P0145
O2 Sensor Circuit High Voltage (Bank 1 Sensor 3)
Powertrain Emission Controls O2 Sensor Circuit 🟡 Moderate — Fix within a week
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What This Actually Means
In plain language — no jargon

Your downstream oxygen sensor (after the catalytic converter) is sending a signal that's too high, like a broken volume knob stuck at maximum. The engine computer expects this sensor to fluctuate between certain voltage levels, but it's staying pegged high.

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Symptoms You May Notice
3 known symptoms for this code
Check Engine Light illuminated
Possible rough idle or hesitation during acceleration
Fuel economy may worsen slightly
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Embedded Systems Insight
What the ECU/ECM is actually computing

The downstream O2 sensor produces a voltage signal (0.1–0.9V) that indicates exhaust oxygen content. The ECU monitors this voltage and expects it to toggle between rich and lean states. If voltage remains consistently high (above 0.8V), the ECU detects a fault—indicating either a wiring short, failed sensor, or exhaust leak upstream.

Voltage & Parameter Thresholds

Parameter Normal Range Fault Condition
O2 Sensor Voltage (Bank 1, Sensor 3) 0.1–0.9V, oscillating Sustained >0.8V (high voltage condition)
Signal Response Time Quick transitions between states Slow or no voltage change detected
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Diagnostic & DIY Fix Guide
Check these in order — from cheapest to most complex
1
Oxygen sensor wiring harness
Inspect connector and wires for corrosion, loose pins, or damage near the sensor; reseat or clean contacts.
2
Downstream oxygen sensor (O2 sensor)
Remove and replace the sensor with a new unit, ensuring proper torque and no cross-threading.
3
Exhaust system inspection
Check for exhaust leaks upstream of the sensor that may cause false high-voltage readings.