P0155 — O2 Sensor Heater Circuit (Bank 2, Sensor 1) #

Note: The code description may vary depending on the vehicle manufacturer.

• O2 Sensor Heater Circuit Malfunction (Bank 2 Sensor 1) — Toyota, Lexus
• Oxygen Sensor Heater Circuit Malfunction (Bank 2, Sensor 1) — Ford, GM, Chrysler
• Heated Oxygen Sensor Heater Circuit (Bank 2 Sensor 1) — Honda, Nissan

Summary of Code P0155 #

P0155 is a diagnostic trouble code (DTC) indicating a fault in the heater circuit of the upstream oxygen sensor (O2 sensor) located on Bank 2 (the side of the engine without cylinder #1). The heater inside the O2 sensor helps it reach optimal operating temperature quickly, especially during cold starts. When the Engine Control Module (ECM) or Powertrain Control Module (PCM) detects that the heater circuit isn’t working properly, it sets this code. This malfunction can affect engine performance, fuel economy, and emissions, particularly in cold conditions. Since O2 sensors are critical for the ECM to adjust the air-fuel mix, a heater issue can disrupt precise engine control.

Frequent Symptoms for Code P0155 #

A faulty O2 sensor heater circuit doesn’t always cause obvious driveability problems, but certain symptoms may appear, especially on cold starts or during initial engine warm-up. Watch for these signs:

• Illuminated Check Engine Light (CEL)
• Poor fuel economy — slight drop due to delayed sensor feedback
• Rough idle (mainly when cold)
• Failed emissions test (increase in exhaust pollutants)
• Sluggish engine response until the engine warms up

Likely Causes for Code P0155 #

The majority of P0155 cases are traced back to problems with the O2 sensor itself, but other issues in the heater circuit can be at fault. Here are the most common causes, ranked by frequency:

1. Faulty O2 sensor heater element (internal failure)
2. Blown fuse in the sensor heater circuit
3. Wiring issues — open circuit, short to ground or short to power
4. Poor electrical connections or corroded terminals at the sensor or harness
5. Faulty relay (if used in sensor heater circuit)
6. ECM/PCM fault (rare)

Step-by-Step Diagnosis for Code P0155 #

Diagnosing P0155 requires a logical approach to pinpoint the cause. OEM repair information should always be referenced for wiring diagrams and specifications. Here’s a structured process:

1. Check for other codes: Address additional O2 sensor or heater codes first, as they may be related.
2. Visual inspection: Examine the O2 sensor harness for visible damage, burned wires, or loose/corroded connectors.
3. Test the heater circuit fuse: Replace if blown and check for root cause of overcurrent.
4. Check power and ground at O2 sensor: Use a multimeter with the ignition on; compare readings to OEM specs.
5. Measure sensor resistance: Disconnect the sensor and measure heater element resistance (typically 5–20 ohms; refer to OEM specs).
6. Test for continuity and shorts: Inspect wiring between the sensor and the ECM/PCM for breaks or shorts.
7. Substitute with a known-good sensor (if available): Helps isolate sensor vs. wiring/ECM issue.
8. Test ECM/PCM output (last resort): If all else checks out, the ECM/PCM may be at fault (rare).

Possible Repairs for Code P0155 #

The fix for P0155 depends on the exact fault found during diagnosis. Here are the most common repairs:

• Replace the O2 sensor (Bank 2, Sensor 1) if the heater is open or out of spec
• Repair or replace damaged wiring or connectors
• Replace blown fuse and correct underlying wiring faults
• Replace faulty relay (if applicable to the circuit)
• Repair or replace the ECM/PCM (extremely rare; confirm all other possibilities first)

Is It Safe to Drive with Code P0155? #

Limited: While P0155 typically won’t cause immediate drivability problems or leave you stranded, driving long-term with this code is not advised. The engine may run less efficiently, emissions will increase, and you may fail a state inspection. If you notice rough running or poor fuel economy, get it fixed soon to avoid further issues.

Vehicles Most Commonly Affected by P0155 #

P0155 can appear on nearly any OBD-II compliant gasoline vehicle, but is most often seen in:

• Toyota and Lexus V6 and V8 engines
• Ford F-series trucks and SUVs (modular V8)
• Chevrolet and GMC trucks (V8, V6)
• Chrysler and Dodge (3.6L V6, Hemi V8)
• Honda and Nissan V6 engines

This list is not exhaustive; the code can occur on any multi-bank engine with heated O2 sensors.

Common Mistakes & Best Practices for P0155 #

Rushing to replace the sensor without proper diagnosis is a frequent error. Best practices can save time and money:

• Don’t replace the O2 sensor before checking fuses and wiring
• Always inspect connectors for corrosion or loose pins
• Use OEM or high-quality sensors; cheap aftermarket sensors can fail prematurely
• Clear the code after repairs and perform a road test to confirm the fix
• Refer to the OEM wiring diagram for your vehicle before probing circuits

Express FAQ — P0155 #

Having trouble understanding the code or next steps? Here are quick answers:

• Q: Can a bad O2 sensor heater affect performance?
  A: Yes, mainly during engine warm-up, as the ECM can’t adjust fueling as precisely, sometimes causing rough idle or hesitation.
• Q: Is it OK to use a universal O2 sensor?
  A: Sometimes, but OEM or direct-fit sensors are recommended for best reliability and compatibility.