P0155 Code: Toyota Tacoma (2016-2023) - Causes, Symptoms & Fixes

Comprehensive diagnostic guide for OBD2 code P0155 on 2016-2023 Toyota Tacoma

Note on data sources

• Real NHTSA data for this make/model/year/issue: No owner complaints found.
• Official recalls in NHTSA database: No recalls found.
• No recalls found in NHTSA database. Data limitations: the absence of complaints/recalls in the provided data does not guarantee absence in the wild; it simply means the dataset here has nothing to report for this specific code and model. Use the guide as a diagnostic aid in addition to your vehicle’s service history and current symptoms.

CODE MEANING AND SEVERITY

• What the code means: P0155 is an OBD-II diagnostic trouble code indicating a malfunction in the O2 (oxygen) sensor heater circuit for Bank 2 Sensor 1 (the upstream oxygen sensor on the bank of the engine designated as Bank 2).
• Bank 2 Sensor 1 location: On a V6 engine like the Tacoma’s, Bank 2 is the non-primary bank; Sensor 1 is the upstream sensor before the catalytic converter on that bank. In practical terms, this is the first oxygen sensor on the exhaust stream for the second bank.
• Why it matters: The O2 sensor heater helps the sensor reach operating temperature quickly. If the heater circuit is faulty, the sensor may operate slowly or never reach the proper temperature, leading to delayed/incorrect air-fuel readings, reduced fuel economy, higher emissions, and a stored MIL (malfunction indicator light).
• Severity: Moderate. It can cause the engine to run in open-loop longer than ideal, degrade fuel economy, raise emissions, and may mask other issues. Some vehicles may still run fine without immediate driveability problems, but activating readiness monitors and ensuring proper emissions testing will be impacted.

COMMON CAUSES ON TOYOTA TACOMA

• Faulty Bank 2 Sensor 1 O2 sensor (the sensor itself is bad or its heater element has failed).
• Damaged or corroded wiring to the Bank 2 Sensor 1 heater circuit (chafed insulation, cracked connectors, moisture intrusion).
• Faulty connector or electrical connection at the sensor (loose, pushed-out, or dirty pins).
• Blown or weak fuse/relay feeding the O2 sensor heater circuit (or a wiring short to battery voltage or ground in the heater circuit).
• PCM/ECU driver issue or intermittent fault in the ground path for the heater circuit (less common but possible).
• Exhaust leaks upstream of the Bank 2 Sensor 1 that alter sensor readings and heater operation (less common as a root cause, but can affect sensor performance).
• Aftermarket sensors or improper torque/timing during replacement causing intermittent contact.
• Mechanical exhaust changes or contamination around the sensor (oil, coolant, or fuel additives) affecting heater performance (less common for heater-specific failures).

SYMPTOMS

• Check engine light (MIL) illuminated or stored codes (P0155).
• Poor fuel economy or suboptimal engine performance due to delayed sensor heating and improper fuel trims.
• Hesitation or rough idle in certain operating conditions, especially when the engine is cold.
• Possible diagnostic readiness monitors not setting (emissions-related monitors may fail to complete).
• In some cases, no obvious drivability issue if the rest of the engine management compensates sufficiently.

DIAGNOSTIC STEPS

Prepare with the right tools: a two-headed digital OBD-II scan tool that shows live sensor data, a digital multimeter, a basic automotive oscilloscope if available, and standard hand tools. Always disconnect power and follow safety protocols when testing electrical circuits.

A. Confirm and document

• Retrieve DTC P0155 with an OBD-II scanner. Write down any freeze-frame data, engine temperature, and current drive conditions when the code stored.
• Note whether the MIL is currently on or just stored. Check related codes (P0150-P0154 family for Bank 1 or other oxygen sensor faults) to look for parallel issues.

B. Visual inspection

• Inspect Bank 2 Sensor 1 harness and connector for signs of wear, corrosion, oil/fuel leaks, moisture, or damaged pins.
• Check surrounding wiring for chafing against heat shields or exhaust components.
• Inspect the upstream (pre-cat) area of Bank 2 for signs of oil or coolant leaks that could contaminate the sensor.

C. Electrical tests (wiring and sensor)

• Check fuses/relays: find the fuse for the O2 sensor heater circuit (per vehicle fuse box diagram) and verify continuity; replace any blown fuse or suspect relay.
• Resistance check of the O2 heater (sensor itself):
  • With the sensor disconnected, measure the heater element resistance across the two heater terminals using an ohmmeter.
  • Typical O2 sensor heater resistance varies by sensor type and manufacturer; many upstream heated O2 sensors read roughly in the single-digit to low-teens ohms range (e.g., approximately 5–20 ohms). If you read an open circuit (infinite resistance) or a very abnormally high value, the sensor is likely failed and should be replaced.
• Power/ground check:
  • Back-probe the sensor harness to verify presence of 12V supply to the heater pin when the ignition is on or the engine is cranking (per the service manual) and a good ground reference on the heater ground pin.
  • If there is no 12V feed or the ground path is degraded, the problem may be wiring, a fuse, or PCM/driver related.
• Sensor data comparison:
  • With the engine at operating temperature (or at least warmed up), observe Bank 2 Sensor 1 voltage and heater status in live data:
    • Upstream O2 sensor voltage (Bank 2 Sensor 1) should cycle in the roughly 0.1–0.9 V range as the engine runs, with the sensor heating up quickly when the heater is active.
    • If the heater is not active, the sensor voltage may be erratic or biased due to a slow-heating sensor or a fault in the circuit.
  • If the heater circuit is confirmed active (or expected to be) but the sensor remains cold or slow to respond, the heater itself or its control circuit may be defective, or the PCM may not be energizing it correctly.
• If you can access the sensor:
  • Compare Bank 2 Sensor 1 readings to Bank 1 Sensor 1 (P0135/P0136 equivalents) readings to see if both sensors show abnormal behavior, which could indicate a broader exhaust/PCM issue rather than a single heater failure.
• Post-replacement verification:
  • If you replace the sensor, clear the codes and drive the vehicle under normal conditions for a few cycles to allow the PCM to re-learn and the O2 sensors to reach operating temperature.

D. When to escalate

• If the heater circuit resistance is within spec, fuse/relay is good, wiring appears intact, and there is still a P0155 after several driving cycles, consider PCM-related issues or an intermittent fault in the Bank 2 Sensor 1 path. In this case, professional diagnosis with more advanced test equipment and a known-good replacement sensor may be warranted.
• If multiple O2 sensor heater codes appear (P0155 along with P0156, P0157, etc.), the root cause may be broader wiring harness contamination, PCM issues, or multiple sensor failures; a professional diagnosis is advised.

RELATED CODES

• Commonly associated O2 sensor-related codes include:
  • P0150–P0154: Other Bank 2 O2 sensor circuit faults (compressing the same sensor family: Bank 2 sensors, downstream/upstream, and heater circuits).
  • P0130–P0135: Bank 1 O2 sensor circuit faults (for comparative diagnostics on a V6 Tacoma, especially if more than one sensor is implicated).
  • P0156–P0159: Bank 2 sensor heater circuit faults on various sensor positions (heater-specific variants).
• If you see any of these alongside P0155, inspect the corresponding sensors and wiring more broadly.
• Diagnostics should also consider generic emissions-related codes (P0420, P0430) if sensor readings are disturbed, though those codes point to catalyst efficiency rather than heater circuits specifically.

REPAIR OPTIONS AND COSTS (2025 PRICES, approximate)

Prices vary by region, shop, and whether you use OEM or aftermarket sensors. The following are typical ranges to give you a ballpark.

• O2 sensor Bank 2 Sensor 1 replacement (typical upstream sensor)

  • Parts: $60–$230 (aftermarket sensors can be cheaper; OEM Toyota sensors can be at the higher end)
  • Labor: 0.5–1.0 hour (often around 0.6–1.0 hour)
  • Total: roughly $120–$350 depending on parts choice and local labor rate

• O2 sensor heater circuit repair (wiring or connector)

  • Parts: usually minimal (if only connector or a small harness repair is needed)
  • Labor: 0.5–1.0 hour
  • Total: roughly $100–$250 (depends on access and whether harness routing requires replacement)

• Sensor replacement with PCM/driver issue

  • If the issue is traced to the PCM or a driver circuit, the cost can rise significantly due to diagnostics and potential PCM repair or replacement
  • Expect higher labor charges and possible module replacement cost; in most cases this is less common than a sensor or wiring fault

• Optional related repairs

  • Fuse/relay replacement: $10–$40 for parts
  • Exhaust leaks repair near the upstream sensor: $100–$300 depending on location and labor

DIY vs PROFESSIONAL

• DIY-friendly cases:
  • Replacing Bank 2 Sensor 1 O2 sensor is within reach for a mechanically inclined DIYer with basic hand tools and anO2 sensor socket. This is typically the most cost-effective fix when the sensor is suspected to be failing.
  • Simple wiring harness inspection, connector cleaning, and gasket checks around the sensor area can be done with basic tools.
  • After replacing the sensor, clear codes and drive to allow the PCM to relearn.
• When to call a professional:
  • If you don’t have the right tools to measure heater resistance, voltage, and ground, or you suspect PCM-related issues.
  • If there is significant corrosion, wiring damage, or hard-to-reach connectors that require specialized extraction or replacement.
  • If multiple codes are present or you suspect exhaust leaks or catalytic issues that require more thorough emissions testing.
  • If replacement does not resolve the code after a reasonable drive cycle, professional diagnostics can help determine root cause more efficiently.

PREVENTION

• Use quality fuel and maintain good fuel system hygiene to minimize contamination/impacts on sensors.
• Address exhaust leaks promptly, especially upstream of oxygen sensors, to prevent erroneous readings.
• Regularly inspect wiring and connectors for wear, moisture, or corrosion, especially in areas near heat shields, exhaust, and high-vibration zones.
• When replacing sensors, use quality sensors (OEM or reputable aftermarket) and install with proper torque and anti-seize when appropriate.
• Keep your engine in good tune: addressing misfires, vacuum leaks, and ignition issues reduces stress on the exhaust sensors and helps the heater circuits function more reliably.
• Periodic diagnostic scans can catch heater-circuit faults early before they trigger multiple codes or emissions failures.

Final notes

• The provided data indicates no recalls or complaints in the dataset for this exact issue on the 2016-2023 Toyota Tacoma. The diagnostic approach above reflects typical OBD-II operational logic and Toyota-specific sensor layout. If your vehicle exhibits unusual symptoms or sensor behavior beyond the steps outlined, consult a qualified technician who can perform a deeper electrical and mechanical inspection, including a possible sensor path trace or OEM service procedure review.

If you’d like, I can tailor the diagnostic steps to your exact Tacoma configuration (2.7L 4-cylinder or 3.5L V6, trim level, exhaust setup) and help you estimate a precise parts/labor range for your local area.