA database” statement applies to the supplied data.
• Real-world results will vary by vehicle condition, maintenance history, aftermarket parts, and market region. Use this guide as a structured diagnostic framework and confirm with your specific vehicle data.