P0155
O2 Sensor Circuit No Activity Detected (Bank 2 Sensor 1)
Powertrain Emission Controls O2 Sensor Circuit 🟡 Moderate — Fix within a week
💬
What This Actually Means
In plain language — no jargon

The oxygen sensor on Bank 2 (passenger side) isn't sending any signal to the engine computer, like a smoke detector with dead batteries that never alerts. The ECU can't monitor exhaust oxygen levels, so it can't properly adjust fuel mixture.

⚡
Symptoms You May Notice
3 known symptoms for this code
Check Engine Light illuminated
Rough idle or hesitation during acceleration
Reduced fuel economy and black smoke from exhaust
🔬
Embedded Systems Insight
What the ECU/ECM is actually computing

The ECU monitors voltage fluctuations from the O2 sensor to determine if exhaust is rich or lean. The sensor should produce a switching voltage between 0.1V and 0.9V within a specific frequency range. When no voltage activity is detected within a monitoring period, the ECU sets this fault code.

Voltage & Parameter Thresholds

Parameter Normal Range Fault Condition
O2 Sensor Voltage Activity 0.1–0.9V with frequent switching No voltage change or stuck voltage for extended period
Signal Response Time Switches within 100ms cycles No switching detected or response too slow
🔧
Diagnostic & DIY Fix Guide
Check these in order — from cheapest to most complex
1
Oxygen sensor wiring and connectors
Inspect the O2 sensor connector on Bank 2 for corrosion, loose pins, or damaged wires and clean or reseat as needed.
2
O2 sensor (Bank 2, Sensor 1)
Replace the upstream oxygen sensor on the passenger side exhaust manifold with an OEM or quality replacement.
3
Engine control module (ECM) harness
Check for broken or corroded wires in the ECM harness leading to the O2 sensor circuit and repair as needed.